Taxonomic revision of Neotropical Murdannia Royle (Commelinaceae)

Abstract This study provides a taxonomic revision for the Neotropical species of the genus Murdannia. Six species are recognized as native, including a new species and a new combination, while two Asian species are recognized as invasive. We present an identification key, a table summarizing the morphologic differences among the species, a new synonym, six lectotypifications, a distribution map, and descriptions, comments and photographic plates for each species. We also provide comments on the morphology of the Neotropical species of Murdannia, comparing them with the Paleotropical species, and a discussion of inflorescence architecture in the genus as a whole.


Introduction
Murdannia Royle is one of the largest genera in Commelinaceae, comprising ca. 60 species (Faden 1998;eMonocot 2010; Th e Plant List 2013; Govaerts and Faden 2016). It was described by Royle (1840), based on Aneilema scapifl orum Roxb. [= M. edulis (Stokes) Faden], and was named after Murdan Ali, the keeper of the Saharanpur Botanic Garden herbarium at India. Unware of Royle's name, Brückner (1926) described Phaeneilema G.Brückn., and transferred several species from Aneilema to his new genus (Brückner 1926(Brückner , 1927. A few years later, in his treatment for Commelinaceae in Engler's Natürlichen Pfl anzenfamilien, Brückner (1930) realized that Phaeneilema and Murdannia were congeneric and made the required combinations. Pichon (1946) pointed out the existence of two names prior to Murdannia (i.e. Dilasia Raf. and Streptylis Raf.), both published by Rafi nesque (1838) in his Flora Telluriana. Since both names were published in the same work and none had priority over the other, Dilasia was adopted by Pichon (1946) as the accepted name. Nevertheless, Brenan (1952), noted that most of the necessary combinations in Murdannia had already been made by Brückner (1930). Th us, the author proposed to conserve Murdannia against Dilasia and Streptylis, to avoid the unnecessary creation of about 30 new combinations in the monospecifi c Dilasia (Brückner 1930;Merrill 1937).
Murdannia nom. cons. is currently placed in subfamily Commelinoideae, tribe Commelineae, together with Aneilema R.Br., Buforrestia C.B.Clarke, Commelina L., Floscopa Lour., Pollia Th unb., and Stanfi eldiella Brenan, among others (Faden and Hunt 1991;Evans et al. 2003;Burns et al. 2011;Faden 1998). As aforementioned, Murdannia species have been historically treated under Aneilema by several authors (e.g. Brown 1810; Clarke 1881; Bentham and Hooker 1883;Woodson 1942), and sometimes also under Commelina. Nevertheless, Murdannia can be easily diff erentiated from Aneilema and Commelina by its fl owers commonly enantiostylous, petals sessile and equal to subequal, three antesepalous stamens (one sometimes staminodial), three antepetalous staminodes, 3-lobed antherodes, capsules always equally 3-locular, and 3-valved (Brenan 1952(Brenan , 1966Faden 1998). Th e genus has a Pantropical and Warm Temperate distribution, being especially diverse in Asia, where most (more than 50%) of the accepted species and morphological diversity are known to occur (Nandikar 2013;Ancy 2014;Ancy and Nampy 2014;Nandikar and Gurav 2015). Most recent studies on Murdannia have focused on the Paleotropical species, especially the Asian (e.g . Faden 2001;Nandikar 2013;Ancy 2014;Ancy and Nampy 2014;Nandikar and Gurav 2015) and the African (Faden 2012) members of the genus. Nevertheless, very little is known about the Neotropical species of the genus (Pellegrini et al. 2013). A total of four Neotropical species of Murdannia were accepted in the most recent account on the group (Barreto 1997;eMonocot 2010), with the occurrence of M. schomburgkiana (Kunth) G.Brückn. in Brazil being considered doubtful. Barreto (1997), in her unpublished Ph.D. thesis and based on the limited material she had available, also considered the M. gardneri (Seub.) G.Brückn. species complex to be composed of a sole and widely polymorphic and distributed species. In the most recent checklist for the Brazilian Flora (BFG 2015), Barreto's taxonomic viewpoints were followed in detail, with the sole addition of M. nudifl ora (L.) Brenan as an invasive species.
Recent fi eld and herbaria studies have shed some light in this neglected group. As a fi rst attempt to clarify the taxonomy and systematics of Neotropical Commelinaceae, the present study provides a revision of the Neotropical species of Murdannia, with the description of a new species (endemic to Central-Western Brazil), and a new combination. We also provide a detailed taxonomic treatment on the group and comments on the morphology and systematics of Murdannia as a whole. . Th e distribution of the species is based on herbarium materials, fi eld data and literature. Th e classifi cation of the vegetation patterns follows IBGE (2012). Th e indumenta and shapes terminology follows Radford et al. (1974); the infl orescence terminology and morphology follows Weberling (1965Weberling ( , 1989 and Panigo et al. (2011); the fruit terminology follows Spjut (1994) and Ancy and Nampy (2014); and seeds terminology follows Faden (1991) and Ancy and Nampy (2014). Th e conservation statuses were proposed following the recommendations of IUCN Red List Categories and Criteria, Version 3.1 (IUCN 2001). GeoCAT (Bachman et al., 2011) was used for calculating the Extent of Occurrence (EOO) and the Area of Occurrence (AOO). Th e generic description of Murdannia presented in this work applies only to the Neotropical region, and is not meant to refl ect the entire morphological diversity of this widespread and diverse genus.

