Novel fern- and centipede-like Selaginella (Selaginellaceae) species and a new combination from South America

Abstract Two new Selaginella species (i.e. S. altheae Valdespino and S. squamulosa Valdespino) and a novel combination [i.e. S. philipsonii (Jermy & Rankin) Valdespino] from South America are proposed. Descriptions, illustrations (line drawings and scanning electron micrographs, SEM, images), discussion on taxonomic affinities and information on habitat, distribution and phenology, as well as on conservation status are provided for each. Selaginella altheae is morphologically similar to species with erect, fern-like habit placed in the “Selaginella flabellata (L.) Spring group” as defined by Hieronymus, while S. squamulosa is allied to a species assembly with centipede-like habit here informally termed the “Selaginella vernicosa Baker group;” whereas S. philipsonii with its moss-like habit may be associated with species in the “Selaginella jungermannioides (Gaudich.) Spring group” or those centered on S. ovifolia Baker. All taxa here proposed are classified in subg. Stachygynandrum.


Introduction
Continued work on South American Selaginella leads to the description of two new taxa: Selaginella altheae Valdespino and S. squamulosa Valdespino and to raise to species level S. philipsonii (Jermy & Rankin) Valdespino. These three species are anisophyllous either throughout the stems or shortly below or after the first branches with the leaves arranged in four (i.e. two median and two lateral) distinct ranks and quadrangular strobili composed of monomorphic sporophylls. Accordingly, they can be placed within subg. Stachygynandrum (P. Beauv.) Baker following Jermy's (1986Jermy's ( , 1990) morphologybased classification or that of Weststrand and Korall (2016) supported by phylogenetic analysis using molecular and morphological characters. Alternatively, they could each be assigned to two or three subgenera (i.e. Ericetorum, Stachygynandrum and Heterostachys) proposed by Zhou and Zhang (2015). It is believed, however, that placement of these three species in subg. Stachygynandrum best reflects their morphology, allows for easy identification and facilitates comparison with other taxa.
Selaginella altheae has a fern-like habit with erect main stems and axillary, ventral, dorsal and, occasionally, lateral rhizophores. Morphologically, this species belongs to the "Selaginella flabellata (L.) Spring group" as defined by Hieronymus (1901: 682), which contains ca. thirty-five species in the Americas (Valdespino, unpublished). Selaginella squamulosa seems morphologically related to a species group comprising about seven taxa including S. arrecta A.R. Sm., S. marahuacae A.R. Sm., S. roraimensis Baker, S. scalariformis A.C. Sm. and S. vernicosa Baker and the newly described S. psittacorhyncha Valdespino (Valdespino 2017), which together are herein informally termed the "Selaginella vernicosa Baker group". This group is defined by its centipedelike habit (i.e. plant body elongated and flattened, branching in one plane with leaves suggestive of body segments; overall reminiscent of centipedes), creeping or ascending to suberect stems and coriaceous leaves. Selaginella philipsonii has a moss-like habit (i.e. resembling a pleurocarpous moss in its long-creeping main stems and short lateral branches that often bear reproductive structures), axillary and dorsal rhizophores and small leaves. It may be related to species in the "Selaginella jungermannioides (Gaudich.) Spring group", as circumscribed in Valdespino et al. (2015), or to a species group akin to S. ovifolia Baker.
These additions to Neotropical Selaginella yield the 100 species estimated by Valdespino (2015Valdespino ( , 2016 for Venezuela and raises the number of native Brazilian taxa to 84, including S. psittacorhyncha and the recently recorded S. anaclasta Alston ex Crabbe & Jermy in Serra do Aracá, Brazil (Barbosa-Silva et al. 2016), based on Labiak et al. 5639 (NY!). Thus, Brazil is now the country with the second highest Selaginella diversity in the New World. In the case of Colombia, more studies are still needed to ascertain its Selaginella diversity. It is likely that the number of Colombian species will be greater than that reported by Alston et al. (1981).

Material and methods
Herbarium studies were carried out by examining specimens from BM, CAS, COL, F, GH, MO, NY, OXF, P, PMA, RB, UC, US and W, as well as digitized images from COL and RB (herbarium acronyms follow Thiers 2017). Scanning electron microscopy (SEM) micrographs were made from selected specimens to document leaf surfaces and mega-and microspores sculpturing patterns, when available, from designated types and paratypes. These studies were conducted according to standard techniques as described by Valdespino (1995) and viewed and digitized at different magnifications using a Zeiss Model Evo 40 SEM at 10-20 kV at the Smithsonian Tropical Research Institute (STRI) in Panama. Digitized SEM images were post-processed and assembled in multipart figures using Adobe Photoshop as explained in Valdespino (2016).
