Taxonomic innovations in South American Selaginella (Selaginellaceae, Lycopodiophyta): description of five new species and an additional range extension

Abstract Five Selaginella species (i.e, S. gioiae, S. papillosa, S. pubimarginata, S. rostrata, and S. xanthoneura) from Neotropical rainforests of South America are described and illustrated as new, while S. surucucusensis, originally recorded only from Brazil, is redefined to account for species’ morphological characters throughout its expanded distribution range and also a novel illustration is provided for it. Inferred taxonomic affinities and conservation assessment are offered for species here treated. Selaginella gioiae is native to Colombia, Ecuador, and Peru, and S. xanthoneura is so far only known in Colombia, whereas S. surucucusensis is now known to occur in Colombia and Venezuela in the north-central part of South America. These three species are included in the “Selaginella flabellata group” based on their habit, stem shape, rhizophores position, and mega- and microspores color, and ornamentation. Selaginella papillosa, S. pubimarginata, and S. rostrata are native to Venezuela. Selaginella papillosa and S. pubimarginata morphologically belong in the “Selaginella deltoides group” based on their habit, stem type, shape of lateral leaves and their indument type distributed on upper surface of the leaf lamina. On the other hand, S. rostrata is considered to be a member of the “Selaginella microdonta group,” which is centered in the Guiana Highlands, based on its habit, stem type, and leaf size and shape, and for which a key to identify species is provided. Finally, all species threated here are classified in subg. Stachygynandrum based on their heteromorphic leaves, mostly quadrangular strobili, and monomorphic sporophylls shape (except for S. rostrata that has slightly dorsiventral and flattened strobili with somewhat heteromorphic sporophylls).


Introduction
Selaginella, a highly diverse and species rich lycophyte genus (600-800 spp), is found in a wide variety of ecosystems almost worldwide (Valdespino 2015;Zhou and Zhang 2015;PPG I 2016;Valdespino 2016;Valdespino 2017a). Selaginella species can be classified using several subgeneric classification systems as discussed in Valdespino and López (2019). In the New World, there are some 350 described Selaginella species, most of them in Neotropical ecosystems, and the number of species described from this region has steadily increased during the last decades. The latter is the result of contemporary field studies that have yielded additional collections, critical revision of herbarium material incorporating detailed microscopic analyses, and overall reassessment of previously known taxa. This tendency will most likely continue, particularly as local and regional taxonomic monographic studies and phylogenetic analysis using molecular data of infrageneric groups are undertaken. The aim of the present contribution is to further document Selaginella diversity in South America by describing five new species and revising the description and distribution range of another species described not long ago from this region.

Material and methods
I studied gross morphological features of leaves and spores of Selaginella species using herbarium specimens from AAU, B, BM, COL, CR, F, GH, HUA, INPA, K, MG, MO, NY, PMA, R, RB, S, U, UC, US, and VEN (acronyms according to Thiers 2020) using stereomicroscopes (i.e., Olympus SZ 60-STS at the New York Botanical Garden and Olympus SZX16 at the University of Panama herbaria). I further studied fine surface details of leaves and spores using a Zeiss Model Evo 40vp Scanning Electron Microscope (SEM) at 10-15 kV at the Smithsonian Tropical Research Institute (STRI). Digitized SEM images of plant sections, leaf, and spores were taken at different magnifications, post-processed, and assembled in multipart figures using Adobe Photoshop as explained in Valdespino (2016). Terminology, measurements, and conservation status used in species descriptions follow Valdespino and López (2019) and references therein, while species classification is according to Weststrand and Korall (2016).

Results
I describe the five new Selaginella species S. gioiae Valdespino, S. papillosa Valdespino, S. pubimarginata Valdespino, S. rostrata Valdespino, and S. xanthoneura Valdespino, and provide an updated description and an extended distribution range for S. surucucusensis L.A. Goés & E.L.M. Assis. All these taxa are native to Neotropical rainforest ecosystems of South America where Selaginella is notably diverse and species rich. Selaginella gioiae is known to occur in Colombia, Ecuador, and Peru, whereas S. papillosa, S. pubimarginata, and S. rostrata are native to Venezuela, and S. xanthoneura is so far only known to occur in Colombia. In addition, S. surucucusensis, originally described based on scanty material from Brazil, is now shown to be a more widely distributed species with an extended geographical rage in the north-central part of South America, with specimens documenting its occurrence in Colombia and Venezuela.
All species here examined have heteromorphic vegetative leaves (at least on frondlike, aerial parts of erect species), non-articulate stems, and mostly quadrangular strobili comprised by monomorphic sporophylls (except for S. rostrata where strobili are slightly flattened and dorsiventral, composed by somewhat dimorphic sporophylls). Therefore, I consider them to belong in the broadly defined subgenus Stachygynandrum (P. Beauv. ex Mirb.) Baker.
Selaginella gioiae, S. surucucusensis, and S. xanthoneura are morphologically related to the Neotropical "Selaginella flabellata (L.) Spring group" as defined by Hieronymus (1901: 682) and Valdespino (2017a). This group comprises some thirty-five species characterized by their fern-like habit, erect stems with leaves seemingly monomorphic before branches, as well as axillary, ventral, dorsal, and occasionally, seemingly lateral rhizophores. This group is additionally defined by white to off-white megaspores with distal faces usually reticulate or rugulate-reticulate, with each reticulum open or closed, and with echinate and perforate microstructures. It also possesses orange to pale or-ange microspores with distal faces capitate to baculate, and with echinate to perforate microstructures (Valdespino 2017a). The dorsal position of rhizophores and overall echinate microspore microstructure are not unique characters to this group (Valdespino 2017a). Nonetheless, what is revealing about the "Selaginella flabellata group" is the occurrence of the three types of rhizophores on a single stem and the degree and density in which the echinate microstructure occur in capitate to baculate projections of distal faces and in the overall surface of microspores.
Selaginella papillosa and S. pubimarginata, in turn, are morphologically similar to taxa in the "Selaginella deltoides A. Braun group" (Valdespino 2016) also from South America. Most species in this group (i.e., S. aculeatifolia Valdespino, S. albolineata A.R. Sm., S. brevifolia Baker, S. deltoides, S. papillosa, S. pubimarginata, and S. sandwithii Alston) typically have a moss-like habit, creeping stems, lateral leaves broadly ovate to ovate-deltate with upper surfaces hispidulous, each hair short and resembling prickles, tooth-like or papilla-like projections, which are mostly found submarginally, marginally, and apically (except in S. albolineata and S. papillosa) along the basiscopic halves of the laminae, and conspicuous (less so on S. albolineata, S. papillosa, and S. pubimarginata), straw-colored midribs. Remarkably, in the case of S. albolineata, the lateral leaf upper surfaces are completely covered by elongate idioblasts, while idioblasts may also be present on lower leaf surfaces of other species in this group, as well as conspicuously hyaline median leaf margins.
Lastly, S. rostrata is morphologically akin to species in the "Selaginella microdonta A.C. Smith group", which is an alliance formed by species mainly found in the tepuis of the Guiana Highlands, particularly of Venezuela. This species group includes S. breweriana A.R. Sm., S. cardiophylla Valdespino, S. hemicardia Valdespino, S. microdonta (also found in Brazil), S. neblinae A.R. Sm., and S. valdepilosa Baker (also from Guyana). This group is characterized by its ribbon-like or leafy liverwort-to moss-like habit, creeping stems, small leaves, and usually broadly ovate-elliptic to broadly elliptic lateral leaves. Based on overall plant appearance, species of this group are commonly mistaken for bryophytes. Nonetheless, this is quickly dispelled as one observes their root-bearing rhizophores, found at branch forks throughout stems, heteromorphic leaves, which include two rows each of large, lateral and small, median leaves, as well as axillary leaves along stems. Furthermore, a key to identify species in the "Selaginella microdonta group" is provided.

Taxonomic treatment
Selaginella gioiae Valdespino, sp. nov. urn:lsid:ipni.org:names:77211382-1 Figures 1-5 Diagnosis. Selaginella gioiae differs from S. surucucusensis by the leaves on main stems before becoming fully heteromorphic, triangular-lanceolate, triangular-ovate or deltate (vs. ovate or broadly ovate), the leaves shortly before or after fourth to sixth or even further up along (vs. above first or second) stem branches fully heteromorphic and at this point onward lateral leaves oblong or oblong-ovate (vs. ovate or ovate-oblong), median leaf inner margins straight (vs. convex), and linear-lanceolate to lanceolate (vs. ovate to ovate-lanceolate) axillary leaves.