Results
In the present work, we accept six species native to the Neotropical region, with a new combination and a new species, and recognize two invasive Asian species. We present below descriptions for all native species, detailed diagnosis for the two invasive species, and a table summarizing the morphologic diff erences between all species found in the Neotropical region (Table 1). We also provide comments on the morphology of the Neotropical species of Murdannia, comparing them with the Paleotropical species, and a discussion of infl orescence architecture in the genus as a whole. Description. Herbs, perennial or annual, rhizomatous or not, with a defi nite or indefi nite base, terrestrial to paludal to rooted emergent aquatics. Roots thin and fibrous or tuberous and fusiform. Rhizomes short to elongate. Stems trailing and ascending at the apex or erect, unbranched to densely branched, rooting in the rhizome and at the basal nodes, rarely at the distal ones when they touch the substrate. Leaves sessile; distichously or spirally-alternate, congested at the apex of the stem or evenly distributed along the stem; lamina fl at to slightly falcate to falcate and/or conduplicate, base symmetrical, midvein inconspicuous to conspicuous, adaxially impressed or not, abaxially prominent or not, secondary veins conspicuous to inconspicuous. Synfl orescence composed of a solitary main fl orescence or with 1-several cofl orescences. Main fl orescences (infl orescences) terminal or axillary in the in the uppermost nodes, not perforating the leaf-sheaths; main fl orescence a thyrse, composed of 1-many cincinni; basal bract reduced to leaf-like; peduncle bracts (sterile bracts) absent; cincinni bracts persistent; cincinni, sessile to pedunculate, contracted to elongate, bracteoles fl at or tubular, persistent or caducous. Flowers bisexual or male (the male ones with a reduced gynoecium), actinomorphic, zygomorphic or enantiostylous, chasmogamous, fl at (not tubular); pedicels erect at anthesis and pre-anthesis, erect or defl exed at post-anthesis; sepals 3, equal, free, cucullate, membranous to chartaceous, dorsally not keeled, margins hyaline, accrescent and persistent in fruit; petals 3, sessile, equal to subequal, free, deliquescent, glabrous or with minute glandular hairs at base or medially bearded with moniliform hairs on the adaxial surface; stamens (2-)3, equal, antesepalous, fi laments bent ca. 30° either to the left or to the right, free, glabrous or with minute glandular hairs or medially bearded with moniliform hairs, anthers dorsifi xed, rimose, connective narrow, anther sacs parallel, elongate; staminodes 3-(4), antepetalous (if 4 staminodes are present, than 1 antesepalous to the lower sepal), fi laments free, glabrous, minutely glandular-puberulous basally or medially bearded with moniliform hairs, antherodes dorsifi xed, 3-lobed, indehiscent, connective expanded, golden yellow or mauve to purple; ovary sessile, bent ca. 30° on the opposite direction as the stamens, smooth, glabrous or glandular-puberulous, 3-locular, locules equal, locule 1-2-(6)-ovulate, style erect or gently curved at the apex, stigma truncate to capitate, papillate. Capsules loculicidal, 3-valved, apiculate due to persistent style base, smooth, glabrous or glandular-puberulous. Seeds exarillate, farinose, uniseriate, 1-2-(6) per locule, reniform to broadly ellipsoid or cuboid to polygonal, slightly to strongly cleft towards the embryotega, ventrally fl attened or not, testa costate to slightly rugose or shallowly scrobiculate to scrobiculate to foveolate, with ridges radiating from the embryotega, appendaged or not, hilum elliptic or linear, embryotega lateral to semilateral or semidorsal.
Ecology and habitat. As with most aquatic plants, Neotropical Murdannia are seldom collected throughout their distribution range. Despite that, they seem to be locally common or uncommon, depending on the species. Th ey all seem to be intimately related to permanent and seasonal water bodies of drier domains and vegetation, such as fl ooded grasslands in the Cerrado, Chaco and Pantanal domains, or the white sand formations in the Amazon basin.