Terminology and measurements of leaves and spores, as well as species conservation status provided in descriptions were assessed following Valdespino (2016 and references therein). Countries, in the additionally examined specimens section, were cited according to geographical order.

Taxonomy
Selaginella altheae Valdespino, sp. nov. urn:lsid:ipni.org:names:77173690-1 Figures 1-5 Diagnosis. Selaginella altheae differs from S. lechleri Hieron. by the main stem leaves becoming obviously dimorphic above or 1-4 cm (vs. 3-6 cm) below the first branches of the stems, its lateral leaves bases oblique with a seemingly inner [actually it is an acroscopic] (vs. lacking) auricle that is tufted with 3-15 hairs (vs. bases glabrous) and the axillary leaves rounded to cordate or truncate with two, distinct, incurved and ciliate (vs. lacking) auricles at least up to the third or fourth branches along the stems.  Rhizophores axillary, ventral and dorsal, borne on lower-most part of the 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 first branches, then dimorphic throughout, coriaceous, upper surfaces dull to shiny green, slightly corrugate, lower surfaces shiny yellowish green to silvery green, striate, the outer bases short-to long-auricled (these tend to disappear on leaves above first branches), the auricle shortto long-ciliate, cilia 2-10, each 0.2-0.5 mm long. Lateral leaves on main stem after first branches distant to slightly imbricate, strongly ascending to slightly spreading, ovatedeltate to ovate-oblong, 2.0-4.2 × 0.9-2.2 mm; bases truncate, on main stem before first branches with an inner, acroscopic bases strongly overlapping stems, rounded, entire, basiscopic bases free from stems, geniculate, usually ciliate, cilia 1-5, each 0.1 to 0.2 mm long; acroscopic margins on main stem leaves after second branches greenish to narrowly hyaline along proximal ⅔, 1-3 cells wide with the cells elongate, sinuatewalled and glabrous, parallel to margins, otherwise greenish, on branch leaves narrowly hyaline along proximal ¾ and cells as those on main stem, otherwise greenish distally, long-ciliate along proximal ½-¾, otherwise becoming short-ciliate to dentate distally, basiscopic margins greenish, comprising similar cells as in acroscopic margins, entire along proximal ⅔, otherwise sparsely denticulate distally; apices gradually tapering, acute to broadly acute, tipped by 1-3 teeth; upper surfaces comprising irregularly shaped, somewhat rectangular to quadrangular, sinuate-walled cells (often difficult to distinguish because of waxy deposits), with some obscure, idioblast-like, short quadrangular to round or elongate and variously papillate cells, without stomata or with some obscure along basiscopic margins, lower surfaces comprising elongate, sinuatewalled cells, with many of these idioblast-like, elongate and papillate, papillae 5-14 in 1 or 2 rows on each cell lumen, stomata on 1-5 rows along midribs. Median leaves on main stems after first branches distant to slightly imbricate, ascending, ovate, broadly ovate to ovate-elliptic, 1.4-3.0 × 0.8-1.7 mm; bases truncate to truncate-oblique, the outer base tufted with (4)6-20 long hairs, without auricles; margins greenish to narrowly hyaline, 1 or 2 cells wide with the cells elongate, slightly sinuate-walled and mostly glabrous or papillate, parallel to margins, the inner margins short-ciliate along proximal ⅔, denticulate along distal ⅓, the outer margins entire along proximal ⅓, becoming short-ciliate along medial ⅓, otherwise denticulate on distal ⅓; apices acute to slightly acuminate, the acumen ca. 0.1 mm, tipped by 1-3 teeth; upper surfaces comprising irregular (jigsaw puzzle-like), sinuate-walled cells (often difficult to distinguish because of waxy deposits), some of these papillate, papillae 3-14, irregularly arranged, without elongate idioblasts, stomata in 3-7 rows along the midribs and marginal to submarginal along basiscopic ⅓ of outer margins, lower surfaces comprising elongate (jigsaw puzzle-like), sinuate-walled cells, without elongate idioblasts and stomata. Axillary leaves on main stem after first branches