Type Description. Plants terrestrial. Stems erect, stramineous, 0.6-1.2 m tall, (2.0)2.5-6.0 mm diam. on main stem before first branches, non-articulate, not flagelliform, stoloniferous, 2 or 3-branched, the terminal portion of the stem similar in shape to lateral branches (i.e., conform). Rhizophores axillary, ventral, dorsal, and seemingly lateral, borne on lower-most part of the stems and throughout stolons, stout, 0.3-2.0 mm diam. Leaves seemingly monomorphic and strongly appressed to the stem shortly before or after fourth to sixth or even further up along stem branches (depending on stem length), then heteromorphic (of three kinds of leaves: median, lateral, and axillar), coriaceous, upper surface dull to shiny green, striate or striate-corrugate, lower surface shiny yellowish green to silvery green, striate, those on main stem before fully heteromorphic triangular-lanceolate, triangular-ovate or deltate, the bases prominently raised and truncate with both edges rounded or slightly subcordate and glabrous, the margins narrowly hyaline and denticulate, the apices attenuate. Lateral leaves on main stems after leaves become fully heteromorphic, distant, ascending to spreading, oblong or oblong-ovate, 2.0-4.2(5.0) × 0.9-2.2(2.5) mm; bases truncate at central portion, glabrous, acroscopic bases strongly overlapping stems, rounded, entire, basiscopic bases free from stems, geniculate; margins on upper surfaces bordered by greenish, rectangular, and laevigate cells, acroscopic margins on lower surfaces narrowly bordered continuously by a hyaline band comprised of idioblasts, the band 1-3 cells wide, the idioblasts elongate, straightwalled, and papillate, the papillae in a single row over each cell lumen, basiscopic margins on lower surfaces bordered continuously by greenish, elongate, straight-walled, laevigate cells, acroscopic margins entire to sparingly denticulate along proximal ⅔, otherwise denticulate distally, basiscopic margins entire or scarcely denticulate; apices obtuse, entire or obscurely denticulate; upper surfaces consisting of irregularly shaped, somewhat rectangular, straight to sinuate-walled cells (often difficult to distinguish because of waxy deposits), with some of these sparse-and obscurely papillate, papillae in one row on each cell lumen, without stomata or with few, obscure submarginal stomata, sparsely distributed along basiscopic margins, lower surfaces consisting of elongate, sinuate-walled cells and of elongate, straight-walled, papillate idioblasts, papillae 6-22 in one rows on each cell lumen, with stomata on 3-7 rows along central most portion of midribs. Median leaves on main stem after leaves fully heteromorphic, distant to slightly imbricate, ascending, ovate to ovate-lanceolate, 1.4-3.4 × 0.8-1.7 mm; bases glabrous, truncate to truncate-oblique, without auricles or the outer bases with a rounded nob; margins bordered continuously by a narrow hyaline band comprised of idioblasts, the band 1-3 cells wide, the idioblasts similar to those in acroscopic, hyaline marginal bands of lateral leaves, lower surfaces, the inner margins, straight, entire throughout or entire along proximal ½ and sparsely denticulate on distal ½, the outer margins convex, denticulate throughout; apices acute or attenuate, each 0.1-0.5 mm long, entire at tip or tipped by 1-3 small teeth; upper surfaces similar to those on upper surfaces of lateral leaves but more abundantly covered by irregularly arranged, papillate idioblasts, the papillae 3-14 in one row on each cell lumen, with stomata in 3-7 rows along midribs and Figure 2. Selaginella gioiae Valdespino. A Lateral leaf from stem branch, upper surface B proximal half of lateral leaf, upper surface (same leaf shown in A) C distal half of lateral leaf, upper surface (same leaf shown in A) D lateral leaf, lower surface E proximal half of lateral leaf, lower surface (same leaf shown in D) F distal half of lateral leaf, lower surface (same leaf shown in D); note, elongate and papillate idioblasts (a) and stomata along midrib (b) G median leaf from stem branch, upper surface H proximal half of lateral leaf, upper surface (same leaf shown in G) I distal half of median leaf, upper surface (same leaf shown in G); note, elongate and papillate idioblasts (a) and stomata along midrib (b) J median leaf from stem branch, lower surface K proximal half of median leaf, lower surface (same leaf shown in J) L distal half of median leaf, lower surface (same leaf shown in J). A-L taken from the holotype. few submarginal, along basiscopic ⅓ of outer margins, lower surfaces comprising elongate (somewhat jigsaw puzzle-like), sinuate-walled cells, without idioblasts and stomata. Axillary leaves on main stem after leaves fully heteromorphic linear-lanceolate to lanceolate, 2.5-4.5 × 1.0-1.7 mm; bases truncate, prominently raised, glabrous; margins as in lateral leaves, denticulate throughout; apices gradually tapering, broadly acute, tipped by 1-3 teeth; both surfaces as in lateral leaves. Strobili terminal on main stem and each branch tips, quadrangular, 0.5-5 cm long. Sporophylls monomorphic, without a laminar flap, each with a well-developed and glabrous keel along midribs, ovate-lanceolate, 1.5-2.0 × 0.6-1.0 mm; bases rounded to truncate; margins narrowly hyaline, 1 or 2 cells wide with the cells elongate, slightly sinuate-walled and glabrous, parallel to margins, denticulate throughout; apices attenuate to acuminate, the acumen 0.1-0.3 mm, tipped by 1-3 small teeth; dorsal sporophylls with upper and lower surfaces as in vegetative leaves; ventral sporophylls with both surfaces, silvery green to hyaline, comprised of elongate, papillate, sinuate-walled cells and of papillate idioblasts. Megasporangia intermixed with microsporangia along two ventral rows; megaspores white to beige colored, 325-350 µm diam., proximal faces rugulate with a strongly developed equatorial flange, the microstructure echinate to slightly granular, distal faces reticulate, the reticulae open (incomplete) to closed and the microstructure echinate and perforate. Microsporangia in two dorsal rows and intermixed with megasporangia along two ventral rows; microspores light orange, 18-20 µm diam., proximal faces rugulate-echinate on proximal faces with slightly punctate or rugulate microstructure, distal faces capitate or baculate, with each caput or bacula and the microstructure echinate or rugulate. Habitat and distribution. Selaginella gioiae grows on lowland and montane rainforests at 80-1480 m. It is known from tropical rainforest ecosystems on both sides of northwestern Andes and in the Amazon basin, specifically in western Colombia and central-eastern Ecuador and northwestern Peru. It has been collected in fertile condition from February to December.
Eponomy. This unique, tall Selaginella species is named after Christopher Gioia (1968-), who as my longtime companion has steadfastly encouraged my work on the genus.
Conservation status. Selaginella gioiae is a widely distributed species that grows at low and high elevations with collections continuously made from the late nineteenthto early in the twenty-first century over a relatively wide range in South America, which suggest it is comprised of healthy populations. Accordingly, it is here considered of Least Concern (LC) based on IUCN (2012).
Additional specimens examined (paratypes Discussion. Selaginella gioiae is characterized by its fern-like habit, erect stems, each 0.6-1.2 m tall, leaves on main stem normally fully heteromorphic shortly before or after fourth to sixth or even further shortly before or after fourth to sixth or at higher up branches depending on main stem length, with margins bordered by a narrow band of hyaline, papillate, idioblasts. On main stems it has oblong or oblong-ovate lateral leaves, median leaf bases glabrous, truncate to truncateoblique, without auricles or the outer bases rounded or with a rounded nob, linear-lanceolate or narrowly lanceolate axillary leaves, megaspores with a prominent equatorial flange, and microspores distal faces capitate or baculate, each caput or baculum usually micro-echinate. Selaginella gioiae is further notable by its median leaf lower surfaces with frequently very well defined or marked midribs and strobili tips occasionally displaying vegetative growth. Selaginella gioiae is one of the tallest species within the "Selaginella flabellata group" and among these taxa it may be confused with S. surucucusensis because of their fairly similar median leaves with inconspicuous, short-elongate or punctate idioblasts on the upper surfaces. Selaginella gioiae, however, is set aside from S. surucucusensis by the characters listed in the diagnosis and by its median leaf with the outer bases rounded or with a rounded nob (vs. with a distinct auricle) and acute, attenuate or short-acuminate (vs. attenuate or acuminate to short-aristate) apices, each less than ¼ (vs. ¼) the length of the lamina. Selaginella cuneata Mickel & Beitel is another member of the "Selaginella flabellata group" with inconspicuous short-elongate or punctate idioblasts on the upper surface of median leaves. Selaginella gioiae differs from the latter by its median leaf outer half of the lamina at least ¼ to ½ wider (vs. twice as narrow) as the inner half, and hyaline (vs. greenish) bordered margins of median leaves and on acroscopic margins of lateral leaves. Diagnosis. Selaginella papillosa differs from S. brevifolia by its median leaf inner and outer halves equal in width (vs. outer halves typically wider than the inner halves), lateral leaf upper surfaces with midribs not marked and of the same color as the rest of Description. Plants epipetric, moss-like. Stems creeping, stramineous, 5.0-15.0 cm long, 0.3-0.5 mm diam., non-articulate, not flagelliform, not stoloniferous, strawcolored, 1 or 2-branched, the branches arising at almost 90° angle. Rhizophores axillary, axillary-ventral or dorsal, borne throughout the stems, filiform, 0.1-0.2 mm diam. Leaves heteromorphic throughout, membranaceous, upper surfaces light green, lower surfaces silvery green. Lateral leaves distant, spreading to slightly ascending or slightly imbricate (at branch tips), ovate, 1.0-2.0 × 0.8-1.6 mm; bases rounded, glabrous, acroscopic bases overlapping stems, basiscopic bases free from stems; margins on upper surfaces greenish and composed of quadrangular to rounded cells, on lower surfaces bordered continuously by a hyaline band comprised of idioblasts, the band 1-3 cells wide, the idioblasts elongate, straight-walled, and papillate, the papillae in a single row over each cell lumen, acroscopic margins long-ciliate along proximal ½-⅔, otherwise dentate distally, basiscopic margins dentate along proximal ⅔, otherwise denticulate distally; apices acute, attenuate to apiculate, apiculae often falling off, tipped by 1 or 2 teeth; upper surfaces mostly glabrous, except for few, distal, teeth-like hairs near apices, comprising rounded to quadrangular, sinuate-walled, papillate cells, each cell lumen with 7-14 papillae, with few (ca. 4) submarginal to marginal stomata near central portion of basiscopic margins, lower surfaces glabrous, comprising elongate, sinuate-walled, laevigate cells and of straight-walled, papillate idioblasts, the papillae 9-15 in one row on each cell lumen, with stomata on 1-3 rows along midribs. Median leaves distant to slightly imbricate near branch tips, ascending, ovate to broadly ovate to ovate-orbiculate or elliptic with both inner and outer halves equal in width, 0.8-1.2 × 0.5-1.0 mm; bases glabrous, oblique and decurrent, without auricles; inner margins bordered continuously by a narrow hyaline band comprised of idioblasts, the band 1 or 2 cells wide, the idioblasts similar to those in the hyaline marginal bands of the lateral leaves on lower surfaces, except for papillae sometimes interconnecting, longciliate along proximal ¾, otherwise short-ciliate to dentate distally, the outer margins bordered by greenish, quadrangular to elongate, glabrous cells along proximal ½ and along distal ½ by a hyaline band comprised of idioblasts, the band 1-5 cells wide, the idioblast similar to those in the inner margins, dentate throughout; apices aristate, each arista 0.2-0.4 mm long, tipped by 1 or 2 teeth; upper surfaces glabrous, comprising rounded, sinuate-walled, papillate cells, each cell lumen with 4-15 papillae, concentrically arranged, without idioblasts, with stomata in 1 or 2 rows along midribs on distal ½ of the leaf lamina and few (1 or 2) marginal to submarginal along proximal ½ of outer margins, lower surfaces comprising elongate, sinuate-walled, glabrous cells and submedial to submarginal, sinuate-walled, papillate, idioblasts cells, the papillae similar to those in lower surfaces of lateral leaves, without stomata. Axillary leaves ovate to ovate-lanceolate, 1.2-1.5 × 0.6-1.0 mm; bases attenuate and covered by idioblasts similar to those in lower surfaces of lateral leaves, except for papillae in 1 or 2 rows on cell lumen; margins on upper and lower surfaces as in lateral leaves, ciliate along proximal ½-¾; apices acute, attenuate to apiculate, apiculae often falling off; both surfaces as in lateral leaves. Strobili terminal on branch tips, quadrangular, 0.4-5 mm long. Sporophylls monomorphic, without a laminar flap, each with a slightly developed keel along midribs, the keel glabrous or with few, short, tooth-like projections distally, ovate-lanceolate, 0.6-1.0 × 0.3-0.5 mm; bases rounded; margins narrowly bordered by a hyaline band, the band 1 or 2 cells wide with the cells elongate, slightly sinuate-walled and glabrous, shortly ciliate along proximal ½, denticulate on distal ½ or denticulate throughout; apices attenuate to acuminate, the acumen 0.1-0.3 mm long, tipped by 1 or 2 teeth; dorsal sporophylls with upper surfaces green and cells as in median leaves, except for the half that overlaps the ventral sporophylls where the surfaces are greenish hyaline to hyaline with elongate and slightly sinuate-walled cells, lower surfaces hyaline and comprising elongate, sinuate-walled cells; ventral sporophylls with both surfaces, hyaline, comprised of elongate, papillate, sinuate-walled cells. Megasporangia few and proximal, along two ventral rows; megaspores yellow, pale yellow to whitish, 270-310 µm diam., proximal faces rugulate-reticulate with a well-developed equatorial flange, the microstructure echinate and perforate, distal faces reticulate, the reticulae open (incomplete) to closed, the microstructure echinate and perforate. Microsporangia in two dorsal rows and distally along two ventral rows; microspores light orange, not measured or observed in detail.

Selaginella papillosa
Habitat and distribution. Selaginella papillosa grows at 250-1670 m in tropical rainforests at the base of Cerro Aracamuni and near the summit of Cerro Aratitiyope in the state of Amazonas, Venezuela.
Etymology. The specific epithet derives from the Latin "papilla," meaning "nipple", and refers to the abundant and distinctive papillae found on cells lumen in upper, leaf surfaces.
Conservation status. Selaginella papillosa is only known from two collections made at the base of Cerro Aracamuni, a Guiana Highland sandstone tepui, part of the Serranía de La Neblina National Park, and near the top of Cerro Aratitiyope, a granitic mountain designated as a Natural Monument, both in the state of Amazonas, Venezuela. Accordingly, the natural populations of this new species may not be threatened. However, as available data is scanty, it does not allow for a reliable conservation assessment. Therefore, the species is considered Data Deficient (DD) based on IUCN (2012).
Discussion. Selaginella papillosa is distinctive by its moss-like habit, lateral leaf with long-ciliate acroscopic margins along proximal ½-⅔ and acute, attenuate to apiculate apices, with apiculae often falling off and tipped by 1 or 2 teeth, the upper surfaces glabrous, except for few, distal, teeth-like hairs near apices, and with few submarginal to marginal stomata near central portion of basiscopic margins. In addition, its leaf upper surfaces are comprised by rounded to quadrangular, sinuate-walled, papillate cells, each cell lumen with many (i.e., 7-14) papillae, and with margins bordered by elongate, straight-walled, papillate idioblasts on lower leaf surfaces. Finally, its median leaf upper surfaces have marginal to submarginal stomata along proximal ½ of outer margins.
Selaginella papillosa is a member of the "Selaginella deltoides group" as defined by Valdespino (2016). Among species in that alliance it is morphologically close (e.g. in habit, leaf, and overall megaspore sculpturing pattern) to S. aculeatifolia and the here described S. pubimarginata (see for discussion). These three species might, in addition, be sympatric, as they have been collected in the Guiana Highland region of Venezuela at similar low to mid elevations. Selaginella papillosa differs from S. aculeatifolia by its lateral leaf upper surfaces with few (vs. without) submarginal stomata along central, basiscopic portion of the laminae, with 3-5 (vs. many, ca. 50) short hairs or toothlike projections near distal most portion of apices (vs. along distal ½ of basiscopic halves and apices), with midribs inconspicuous (vs. conspicuous, outlined by elongate, straight-walled and papillate idioblasts), and acute to apiculate (vs. long-acuminate) apices. It is further differentiated from the latter by its median leaves broadly ovate to ovate-orbiculate or elliptic (vs. broadly ovate to ovate-elliptic), with oblique and decurrent (vs. oblique or rounded) bases, and stomata present on upper leaf surfaces along distal ½ (vs. ¾) and with few (vs. without) stomata submarginally to marginally along proximal ½ portion of outer margins. Furthermore, its megaspores proximal and distal faces microstructure consists of long-(vs. short-) echinae. Selaginella papillosa was confused in the past with S. brevifolia and, in fact, its type collection was originally identified as the latter species. Selaginella papillosa differs from S. brevifolia by the characters listed in the diagnosis and by its lateral leaf having only very few, i.e., 4-6 tooth-like short hairs near the apices, whereas the latter species has many of these hairs along the basiscopic halves of the laminae and toward the apices.