ovate-lanceolate, 2.0-3.0 × 0.9-1.5 mm; bases rounded to cordate or truncate, with two small, long-ciliate auricles up to, at least, the fifth branch and then becoming small lobes; margins narrowly hyaline as in median leaves, long-ciliate along proximal ⅘, otherwise short-ciliate to denticulate distally; apices gradually tapering, acute, tipped by 1-3 teeth; both surfaces as lateral leaves. Strobili terminal on main stem and each branch tip, quadrangular, 0.3-1.7 cm. Sporophylls monomorphic, without a laminar flap, each with a slightly developed and seemingly glabrous keel along midribs, ovate to ovate-lanceolate, 0.8-1.0 × 0.4-0.6 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, short-ciliate along proximal ½, otherwise denticulate to entire distally; apices acute to acuminate, the acumen 0.1 to 0.2 mm, tipped by 3 tooth-like projections; dorsal sporophylls with upper and lower surfaces as in vegetative leaves; ventral sporophylls with both surfaces, silvery green to hyaline, comprising elongate, papillate, sinuate-walled cells. Megasporangia in 2 ventral rows; megaspores white, rugulate-reticulate on proximal faces with a slightly developed equatorial flange and microstructure granulate, perforate and sparsely echinate, mostly open to somewhat closely reticulate on distal faces with the microstructure sparse and minutely echinate and perforate, 180-250 µm diam. Microsporangia in 2 dorsal rows; microspores orange, echinate-rugulate on proximal faces with punctate microstructure, capitate or baculate on distal faces with each caput or bacula and the rest of the surface with echinate microstructure, 20-30 µm diam.
Habitat, distribution and phenology. Selaginella altheae grows on lowland and montane rainforests at 140-450 m; it is known from the Amazon basin of Colombia, Venezuela and Brazil and found fertile from April through to November.
Eponomy. I am delighted to dedicate this graceful, fern-like species with shiny idioblasts on leaf surfaces to my mother, Althea Quintero (1939-), whose gentle, selfless demeanor, as well as strength and enlightening life-long support has guided and buttressed my life and professional career. She has adorned my path in life in the same manner as her lovely and resilient namesake flower does in nature.
Conservation status. This is a widely distributed species that grows at low elevations in Tropical rainforests of the Amazon basin; therefore, it is considered here of Least Concern (LC), according to IUCN (2012)   Discussion. Selaginella altheae is characterized by its erect, fern-like habit, axillary, lateral and dorsal rhizophores, leaves on main stems becoming obviously dimorphic above or 1-4 cm below the first branches and, below this point, the lateral leaf bases oblique with an acroscopic auricle that is tufted with 3-15 stiff hairs and median leaves above first branches in main stems with oblique, not auricled bases, with the outer bases slightly prominent and tufted with (4)6-20stiff hairs.
Selaginella altheae, S. lechleri and other members of the S. flabellata group, have microspores distal faces with echinate microstructure. Likewise, S. altheae and S. oaxacana Spring have dorsal rhizophores, as do other members of the S. flabellata group. These two characters, therefore, might represent synapomorphies that define the S. flabellata group. Nevertheless, dorsal rhizophores, which are typical of articulate Selaginella species, are also found in other taxa such as S. psittacorhyncha (Valdespino 2017) and S. philipsonii, suggesting that this character is under-reported and, perhaps, of a wider presence in the genus than hitherto acknowledged. Similarly, different degrees of spore echinate microstructure could occur in other unrelated taxa. Therefore, the occurrence of these characters in morphologically unrelated species warrants further morphological, anatomical and molecular studies throughout the genus to ascertain their evolutionary and phylogenetic implications. Interestingly, a specimen of S. altheae (i.e. Thomas & Samuels 3291, NY) has flagelliform tertiary branch apices that develop strobilus at their tips.
Selaginella altheae is morphologically close to S. flabellata and S. lechleri. Their leaves on the main stems below the first branches are seemingly monomorphic and have similar median leaf above the first branches with the outer bases slightly prominent and tufted with either few or many short-to long cilia, as well as submarginal to marginal stomata along the proximal ⅓ on each outer half of the laminae. Nevertheless, S. altheae is set aside from S. flabellata by its median leaves on main stems ovate, broadly ovate to ovate-elliptic (vs. broadly ovate to ovate-oblong) with the inner and outer halves on the main stems equal in width or the inner halves slightly wider than the outer halves (vs. usually the outer halves distinctly wider) and lateral leaves acroscopic margins long-ciliate along proximal ½-¾ (vs. ¼-½), otherwise distally short-ciliate to dentate (vs. entire or denticulate). It differs further from S. flabellata by its megaspores proximal faces rugulate-reticulate (vs. rugulate) with granulate, perforate and sparsely echinate and perforate (vs. tuberculate, mostly psilate to minutely echinate and perfo-   Selaginella altheae may also be confused with the Central and South American S. anceps (C. Presl) C. Presl because of their auriculate leaf bases (i.e. auriculae present on lateral leaves of S. altheae and on seemingly monomorphic leaves of S. anceps) on main stems below the first branches. Selaginella altheae is set aside from the latter by its obviously dimorphic leaves immediately above or 1-4 cm below the first (vs. above fourth) branches of the main stems and median leaf bases on main stems above the first branches without auricles (vs. with inner and outer ciliate auricles or only with an outer ciliate auricle). It is further distinguished from S. anceps by its megaspores proximal faces with a slightly developed (vs. lacking) equatorial flange, rugulate-reticulate (vs. reticulate) ornamentation with granulate, perforate and sparsely echinate (vs. with perforate and strongly echinate) microstructures, while the distal faces ornamentation is mostly open or somewhat (vs. mostly) closely reticulate with sparse and minutely echinate and perforate (vs. shortly echinate, granulose and perforate) microstructures.
Selaginella squamulosa Valdespino, sp. nov. urn:lsid:ipni.org:names:77173691-1 Figures 6-10 Diagnosis. Selaginella squamulosa is set aside from similar S. psittacorhyncha and S. vernicosa by its median leaves upper surfaces with 10 (vs. with 25 in S. psittacorhyncha and 35 in S. vernicosa) stomata along the midribs. It differs further from S. psittacorhyncha by its lateral leaf acute (vs. obtuse) apices and hyaline (vs. greenish) margins and median leaf bases oblique (vs. truncate) and from S. vernicosa by the median leaf upper surfaces made up of quadrangular and rectangular (vs. undistinguishable, somewhat appearing quadrangular or elongate) papillate cells and lateral leaf margins on acroscopic side serrate to denticulate (vs. short-ciliate, at least along proximal ⅔) and on basiscopic side sparingly denticulate or entire to slightly denticulate distally (vs. short-ciliate at least along proximal ⅓).
Description. Plants terrestrial, epiphytic or epipetric. Stems creeping, stramineous, 10-20 cm long, 0.4-0.8 mm diam., non-articulate, often flagelliform, not stoloniferous, 1-2(3)-branched. Rhizophores axillary along proximal ½ of stem, filiform, 0.1 to 0.2 mm diam. Leaves dimorphic, coriaceous. Lateral leaves distant to imbricate towards stem and branch apices, ascending, broadly deltate-ovate, broadly ovate or ovate-elliptic, (1.0)1.3-1.7 × 0.8-1.7 mm; bases rounded, acroscopic bases overlapping the stem, basiscopic bases free from the stem; margins hyaline, made up of a band 2-4 cells wide, the cells elongate and papillate, parallel to margin, papillae in a single row over cell lumen, acroscopic margins serrate to denticulate, basiscopic margins sparingly denticulate or entire to slightly denticulate distally; apices broadly acute to acute, tipped by 2-4 teeth; both surfaces without idioblasts, upper surfaces mostly glabrous but with short hairs on submarginal  and marginal sections of basiscopic half of the lamina, made up of quadrangular to rectangular, irregularly-walled, papillate or not cells, papillae 5-10 over cell lumen arranged in 2 or 3 rows, midribs not prominent, without stomata, lower surfaces glabrous, made up of elongate or asymmetric, straight or slightly