Selaginella papillosa is also set aside from the similar S. albolineata by its median and lateral leaves upper surfaces without (with many, elongate) idioblasts and acroscopic margins long-ciliate along proximal ½-⅔, otherwise denticulate distally (vs. entire to scarcely denticulate throughout), and median leaf inner margins long-ciliate (vs. denticulate).
The paratype specimen of S. papillosa (Steyermark et al. 130146 at MO) was originally identified as S. revoluta Baker, vel aff., a species that is the center of a species group described by Mickel et al. (2004). Selaginella papillosa is a rather more slender species than S. revoluta and differs further from the latter by its median leaves ovate to broadly ovate to ovate-orbiculate or elliptic (vs. broadly ovate, ovate orbicular to ovate-rhombic) with oblique to decurrent (vs. subcordate) bases, and apices with rather narrow and needle-like (vs. broad and subulate) long aristae, each without (vs. with tooth-like) hairs on its surfaces. Finally, S. papillosa could also be compared to S. hirtifolia Valdespino, which is not morphologically close to it but rather is a member of the S. revoluta group. Selaginella papillosa is easily separated from the latter by its lateral leaf upper surfaces almost completely glabrous (vs. with short, teeth-like hairs along the basiscopic, submarginal region and near apices) and long-aristate (vs. acuminate) median leaf apices with the arista hyaline (vs. with the acumen green). Description. Plants epipetric, terrestrial or epiphytic, moss-like. Stems creeping, stramineous, 2.0-12 cm long, 0.25-0.4 mm diam., not-articulate, not flagelliform or stoloniferous, straw-colored to brownish, 1-or 2-branched, the branches arising at ca. 45° angle. Rhizophores axillary, borne throughout the stems, filiform, 0.1-0.15 mm diam.

Selaginella pubimarginata
Leaves heteromorphic throughout, membranaceous, upper surfaces green, golden brown (in old leaves) or dark brown (in alcohol-preserved specimens), lower surfaces silvery. Lateral leaves distant, spreading, perpendicular to stems or less often slightly ascending, broadly ovate, ovate-deltate or ovate-elliptic, 1-1.5 × 0.5-1.2 mm; bases rounded, glabrous, acroscopic bases slightly overlapping stems, basiscopic bases free from stems; acroscopic margins on both surfaces plane or sometimes revolute on upper surfaces, along proximal ½-⅔ bordered by a hyaline band comprised of idioblasts, the band 1-6 cells wide, the idioblasts elongate, straight-walled, and papillate, the papillae in a single or double row over each cell lumen, long-ciliate, otherwise on distal ⅓-½, greenish, bordered by quadrangular to rounded cells, entire or sparse-and minutely denticulate, especially along distal ⅓, basiscopic margins on both surfaces greenish, bordered by quadrangular to rounded cells, entire throughout or sparse-and minutely denticulate, along distal ⅓; apices attenuate to shortly acuminate, each acumen ca. 0.1 mm long, tipped by 1-3 teeth; upper surfaces mostly glabrous, except for many, short, teeth-like hairs marginally to submarginally along basiscopic margins and distally towards and at the apices, comprising rounded to quadrangular, slightly sinuate, and broad-walled cells on basiscopic ⅔ of the laminae, the cells papillate, the papillae 1-5 and irregularly arranged on each cell lumen, on acroscopic ⅓ of the laminae comprising strongly sinuate, thin-walled, and glabrous cells, without idioblasts, stomata present on acroscopic margins along distal ⅓ and on basiscopic margins along distal ¾, lower surfaces glabrous, comprised of elongate, sinuate-walled, laevigate cells and of straight-walled, papillate idioblasts, the papillae 7-28 in one or two rows on each cell lumen, the idioblasts evenly distributed on the laminae and strongly grouped on proximal, basal region of the laminae, with stomata on 1-5 rows along midribs. Median leaves distant to slightly imbricate near branch tips, ascending, broadly elliptic to orbicular or broadly ovate-elliptic with both inner and outer halves equal in width, 0.7-1.2 × 0.5-0.8 mm; bases glabrous, oblique, not decurrent, without auricles; margins plane or outer margins on proximal ¼ revolute, along proximal ½ bordered by greenish, quadrangular cells, on distal ½ bordered continuously by a narrow hyaline band comprised of idioblasts, the band 1 or 2 cells wide, the idioblasts similar to those in the hyaline marginal bands of proximal ½-⅔ of acroscopic margins of the lateral leaves, dentate on outer margins and short-ciliate along proximal ½, otherwise dentate along distal ½ on inner margins; apices short acuminate, each acumen 0.1 or 0.2 mm long and tipped by 1-3 teeth; upper surfaces glabrous, except for few, submarginal, short, teeth-like hairs on mid portion of outer margins, comprised of round to quadrangular slightly sinuate, thick-walled, papillate cells and one, papillate idioblast along mid-section of outer margins, the papilla 10-13 on a single row on each cell lumen, stomata on midrib along distal ½ and submarginally to marginally along proximal ½ of outer margins, lower surfaces glabrous, comprised of elongate, sinuate-walled, laevigate cells, without stomata. Axillary leaves broadly ovate, ovate-deltate or ovateelliptic, 1.2-1.6 × 0.7-1.2 mm; bases attenuate; margins bordered continuously by a hyaline band comprised of papillate idioblasts along proximal ⅔, the band 1-6 cells wide, the papillae in a single row, on distal ⅓ bordered by greenish, quadrangular cells, long-ciliate along proximal ½-⅔, otherwise entire to denticulate distally; apices attenuate, each 0.1 mm long, tipper by 1-5 teeth. Strobili terminal, loosely quadrangular, 1.5-9 mm long. Sporophylls monomorphic, without a laminar flap, each with a slightly developed keel along midribs, the keel puberulent with short, tooth-like projections distally, ovate to ovate-lanceolate, (0.6)0.9-1.5 × (0.3)0.5-0.7 mm; bases rounded; margins obscurely hyaline bordered by 1-3(4) elongate, papillate idioblasts (especially apically), serrate; apices long-acuminate, tipped by 1-3 teeth; dorsal sporophylls with upper surfaces green and cells as in median leaves, except for the half that overlaps the ventral sporophylls where the surfaces are greenish hyaline to hyaline with elongate and slightly sinuate-walled cells, lower surfaces hyaline and comprising elongate, sinuate-walled cells; ventral sporophylls with both surfaces, hyaline, comprised of elongate, papillate, sinuate-walled cells. Megasporangia few and proximal, along two ventral rows; megaspores light to lemon-yellow, 240-250 µm diam., proximal faces rugulate with a slightly developed equatorial flange, the microstructure sparsely, short echinate and perforate, distal faces rugulate to reticulate, the rugulae or reticulae open (incomplete) to closed, each reticulum with low walls, the microstructure sparsely, short echinate and perforate. Microsporangia light orange in two dorsal rows and distally along two ventral rows; 22-250 µm diam., microspores light orange, rugulate on proximal and distal faces, with the microstructure perforate.
Habitat and distribution. Selaginella pubimarginata grows on shaded or exposed moist boulders, along streambeds, and waterfalls in tropical rainforests at 80-700 m; it is known at and around Cerro Huachamacari, along the rivers Sipapo and Coromoto in Amazonas state, and along Río Caura in Bolívar state, Venezuela.
Etymology. The epithet derives from the Latin "puberulus," slightly pubescent, and "marginatus," having a border. Together these refer to the presence of submarginal hairs on lateral leaves upper surfaces near the basiscopic and apical portion of leaf laminae.
Conservation status. Selaginella pubimarginata is known from four collections made in two states in the Guiana Highland region of Venezuela. Current available data, however, is scanty and does not allow for a reliable conservation assessment. Accordingly, this new species is considered Data Deficient (DD) based on IUCN (2012).