sinuate-walled, papillate cells, papillae 8-20 over cell lumen arranged in 2 or 3 rows, midribs raised and prominent at mid-distal section of lamina, stomata concentrated on raised portion of midribs. Median leaves distant to imbricate towards stem and branch tips, ascending and, on branches, they may arise at ca. 45° angle, ovate to ovate-deltate, 1.0-1.5 × 0.6-1.0 mm; bases oblique, inner bases truncate to rounded, outer bases ventricose and often tufted with 2-8 very short hair or teeth; inner margins narrowly hyaline, made up of a band 1 or 2 cells wide, the cells elongate and papillate, parallel to margin, papillae in a single row over cell lumen, serrate to denticulate, outer margins greenish, denticulate at proximal ¼, otherwise sparingly denticulate or entire along middle and denticulate at distal ¼; apices acute, tipped by 2-4 teeth; both surfaces without idioblasts, upper surfaces mostly glabrous but occasionally with short hairs near marginal, submarginal and submedial section of outer half and on submedial section of inner half near distal ¼, made up of quadrangular or with some rectangular, irregularly-walled, papillate cells, papillae 5-10 over cell lumen arranged in 2 or 3 rows, midribs raised and prominent or bevelled specially at mid-distal section of each laminae, stomata concentrated on raised portion of midribs and some marginal on lower ½ of outer margins, lower surfaces glabrous, made up of elongate or asymmetric, straight or slightly sinuate-walled cells, midribs not prominent. Axillary leaves similar to lateral leaves. Strobili terminal and single on branch tips, quadrangular, 0.5-5 mm long. Sporophylls monomorphic, without a laminar flap, ovate to ovate-elliptic, 0.9-1.3 × 0.5-1.3 mm, with a keel along midrib on upper surfaces; base rounded; margins greenish, minutely denticulate to entire; apices acute; both surfaces without conspicuous idioblasts, both surfaces glabrous; dorsal sporophylls with upper surfaces green, except for the half that overlaps the ventral sporophylls where it is hyaline, lower surfaces greenish-hyaline; ventral sporophylls with both surfaces greenish-hyaline. Megasporangia one or two at the base of ventral rows; megaspore yellow, rugulate-reticulate on proximal faces with fissurate microstructure, reticulate-granular on distal faces with granulose and perforate microstructure, 410-445 µm diam. Microsporangia in dorsal rows and distal ¾ of ventral rows; microspores deep orange, proximal and distal faces not studied and not measured.
Habitat, distribution and phenology. Selaginella squamulosa grows as a terrestrial, epiphytic or epipetric plant on open slopes to cliff base, in rills and wet depressions of swampy savannas or on scrub dominated forests at 1950-2743 m; it is known from the Guiana Highlands in Cerro de la Neblina, Amazonas State of Venezuela and in Río Cuaburí, Amazonas State of Brazil and found fertile from October through to February.
Etymology. The specific epithet derives from the Latin "squamulosus", meaning minutely scaly and refers to the tiny, stiff leaves that resemble small scales.
Conservation status. Selaginella squamulosa is known from two distinct localities at high elevation in isolated tepuis in the Amazon basin of Venezuela and Brazil where Discussion. Selaginella squamulosa is distinguished by its centipede-like habit with slender and creeping stems, rhizophores restricted to the lower halves of the stems or often present on flagelliform stems and branches (i.e. Steyermark 103872, NY), coriaceous, scaly-like leaves with raised and prominent midribs on the lower and upper surfaces of the lateral and median leaves, respectively and acute leaf apices. In addition, the midribs on the upper surfaces of the median leaf are straight to strongly arcuate. In the latter case, the inner half of each leaf lamina becomes slightly wider than the outer one. It is further strikingly distinct by having the lateral leaf acroscopic halves on lower surfaces twice as wide as the basiscopic ones. Furthermore, as noted in other Selaginella species, on a duplicate specimen of S. squamulosa (i.e. Steyermark 103872, MO), a rhizophore becomes a leaf-bearing shoot. Remarkably, Boom et al. 6011 (NY, PMA, UC) has a more slender habit with the upper leaf surfaces hispidulous. Apparently, these hairs become caducous since they were not observed in a similar collection (i.e. Beitel 85161, NY, PMA) or in the more coriaceous form represented by the type.