Additional specimens examined ( Discussion. Selaginella pubimarginata is characterized by its moss-like habit, lateral leaf ovate-deltate, with tooth-like, short hairs on the upper surfaces along basiscopic halves of leaf laminae, long-ciliate margins along proximal ½, and acute to attenuate to shortly acuminate apices, axillary leaves similar in overall shape and apices to lateral leaves and long-ciliate margins along proximal ½. Selaginella pubimarginata belongs in the "Selaginella deltoides group", and among species in this alliance it is morphologically close to S. albolineata and S. papillosa. It is set aside from S. albolineata by characters listed in the diagnosis. Selaginella pubimarginata is distinct from S. albolineata by its axillary leaves ovate-deltate (vs. ovate-elliptic) Figure 12. Selaginella pubimarginata Valdespino. A Megaspore, proximal face B detail of megaspore, proximal face C megaspore, distal face D detail of megaspore, distal face E microspore, proximal face F detail of microspore, proximal face G microspore, distal face H detail of microspore, distal face. A-H taken from the holotype. with acute to attenuate to shortly acuminate (vs. obtuse to rounded) apices, lateral leaf upper surfaces without (vs. with many) idioblasts, and median leaf upper surfaces with a single, elongate and papillate idioblast on either the outer or inner halves of the laminae (vs. with two or three, elongate, and papillate idioblasts on the outer and inner halves of the laminae). Selaginella pubimarginata differs most noticeable from the also similar S. papillosa by its median leaf upper surfaces with a single (vs. lacking) elongate and papillate idioblasts on either the outer or inner halves of the laminae, with (vs. lacking) one or two, teeth-like hairs on mid, submarginal portion of the outer half of the laminae, and laminae comprised of rounded, sinuate-walled cells with the cell lumina including 1-5 (vs. 4-15) rounded (vs. conical) and not protruding (vs protruding or elevated) papillae, as well as apices covered by (vs. without) teeth-like, short hairs. In addition, the lateral leaf upper surfaces of S. pubimarginata are covered by many (vs. few) ca. 40 (vs. 3-5) short hairs or teeth-like projections along submarginal portion of basiscopic margins and on distal, apical portion (vs. concentrate on distal most portion) of apices. Finally, S. pubimarginata is further distinct from S. papillosa by its rugulate (vs. rugulate-reticulate) megaspores on proximal faces with a slightly developed (vs. with a well-developed) equatorial flange, with microstructure sparsely (vs. abundantly) covered by short-(vs. long-) echinae and distal faces slightly (vs. strongly) reticulate with open (vs. with open and closed) reticulae delimited by low (vs. high) muri.
All specimens of S. pubimarginata here cited were previously identified either as S. brevifolia or S. brevifolia vel aff. Selaginella pubimarginata is set aside from S. brevifolia by its median leaf ovate-orbicular to orbicular (vs. ovate) with the laminae almost as wide as long (vs. longer than wider) with outer and inner leaf halves about the same width (vs. outer leaf half frequently wider than the inner leaf half ), attenuate to shortly acuminate (vs. long-aristate) apices, each acumen ⅕-¼ (vs. ⅓-½) the length of the leaf lamina, and margins obscurely hyaline or greenish (vs. conspicuously hyaline, especially the outer margin). Selaginella pubimarginata differs further from S. brevifolia by its lateral leaf upper surfaces when viewed with a dissecting scope with midribs not marked and of the same color as the laminae (vs. well-marked and straw-colored) and laminae epidermal cells inconspicuously (vs. conspicuously) rounded, and long-ciliate along proximal ½ (vs. ½-¾) margins.
Description. Plants epipetric or terrestrial, ribbon-like, with leafy liverwort habit. Stems creeping, stramineous, 3-10 cm long, (0.1)0.18-0.34 mm diam., non-articulate, not flagelliform, non-stoloniferous, 1-or 2-branched, the lateral branches resulting from division of the main stem usually becomes arrested. Rhizophores axillary and subdorsal, borne throughout stems, 0.08-0.12 mm diam. Leaves heteromorphic throughout, chartaceous to thin-coriaceous, upper surfaces green or light-brown when old or due to dying process, lower surfaces silvery green or light-brown when old or due to dying process. Lateral leaves distant, ascending to slightly perpendicular to stems, broadly elliptic to broadly ovate, 0.7-2.0 × 0.4-1.4 mm; bases rounded to roundtruncate, glabrous, acroscopic bases overlapping stems, basiscopic bases free from stems; acroscopic margins on upper surfaces greenish or weekly hyaline along proximal ½, otherwise greenish on distal ½, composed of quadrangular to rounded cells, basiscopic margins on upper surfaces greenish, bordered by quadrangular to rounded cells, margins on lower surfaces continuously bordered by a hyaline band comprised of idioblasts, the band 3-15 cells wide, the idioblasts elongate, straight-walled, and papillate, the papillae in a single row over each cell lumen, acroscopic margins dentate to denticulate throughout or denticulate along proximal ⅓−½ and entire distally, basiscopic margins sparsely denticulate or entire throughout; apices obtuse to rounded, occasionally tipped by a caducous short or tooth-like hair; upper surfaces glabrous, comprising rounded to irregularly, sinuate-walled, laevigate cells, without idioblasts or stomata; lower surfaces comprising elongate, slightly sinuate-walled cells, without idioblasts, with stomata in 1-3 rows along midribs. Median leaves slightly imbricate to distant, ascending, ovate to ovate-deltate with the inner halves of the leaf lamina ⅛−¼ wider than the outer halves, 0.6-1.5 × 0.4-1.0 mm; bases glabrous, cordate to subcordate, without auricles; margins bordered continuously by a hyaline band comprised of idioblasts, the band 2-5 cells wide, the idioblasts, elongate, straight-walled, and papillate, the papillae on one row on each cell lumen, denticulate throughout or entire along proximal ½ and denticulate along distal ½; apices keeled, long-acuminate to long-aristate, the acumen or arista denticulate, ⅓-¼ the length of the laminae, each (0.06-)0.1-0.2 mm long, usually tipped by one to three teeth; upper surfaces similar to lateral leaves upper surfaces, without idioblasts, with stomata in 1 or 2 rows restricted to distal ⅓ along the keel; lower surfaces similar to lower surfaces of lateral leaves, without idioblasts or stomata. Axillary leaves shape (except, occasionally oblong), size, bases, margins, apices and leaf surfaces similar to lateral leaves. Strobili terminal, single or dichotomous at branch tips, loosely quadrangular to slightly dorsiventral flattened, 2-12 mm long. Sporophylls slightly heteromorphic, broadly ovate to ovate-lanceolate (ventral sporophylls more broadly ovate and slightly shorter, dorsal sporophylls usually ovate-lanceolate and slightly larger), with a strongly developed keel along midrib, the keel glabrous, 1.0-1.3 × 0.5-0.9 mm; bases rounded; margins bordered by a hyaline band similar to that of the median leaves, dentate; dorsal sporophylls spreading, strongly keeled along midribs and especially near apices, the keel glabrous; apices acute to short-acuminate and beveled in profile and abruptly ending in a short, tooth-like cilia, the cilia often caducous; upper surfaces green and cells as in median leaves, except for the half that overlaps the ventral sporophylls where the surfaces are hyaline composed of idioblasts similar to those of the median leaves margins, lower surfaces hyaline and comprising elongate, sinuate-walled cells; ventral sporophylls ascending, slightly keeled along midribs, the keel glabrous; apices acute to short-acuminate, not beveled in profile and usually ending in a short cusp; upper and lower surfaces hyaline, comprised of idioblasts similar to those of the median leaves margins. Megasporangia along two ventral rows; megaspores lemon yellow, 200-220 µm diam., proximal faces rugulate-reticulate with a well-developed equatorial flange, the microstructure echinate and perforate, distal faces reticulate, the reticulae open (incomplete) to closed, the microstructure granulose and perforate; microsporangia on two dorsal rows; micropores light-orange, 30-35 µm diam., proximal and distal faces gemmate, the microstructure granulose.
Habitat and distribution. Selaginella rostrata grow on wet and mossy sandstone bluffs, near damp stream banks, and at the base of waterfalls in mountainous tropical rainforests at 1000-2130 m. It has been found on several tepuis of the Guiana Highland in the state of Bolívar, Venezuela.
Etymology. The specific epithet derives from the Latin "rostratum," meaning beaked, and refers to the keeled/beaked median leaf and dorsal sporophyll apices.
Conservation status. Selaginella rostrata is known from several collections made over a time span of more than fifty years from mid-to-late twentieth century at different localities in the Guiana Highland region of Venezuela, some of which are adjacent to the neighboring country of Guyana. This suggests an overall wide distribution. Unfortunately, the paucity of more recent collections due, in part, to a decline in botanical exploration in the aforementioned areas, does not allow for an accurate conservation assessment. Consequently, this new species is considered Data Deficient (DD) based on IUCN ( Discussion. Selaginella rostrata is characterized by its creeping, ribbon-like, leafy liverwort habit, median leaf ovate to ovate-deltate, with inner halves of leaf laminae ⅛−¼ wider than outer halves, margins continuously bordered by a hyaline band of idioblasts, each band 2-5 cells wide, the idioblasts elongate, straight-walled, and papillate, and dentate to denticulate, and apices strongly keeled, long-acuminate to long-aristate, the acumen or arista denticulate, ¼−⅓ the length of the laminae, each (0.06)0.1-0.2 mm long, each usually tipped by one to three teeth. Selaginella rostrata its further defined by lateral leaf broadly elliptic to broadly ovate with obtuse to rounded apices, which occasionally are tipped by a caducous short or tooth-like hair, and sporophylls (especially dorsal sporophylls) conspicuously keeled (i.e., carinate) along midribs, and with apices acute with those of dorsal sporophylls apiculate ending on a single toothlike, short hair, and stomata along midribs and keeled apices.
Selaginella rostrata is morphologically close to a species group that I informally call the "S. microdonta group," and in particular to the latter species and S. neblinae. Selaginella rostrata can be distinguished from S. microdonta, which may still need to be further circumscribed, by the characters listed in the diagnosis and its median leaf with inner halves of leaf laminae ⅛−¼ wider than outer haves (vs. inner and outer halves of leaf laminae about the same width or inner halves ⅛ narrower than outer halves). Selaginella rostrata further differs from S. microdonta by its acroscopic lateral leaf margins dentate to denticulate throughout or denticulate along the proximal ⅓−½, and entire distally, and basiscopic margins sparsely denticulate or entire (vs. acroscopic and basiscopic margins serrate). Furthermore, S. rostrata is also set aside from S. neblinae by its broadly elliptic to broadly ovate (vs. ovate-lanceolate) lateral leaves, with obtuse to rounded (vs. long attenuate to acuminate) apices, each occasionally tipped by a caducous short or tooth-like hair (vs. hair or teeth absent), and median leaf apices acuminate to long-aristate, each acumen or aristae ¼-⅓ (vs. ½) the length of the laminae, and margins conspicuously hyaline (vs. greenish).
Selaginella microdonta, S. rostrata, and S. neblinae along with S. breweriana, S. cardiophylla, S. hemicardia, and S. valdepilosa are part of the S. microdonta group. The relationship of the "S. valdepilosa group" still needs to be ascertained by phylogenetic methods but an initial hypothesis would suggest that S. breweriana and S. neblinae seem to be sister species, whereas S. cardiophylla and S. rostrata form another putative sister alliance that in turn is sister to a S. microdonta and S. hemicardia alliance, to which probably S. valdepilosa also belongs to as an offshoot that is most distinct by its leaves and sporophylls densely, long-ciliate.
Interestingly and as part of this study, it was observed that branches of S. rostrata can become arrested at branch forks giving the species a ribbon-like, leafy liverwort resemblance. Valdespino (1992) previously reported this condition as resting branches in S. hemicardia. Furthermore, as a result of the undeveloped branches, rhizophores in both species are seemingly subdorsal.
Additionally, one paratype collection here cited (i.e., Lierner & Holsts 20424 p.p. at MO and UC) represents mixed gatherings, which I identified as a = S. rostrata and b = S. tuberculata, while two other collections (Steyermark et al. 92588 p.p. at U, and Steyermark et al. 92588-A p.p at U) are also mixed gatherings, which I identified as a = S. rostrata and b = S. cardiophylla). Selaginella tuberculata also has a leafy, liverwort habit and creeping stems and might eventually prove to be part of the "S. microdonta group," but it is distinct from the rest of species here included in that alliance by its acroscopic lateral leaves margins long-ciliate along the proximal ¼−⅓ with upper sur-faces puberulent along the basiscopic halves and towards the apices as well as occasionally also distally along the acroscopic halves.

Key to the
Description. Plants terrestrial. Stems erect, stramineous, 28-60 cm tall, (0.5)1.0-2.5 mm diam. on main stem before first branches, non-articulate, not flagelliform, stoloniferous, 2 or 3-branched, the terminal portion of the stem similar in shape to lateral branches (i.e., conform). Rhizophores axillary, ventral, dorsal, and seemingly lateral, borne on lowermost part of the stems and throughout stolons, stout, 0.2-0.5 mm diam. Leaves seemingly monomorphic and strongly appressed to the stems up to shortly before (ca. 3 cm below) first branch, then heteromorphic throughout, coriaceous, upper surfaces shiny greenish yellow (i.e., citrine) when dry, smooth to slightly striate, lower surfaces shiny to silvery greenish-yellow, striate submedially and smooth towards margins, those on main stems before fully heteromorphic ovate-deltate or deltate, the bases prominently raised and truncate with both edges rounded or slightly subcordate and entire or denticulate, the margins narrowly to broadly hyaline, greenish-hyaline or greenish, inner margins shortciliate along proximal ¼, otherwise dentate to denticulate distally, outer margins dentate to denticulate distally, apices acute, tipped by 1-4 teeth or entire. Lateral leaves on main stem after leaves fully heteromorphic, imbricate and ascending up to proximal ½ of the stems, otherwise distant and spreading along distal ½ of the stems, ovate to broadly ovate ascending, 4.0-6.0 × (1.5)2.0-3.5 mm; bases rounded to subcordate with a truncate and prominent central portion, glabrous, acroscopic bases strongly overlapping stems, rounded, basiscopic bases free from stems, rounded; margins on upper surfaces narrowly bordered by greenish, rectangular, and laevigate cells, acroscopic margins on lower surfaces bordered continuously by a hyaline band comprised of idioblasts, the band 2-7 cells wide, the idioblasts elongate, straight-walled, and papillate, the papillae in a single row over each cell lumen, basiscopic margins on proximal ⅓ bordered by elongate, greenish, rectangular, and laevigate cells and submarginally bordered by a hyaline band comprised of idioblasts, the band 1-5 cells wide, the idioblasts elongate, straight-walled, and papillate, the papillae in a single row over each cell lumen, on distal ⅔ bordered by a hyaline band comprised of idioblasts, the band 3-10 cells wide, the idioblasts similar to those of the acroscopic margins and submarginal proximal ⅓ of basiscopic margins and often specially toward distal ⅓ intermixed with cells similar to those of basiscopic proximal ⅓; apices acute to shortly attenuate, tipped by 1-3 teeth; upper surfaces comprising irregularly shaped, somewhat rectangular to quadrangular, sinuate-walled cells, with some sparingly distributed short, quadrangular to round, papillate idioblasts, each idioblast cell lumen with 5-8 papillae, without stomata, lower surfaces comprised of elongate, sinuate-walled cells and of elongate, straight-walled, papillate idioblasts, each idioblast cell lumen with 8-45 papillae in 1-3 rows, stomata on 1-6 rows along midribs. Median leaves on main stem after leaves fully heteromorphic, distant, ascending, broadly ovate, ovate-elliptic or ovate-lanceolate, 2.0-4.0 × 1.3-2.0 mm; bases glabrous, subcordate with a prominent, round outer lobe, without auricles; inner margins on upper surfaces bordered continuously by a narrowly hyaline band of idioblasts along distal ¾, the band 1-4 cells wide, the idioblasts similar to those in the hyaline marginal bands of lateral leaves acroscopic margins on lower surfaces of lateral leaves, the outer margins on upper surfaces obscurely greenish and comprising elongate, straight-walled, glabrous cells along proximal ⅓-½, on proximal ⅓-½ submargins and distal ½-⅔ margins bordered continuously by a hyaline band of idioblasts, the idioblasts similar to those in the hyaline marginal bands of lateral leaves acroscopic margins on lower surfaces but the band 2-7 cells wide and with one or two rows of papillae on cell lumen, entire along proximal ⅓ and shortly ciliate along distal ⅔; apices acuminate to short-aristate, each acumen or arista 0.1-0.3 long, tipped by 1-3 teeth; upper surfaces comprising quadrangular, rectangular to roundish, sinuate-walled cells and many, evenly distributed papillate idioblasts, each idioblasts with 5-12 papillae, stomata in 1-4 rows on distal ⅔-¾ along the midribs and marginal to submarginal along proximal ⅓ of outer margins, lower surfaces comprising elongate, straight-walled cells, without idioblasts, ex- cept for idioblasts present along proximal submarginal portion of outer margins where the idioblast are similar to those on distal ½-⅔ of outer margin on upper surfaces, without stomata. Axillary leaves on main stem after leaves fully heteromorphic similar in shape to lateral leaves or narrowly ovate, 3.5-4.4 × 1.5-2.4 mm; bases similar to those of lateral leaves; margins on upper and lower surfaces as those in margins of lateral leaves; apices as those of lateral leaves; both surfaces similar to those of lateral leaves. Strobili terminal on branch tips, quadrangular, 0.4-1.0 cm long. Sporophylls monomorphic, without a laminar flap, each with a slightly developed keel along midribs, the keel glabrous or with few, short, tooth-like projections distally, ovate-lanceolate, 1.4-2.0 × 0.5-1.0 mm; bases rounded; margins narrowly hyaline, 1 or 2 cells wide with the cells elongate, slightly sinuate-walled and glabrous, parallel to margins, shortly ciliate along proximal ½, denticulate on distal ½ or denticulate throughout; apices long-attenuate to long-acuminate, the acumen 0.1 or 0.2 mm long, tipped by 1 tooth; dorsal sporophylls with upper surfaces green and cells as in median leaves, except for the half that overlaps the ventral sporophylls where the surfaces are greenish hyaline with elongate and slightly sinuate-walled cells, lower surfaces silvery green and comprising elongate, sinuate-walled cells; ventral sporophylls with both surfaces, silvery green to hyaline, comprised of elongate, papillate, sinuate-walled cells. Megasporangia few on two proximal ventral rows; megaspores yellow, 100-120 µm diam., proximal faces rugulate-reticulate with a well-developed equatorial flange, the microstructure perforate and echinate, distal faces reticulate, the reticula closed, the microstructure granulate and perforate. Microsporangia on two dorsal rows and along most of two ventral rows; microspores light orange, 25-30 µm diam., proximal faces rugulate, the microstructure echinate and perforate, distal faces capitate, with each caput microechinate, the rest of the microstructure echinate and perforate.