The holotype and an isotype of Selaginella squamulosa at NY and MO, respectively, were originally identified as S. cruegeri Jenman vel aff., which is a synonym of S. minima Spring. The latter species differs most noticeably from S. squamulosa by its ascending (vs. creeping) habit, chartaceous (vs. coriaceous) leaves, median leaf with broadly hyaline margins (vs. inner margins narrowly hyaline and outer margins greenish) and white (vs. yellow) megaspores. A paratype of S. squamulosa (i.e. Boom et al.,6011,NY,PMA,UC) was determined as S. rhodostachya Baker vel aff. Nevertheless, S. squamulosa is easily set aside from S. rhodostachya by its coriaceous (vs. chartaceous) leaves, oblique (vs. rounded to truncate) median leaf bases with the outer bases ventricose (vs. rounded) and ovate (vs. ovate-elliptic) lateral leaf with its acroscopic margins, as well as both margins of the median leaf serrate to denticulate (vs. often long-ciliate). Another of the paratypes of S. squamulosa (i.e. Maguire et al. 60466,NY) was determined as S. brachyclada Baker. However, it differs from the latter by having the inner and outer margins of the median leaf narrowly hyaline and greenish, respectively (vs. both margins widely hyaline) and serrate to denticulate (vs. faintly denticulate), oblique (vs. truncate) bases, ovate or ovate-elliptic (vs. ovate-cordate) lateral leaf, which is distinctly wider at the middle (vs. at the base), ascending (vs. spreading) and deep yellow (vs. white to light-yellow) megaspores that lack (vs. have) a distinct equatorial flange. Selaginella squamulosa is part of the "Selaginella vernicosa group" and, amongst these, it is morphologically close to S. psittacorhyncha and S. vernicosa. It differs from these two species by the characters discussed under the diagnosis and by its median leaf with the midribs raised at the distal ½ of the laminae but not properly extending into the apices (vs. extending into the apices) with the upper surfaces occasionally puberulent (vs. glabrous). Selaginella squamulosa differs from S. arrecta by its median and lateral leaf apices broadly acute to acute (vs. long-acuminate to aristate), median leaf inner margins narrowly (vs. widely) hyaline, which consists of 1 or 2 (vs. 3-5) elongate cells wide and ca. 10 stomata on raised midribs (vs. up to 85 stomata, widespread on central portion of lamina). In addition, in S. squamulosa, 2-4 teeth tip the acute apices, whereas the acuminate or aristate apices of S. arrecta are made of 6-10, narrowly elongate and papillate cells. Selaginella squamulosa differs from S. roraimensis, S. marahuacae and S. scalariformis by its narrowly ovate-deltate or ovate (vs. ovate-oblong or oblong in S. roraimensis and ovate-elliptic in S. marahuacae and S. scalariformis) lateral leaves with midribs on lower surfaces distinctly raised (vs. plane in profile). Selaginella squamulosa is further separated from S. roraimensis by the lateral leaf basiscopic margins extended (vs. slightly reflexed), from S. marahuacae by its acute (vs. shortly acuminate) median leaf apices and from S. scalariformis by its distant to imbricate and ascending (vs. distant and patent) lateral leaves. Description. Plants terrestrial or epipetric. Stems creeping, stramineous, 6-10 cm long, 0.2 to 0.3 mm diam., non-articulate, not flagelliform, not stoloniferous, 1-branched.
Leaves dimorphic, chartaceous. Lateral leaves imbricate, ascending to spreading, ovate, ovate-elliptic or ovate-oblong, (1.0)1.2-1.7 × 0.6-1.2 mm; bases rounded, acroscopic bases overlapping the stem, basiscopic bases free from the stem; acroscopic margins on upper surfaces greenish to greenish hyaline, made up of a band 1 or 2 cells wide, the cells elongate and papillate, parallel to margins, the papillae in one or two rows over each cell lumen, on lower surfaces hyaline, made up of a band 3-5 cells wide, the cells elongate and papillate, parallel to margin, the papillae in one or two rows over each cell lumen, long-ciliate throughout, the hairs long on proximal ¾ and distally smaller, basiscopic margins on upper and lower surfaces greenish, made up of a band 1 or 2 cells wide, the cells elongate and glabrous, parallel to margins, sparsely short-ciliate throughout or seemingly denticulate along proximal ¾ and with short hairs along distal ⅓ and with marginal stomata along proximal ½; apices obtuse to broadly acute or acute, tipped by (1) 2 (4), often divergent, long cilia; upper surfaces with elongate, idioblast-like cells at the base, the idioblasts papillate, the papillae in two rows, otherwise idioblast absent, most of the surface made up of irregular, quadrangular to rectangular, irregularly-walled, papillate cells, the papillae 9-15 irregularly arranged over each cell lumen or some cells glabrous, especially toward basiscopic bases, the laminae pubescent near basiscopic margins, the midrib not prominent, without stomata, the lower surfaces glabrous, made up of elongate, straight-walled, idioblast-like and papillate cells, the papillae 10-30 over each cell lumen, arranged in 2 or 3 rows and often interconnected, midrib not raised or prominent, with stomata in 2 or 3 rows concentrated along raised portion of midrib. Median leaves imbricate, ascending, narrowly lanceolate to narrowly lanceolate-elliptic, 0.5-1.2 × 0.3-0.6 mm; bases oblique to obtuse, glabrous; the inner margins broadly hyaline, made up of a band 2-7 cells wide, the cells elongate, idioblast-like, papillate and parallel to margins, papillae in 1 or 2 rows over each cell lumen and some of these interconnected, proximally entire and short-ciliate along distal ⅔, the outer margins greenish, made up of 2 or 3 elongate and glabrous cells and with the submarginal portion of the lamina conspicuously hyaline, made up of a band of 8-12 cells wide, the cells elongate, idioblast-like, papillate and parallel to the margins, papillae in 1 or 2 rows over each cell lumen and some of these interconnected; apices acute, attenuate to shortly acuminate, tipped by 1-5 long, divergent cilia or more often by two long, divergent cilia, the acumen or arista 0.  'W, 250 m, 7 Nov 1979, Steyermark et al. 119488 (MO, UC).