Habitat and distribution. Selaginella xanthoneura grows in tropical montane rainforests at 1800-2300 m. It is known from Serranía del Perijá, an extension of the eastern Andean branch (Western Cordillera) in the state of Magdalena, and in the isolated mountain range of Sierra Nevada de Santa Marta, states of César and Magdalena, both in northern Colombia, and is expected to also occur in the neighboring state of Zulia, Venezuela. It has been collected in fertile condition from February to June.
Etymology. The specific epithet derives from the Gr. "xanthos," yellow, and "neuron," nerve, referring to the conspicuous yellow, leaf midribs on upper surfaces.
Conservation status. Selaginella xanthoneura is known from only six collections made in two adjacent Colombian Departments, growing at high elevations, probably in and around protected areas, which however are imperiled by human encroachments and natural adversities such as landslides. It might eventually prove to be present in adjacent areas in Venezuela, but there is no current documentation to support this. It might well be that this species is relatively well protected, but the limited number of documented occurrences and distribution, as well as possible threats enumerated above indicate that it should be considered Vulnerable (VU) based on IUCN (2012).  Manaure, Serranía del Perijá El Cinco, Finca Vistahermosa, SE de la carretera, 10°26'N, 72°57'W, 2200m, 13 Nov 1993, Rangel et al. 11420 (COL-image), 2235m, 14 Nov 1993 Discussion. Selaginella xanthoneura is characterized by its fern-like habit, erect stems, each 28-60 cm tall, leaves on main stems shortly (ca. 3 cm) before first branches seemingly monomorphic and strongly appressed, the leaves after becoming fully heteromorphic with shiny, greenish yellow (i.e., citrine) upper surfaces when dry and yellowish to stramineous midribs. It is further distinguished by its median leaf bases subcordate with a prominent, round outer lobe, outer margins along proximal, submarginal ⅓-½ and distal, marginal ½-⅔ continuously bordered by a hyaline band of idioblasts, and acuminate to short-aristate apices, the upper surfaces of median leaves and the lower surfaces of lateral leaves with papillate idioblasts, and relatively short strobili, each 0.4-1.0 cm long, and with few megasporangia restricted to proximal portion of two rows of strobili ventral sporophylls.
Interestingly, one examined duplicate specimens of S. xanthoneura (Schultze 1518, B) has vegetative growth from strobili tips. This is a feature that has been amply documented in other morphologically related members of the "Selaginella flabellata group," as well as on unrelated taxa from different regions of the world (Hieronymus 1901;Williams 1931;Jermy 1990;Valdespino 1993aValdespino , 1993bValdespino 1995;Zhang et al. 2014;Valdespino et al. 2015) and for which specific patterns were described (Valdespino et al. 2015). This same collection (Schultze 1518) at B and BM was originally determined by Alston as S. hartii, which certainly is somewhat similar to S. xanthoneura because of their overall fern-like habit with erect stems and leaves fully dimorphic shortly before first stem branches. Selaginella xanthoneura is easily set aside from the latter species by characters listed in the diagnosis. In addition, S. xanthoneura, at present, is only known to occur in Colombia, whereas S. hartii is only known from Trinidad and Tobago and the Peninsula of Paria in Sucre state, Venezuela. Furthermore, S. xanthoneura has a more robust plant habit with stems 2 or 3-(vs. 1 or 2 or occasionally 3-) branched.
Selaginella xanthoneura, as well as other members of the "Selaginella flabellata group," such as S. cheiromorpha Alston, S. hartwegiana Spring, and S. mosorongensis Hieron. all have similar median and lateral leaf shapes. Nevertheless, S. xanthoneura differs from all those species by its median leaf outer bases lacking a distinct auricle and having conspicuously yellow to yellowish lateral and median leaf midribs. Selaginella xanthoneura is further set aside from S. mosorongensis by its entire (vs ciliate) median leaf outer bases. Description. Plants terrestrial. Stems erect, stramineous, (25)35-75 cm tall, 1.2-3.0 mm diam., non-articulate, usually not flagelliform or infrequently so, stolonifer-ous, 3-branched, the terminal portion of the stems similar in shape to lateral branches (i.e., conform). Rhizophores axillary, ventral, dorsal, dorso-axillary, and seemingly lateral, borne on lower most part of stems and throughout stolons, filiform or stout, 0.2-1.0 mm diam. Leaves seemingly monomorphic and strongly appressed to the stem shortly before or after the first or second branches and without distinctive auricles, then heteromorphic throughout, chartaceous to coriaceous, upper surfaces shiny dark, brown-green (dark olive) to brownish (due to drying technique), seemingly smooth, lower surfaces shiny, yellowish green, dark olive to brown (due to drying technique), smooth. Lateral leaves on main stem after leaves become fully heteromorphic, distant, ascending to slightly spreading, ovate or ovate-oblong, 3.0-4.8 × 1.4-2.6 mm; bases rounded to truncate, glabrous, without auricles, acroscopic bases strongly overlapping stems, basiscopic bases free from stems; margins on upper and lower surfaces bordered by a narrow band comprised of greenish cells, the band 1-3 cells wide, the cells elongate, slightly sinuate-walled, and glabrous, on acroscopic margins dentate along proximal ¼, otherwise denticulate on distal ¾, on basiscopic margins entire along proximal ¾, otherwise sparsely denticulate distally; apices broadly acute to obtuse, tipped by 3-5 teeth; upper surfaces consisting of quadrangular to rectangular (jigsaw puzzle-like), sinuate-walled cells (often difficult to distinguish because of waxy deposits), many of these consisting of papillate idioblasts, comprising some sparse, elongate and papillate idioblasts, the papillae 4-11 in 1 or 2 rows on each cell lumen, without stomata; lower surfaces consisting of elongate, irregularly sinuate-walled cells (jigsaw puzzle-like) and of many elongate, straight-walled, papillate idioblasts, papillae 4-11 in 2 rows on each cell lumen, with stomata on 2-4 rows along central portion of midribs Median leaves on main stem after leaves fully heteromorphic, imbricate, ascending, ovate, ovate-elliptic, ovate-lanceolate to ovateoblong, 1.7-4.2 × 0.8-2.8 mm; bases glabrous, oblique, truncate or asymmetric, inner bases rounded to truncate, outer bases auricled, the auricles ciliate with 3-14 short hairs; margins bordered continuously by a band of glabrous cells, the band 1-3 cells wide with the cells elongate, slightly sinuate-walled, glabrous, except for those on distal ⅓ of outer margins that are composed by a narrow hyaline band of idioblasts, the band 1-3 cells wide, the idioblasts straight-walled, and papillate, the papillae in one row, margins dentate to denticulate; apices acute, acuminate or aristate, each acumen or arista 0.1-0.6 mm long, tipped by 1-3 teeth; upper surfaces similar to those on upper surfaces of lateral leaves, except abundantly covered by quadrangular and elongate and papillate idioblasts, the papillae 4-32 in 1 or 2 rows on each cell lumen, with stomata in 1-5 rows along the midribs, lower surfaces comprising by elongate, irregularly sinuate-walled cells, (jigsaw puzzle-like), without idioblast and stomata. Axillary leaves on main stem after leaves fully heteromorphic ovate to ovate-lanceolate, 2.0-4.0 × 0.8-2.2 mm; bases rounded to slightly truncate, entire, without auricles; inner and outer margins as acroscopic margins of lateral leaves, denticulate throughout; apices broadly acute to obtuse, tipped by 1-4 teeth; both surfaces as lateral leaves. Strobili terminal on main stem and each branch tip, quadrangular, 0.5-4.0 cm. Sporophylls monomorphic, without a laminar flap, each with a slightly developed and glabrous keel along distal ¾ of the midrib, ovate to ovatelanceolate, 0.8-1.2 × 0.4-0.7 mm; bases rounded; margins narrowly hyaline, 1 or 2 cells wide with the cells elongate, slightly sinuate-walled and glabrous, parallel to margins, denticulate throughout; apices shortly acuminate, the acumen 0.1-0.2 mm long, tipped by 1-3 teeth-like projections; dorsal sporophylls with upper surfaces green and cells as in et al. (2017), a number of specimens from Colombia and Venezuela are known and here newly documented. The study of these broader spectrum of specimens provides a better understanding of morphological characters (including mega-and microspores ornamentation features) of the species, expanded geographic circumscription, as well as of its presumed affinities. Consequently, an emended description for S. surucucusensis is provided, including a novel illustration.
Selaginella surucucusensis is characterized by its fern-like habit, non-articulate and usually not flagelliform or infrequently so, stoloniferous, 3-branched erect stems, each (25)35-75 cm tall and 1.2-3.0 mm in diam., with axillary, lateral, and dorsal to dorsoaxillary rhizophores, which are borne on the lower most part of the stems and throughout stolons, each filiform or stout, 0.2-1.0 mm diam. In addition, the leaves on main stems are seemingly monomorphic and strongly appressed to stems, shortly below or above first stem branches and after this become fully heteromorphic, with median leaf upper surfaces covered with short-elongate or punctate, papillate idioblasts, and with a small or reduced, dentate outer auricle on outer bases, and lateral leaf with scattered, elongate, papillate idioblasts on lower surfaces. Furthermore, megaspores of this species are white, rugulate-reticulate on proximal faces without an equatorial flange and with strongly echinate and perforate microstructure, reticulate with open and closed reticulae formed by low muri and reticulate-granulose on distal faces with strongly echinate and perforate microstructure. Finally, microspores of this species are orange, echinate, rugulate, and granulate on proximal faces with punctate microstructure, capitate or baculate on distal faces with each caput or bacula and the rest of the surface with an echinate microstructure. In addition, the most examined specimens of S. surucucusensis have their leaf upper surfaces dark, brown-greenish to brownish, probably due to being fixed in alcohol.
Selaginella surucucusensis is morphologically somewhat similar to S. gioiae, from which it is set aside by the characters listed under the diagnosis and discussion of the latter. Furthermore, because of the fern-like habit and erect stems of S. surucucusensis most examined specimens were variously misidentified as S. anceps (C. Presl) C. Presl, S. amazonica Spring, S. mazaruniensis Jenm., S. oaxacana Spring or S. palmiformis. The short-elongate or punctate, papillate idioblasts on upper surfaces in median leaf of S. surucucusensis are somewhat similar to those of S. cuneata Mickel & Beitel from Mexico. Selaginella surucucusensis differs from S. cuneata by its ovate or ovate-oblong (vs. broadly ovate to ovate-orbicular) lateral leaves; median leaves bases (on main stems after first branches) oblique, truncate or asymmetric with the outer bases prominent (vs. slightly so) with (vs. without) an outer auricle, outer halves of leaf laminae at least ¼ to ½ wider (vs. twice as narrow) than inner halves, and margins of median and acroscopic margins of lateral leaves hyaline (vs. greenish).
Selaginella surucucusensis also appears morphologically close to S. oaxacana because both have median leaf with acuminate to short-aristate apices, narrowly hyaline and denticulate margins, outer basal auricles, and axillary, lateral, and dorsal rhizophores. Selaginella surucucusensis is set aside from S. oaxacana by its lateral leaf basiscopic bases rounded to adnate to the stems (vs. geniculate to auricled) and upper surfaces of the median leaves and sporophylls with short-elongate or punctate (vs. with long) idioblasts.
Selaginella surucucusensis differs from S. amazonica by its upper surfaces of leaf shiny, dark brown-green (vs. dark olive) to brownish (due to drying technique) and smooth (vs. dark brown and corrugate), with (vs. without) punctate or elongate idioblasts, median leaves above first branches ovate, ovate-elliptic, ovate-lanceolate to ovate-oblong (vs. broadly ovate to ovate-deltate) with (vs. lacking) an outer auricle, and lateral leaves shortly below or immediately above first branches ovate to ovate-oblong (vs. ovate-deltate). Selaginella surucucusensis is easily set aside from S. anceps by its leaf on main stems seemingly monomorphic and strongly appressed to the stem shortly before or after the first or second branches (vs. up to the third of fourth) branches, truncate and without (vs. with one or two, long, incurved, and ciliate) auricles. Likewise, S. surucucusensis is separated from S. mazaruniensis by its median leaf upper surfaces smooth (vs. corrugate), those above first branch with (vs. without) short-elongate or punctate, papillate idioblasts, with an outer (vs. lacking) auricle, and branches distinctly pinnate and conform (vs. usually flabelliform). Crabbe and Jermy (1973: 141) cited one specimen here included in S. surucucusensis (Schultes & Cabrera 16471, US) as a paratype of S. palmiformis and Alston et al. (1981: 256) followed them. Both species are similar in having their median leaf bases with an outer, ciliate auricle. Nevertheless, in S. palmiformis the auricle is less prominent and covered only by 3-6 hairs. Selaginella surucucusensis further differs from S. palmiformis by its stems 3-(vs. 1-or 2-) branched, rounded when dry (vs. quadrangular) with the overall shape of proximal branches wider at base (vs. at middle) and rhombic-triangular to deltate-triangular (vs. elliptic or elliptic-lanceolate), leaves obviously heteromorphic above first or second (vs. usually at or above fourth) branches with upper surfaces having (vs. lacking conspicuous) short-elongate or punctate, and papillate idioblasts. It differs further from the latter by median leaf margins denticulate (vs. coarsely dentate), truncate (vs. often subcordate) axillary leaf bases, and ovate-lanceolate to ovate-oblong (vs. oblong) lateral leaves. Selaginella surucucusensis further differs from S. palmiformis by its median leaves on main stems after fully heteromorphic ovate, ovate-elliptic, ovate-lanceolate to ovate-oblong (vs. broadly ovate to ovate-deltate) with arcuate (vs. straight and almost central) midribs, outer halves of leaf laminae ca. ⅛ wider than inner halves (vs. both halves about the same width), and leaf bases evenly raised (vs. centrally ventricose).
Selaginella surucucusensis as well as S. altheae Valdespino are members of the "Selaginella flabellata group," and have similar microspore ornamentation but they diverge on their leaf shapes. Selaginella surucucusensis differs from S. altheae by its median leaf margins denticulate (vs. inner margins short ciliate along proximal ⅔, otherwise denticulate on distal ⅓ and outer margins entire along proximal ⅓, becoming short-ciliate along medial ⅓, otherwise denticulate on distal ⅓), with (vs. without) an outer basal auricle, and lacking marginal to submarginal stomata (vs. stomata present on proximal ¼ along outer margins), and lateral leaf acroscopic margins dentate along proximal ¼, otherwise denticulate on distal ¾ (vs. long-ciliate along proximal ½-¾, otherwise short-ciliate to dentate distally).
Finally, the presence of dorsal rhizophores in S. altheae, S. oaxacana, S. surucucusensis, and other members of the "Selaginella flabellata group" might eventually prove to be a morphological character that helps define this alliance. Nevertheless, dorsal rhizophores are also found in other heterophyllous Selaginella species such as S. psittacorhyncha (Valde-spino 2017b) within subg. Stachygynamdrum, where it has not been widely reported, and is characteristic of articulate species of subg. Gymnogynum s.l. (Valdespino et al. 2018;Valdespino and López 2019), subg. Lepidophyllae (Weststrand and Korall 2016), and homophyllous species classified in subg. Rupestrae (Valdespino 1993a;Weststrand and Korall 2016). Consequently, it might well be that dorsal rhizophores are underreported in subg. Stachygynandrum and of wider occurrence in Selaginella or perhaps this feature has originated several times in different evolutionary lineages within the genus. Accordingly, the occurrence of dorsal rhizophores within Selaginella warrants further morphological, anatomical, molecular, and phylogenetic studies throughout species alliances to ascertain its evolutionary implications.