Discussion. Selaginella philipsonii was originally described as a subspecies of S. ovifolia by Jermy and Rankin in Alston et al. (1981: 294). They indicated, however, that Alston considered it a new species, a conclusion with which the author fully concurs and hence its recognition here at that level. According to Alston (1955: 244), S. ovifolia is a taxon found in the Dominican Republic, Haiti, Jamaica, Puerto Rico and Belize. Certainly, these two taxa share a moss-like habit and median leaf apices ending in long cilia. Nevertheless, S. philipsonii is most distinguished by the median leaves on main stems imbricate, oblong-elliptic with the inner margins hyaline, made up of a band of 2-7, elongate and papillate cells and shortly ciliate and the outer margins greenish, made up of 2 or 3 elongate and glabrous cells and the submarginal portion of the laminae conspicuously hyaline, composed of a band of 8-12 cells wide, with the cells elongate and papillate, parallel to the margins, the papillae in 1 or 2 rows over each cell lumen and some of these interconnected (see Figs 11A-D, 16B in Alston et al. 1981: 296), entire and the apices acute, attenuate to shortly acuminate, tipped by 1-5 (Fig. 11C) or often 2 long, divergent cilia, the acumen or arista 0.1-0.3 mm long. It is further characterized by the lateral leaves acroscopic margins long-ciliate, the basiscopic margins denticulate, the apices obtuse to broadly acute or acute, tipped by (1) 2 (4), often divergent, long cilia ( Fig. 11E-G). In addition, SEM images of the median leaves show stomata along the outer margins, as well as on the midribs (Fig. 11B-D). Conversely, S. ovifolia is characterized by median leaves on main stems distant, elliptic to ovate-elliptic, the margins sparingly short-to long-ciliate, having the outer margins and the outer submarginal portion of the laminae greenish, composed of rounded cells or the outer margins only slightly hyaline on distal ¼ and made up of only 1 or 2 elongate and papillate cells, while the inner margins are greenish, comprised of roundish cells, the apices long-acuminate, tipped by 2 long cilia, the lateral leaf acroscopic margins long-ciliate, while the basiscopic margins are short-to long-ciliate and the apices acute or short-to long-acuminate, tipped by 1-3 teeth or short cilia.
Selaginella philipsonii is morphologically close and may be confused with S. homaliae A. Braun and S. schultesii Alston ex Crabbe & Jermy, which are both from South America, because of their moss-like habit, slender rhizophores, minute leaves and keeled sporophylls with the keel short-ciliate to dentate. Selaginella philipsonii differs noticeably from S. homaliae and S. schultesii by its median leaf outer margins greenish (vs. con-handiwork of the novel plant illustrator Rubén Lozano. I am indebted to my students Christian López and José Palacios for their assistance in various aspects of this study, as well as to Jorge Ceballos (STRI) for his help with the SEM work, Christopher Gioia for his continuous encouragement and proofreading of an early English draft of this paper and Pedro Argudo of NovoArt for help preparing plates. Finally, thanks are also due to Robbin Moran (NY), Alexandre Salino (BHCB) and another anonymous reviewer as well as the staff of PhytoKeys, including A. Troia, subject editor, for their suggestions to improve the manuscript.