Morphological relationships among the Neotropical species and within the genus. Murdannia is one of the six (i.e. Aneilema, Buforrestia, Commelina, Floscopa and Pollia) out of 41 genera of Commelinaceae distributed in the Neotropics and Paleotropics. (Faden 1998). Although few in number, the Neotropical species of Murdannia exhibit all the extremes in infl orescence morphology found in Murdannia as a whole. Th e terminal thyrse consisting of well-spaced whorls of cincinni, present in M. gardneri and M. paraguayensis, is elsewhere present only in the rare Central African M. allardii Infl orescence architecture in Murdannia. Brenan (1966) has shown a great diversity of infl orescence architecture in Murdannia, with variations in the position of the main fl orescence, total number of cincinni, number of nodes with cincinni, number of cincinni per node, and degree of development of each cincinnus. According to Panigo et al. (2011), the basic infl orescence pattern for Commelinaceae is a manybranched, pedunculate and terminal thyrse, with verticillate cincinni, each cincinnus multi-fl owered. Based on Brenan (1966) and Panigo et al. (2011), we could also infer that the plesiomorphic infl orescence architecture for Murdannia would correspond to the basic infl orescence pattern for Commelinaceae. Brenan (1966) indicates that most of the variation in infl orescence architecture could be derived from this basic type, as exemplifi ed by the Asian M. divergens, by only three changes. On the other hand, Panigo et al. (2011) states that additional changes would be necessary to express all the known variation in the infl orescence morphology for Murdannia, as: (1) the production of cofl orescences, in addition to the main fl orescence; (2) variation in the length of the peduncle and internodes of the main fl orescence; (3) variation in the number of cincinni per node; (4) variation in the arrangement of cincinni on each node of the main fl orescence; (5) variation in the length of the cincinnus peduncle; and (6) variation in the total fl ower number per cincinnus. Th ese changes can occur separately or in diff erent combinations. In the most extreme cases, the infl orescences are mainly axillary, each being fascicle-like, and composed of a few 1-fl owered cincinni.
If we were to consider this stepwise change a possible evolutionary sequence within Murdannia, then the South American species with the most plesiomorphic infl orescence type would be M. gardneri. By its reduced number of cincinni per node and change in their arrangement, the infl orescence of M. burchellii could be morphologically derived from M. gardneri. Murdannia paraguayensis, shares the numerous verticillate cincinni of M. gardneri, but each cincinnus is reduced to a single fl ower. Murdannia engelsii has terminal or terminal and axillary infl orescences, that are reduced to single cincinni, but the cincinnus is 2-several-fl owered. Th e most reduced infl orescences, and perhaps the ones that accumulated the greatest number of stepwise changes, can be observed in M. schomburgkiana and M. semifoliata, in which most infl orescences are fascicle-like, axillary in the distal leaves, and with all cincinni 1-fl owered. Species with similarly reduced infl orescences are numerous in Asia  (Faden 2012;Ancy 2014). Nonetheless, some of them show characters not present in any of the Neotropical species, such as annual habit, biseriate seeds and yellow to orange fl owers. Th us, in the absence of a well sampled molecular phylogeny it would be impossible to state whether the Neotropical species represent one or several distinct lineages in Murdannia. Description. Herbs ca. 14.0-55.0 cm tall., perennial, rhizomatous with a defi nite base, terrestrial to paludal to rooted emergent in fl ooded fi elds. Roots thin, fi brous, brown to dark-brown, densely to sparsely pilose with medium to dark brown hairs, emerging from the rhizome and from the basal most nodes. Rhizomes short, light to medium brown, buried in the sand or ground. Stems trailing with ascending apex, thin, densely branched or branched only at the base; internodes 1.8-8.4 cm long, green to vinaceous to reddish brown, sparsely pilose to hispid with hyaline hairs, becoming glabrous with age, with a line of eglandular hyaline hairs opposite the leaf above. Leaves spirallyalternate, evenly distributed along the stems, the distal ones gradually smaller than the proximal ones; sheaths 0.3-1.3 cm long, vinaceous to reddish brown, sparsely pilose to hispid with hyaline hairs, becoming glabrous with age, hairs hyaline, margins setose, with a line of eglandular hairs opposite to the leaf above; lamina 2.7-13 × 0.3-0.6 cm, linear to linear oblong, membranous, conduplicate, slightly falcate, light green to greyish green on both sides, drying light brown to olive-green on both sides, sparsely pilose to hispid, becoming glabrous with age, rarely glabrous, base truncate, margins green, ciliate to setose throughout or only at base, apex acuminate to mucronate; midvein conspicuous, impressed adaxially, prominently acute abaxially, secondary veins 2-(3) pairs, adaxially inconspicuous to slightly conspicuous, dark green, abaxially somewhat conspicuous, dark green. Infl orescences 1-2-(4) thyrsi, terminal or axillary in the uppermost nodes, thyrse with (1-)2-16, alternate to subopposite cincinni; peduncles 2.3-7.6 cm, with a sparse mixture of eglandular (scabrid) and glandular, hyaline hairs; basal bract reduced or leaf-like, 1.4-5.1 × 0.1-0.3 cm, lanceolate to linear, sparsely pilose to hispid, rarely glabrous, base truncate, margins ciliate to setose, apex acuminate, veins inconspicuous, concolorous or green; cincinni bracts ca. 0.2-1.1 × 0.1-0.4 cm, triangular to broadly triangular, cup-shaped, light green to lilac, glabrous to pilose at base, base amplexicaul, non-perfoliate, margins glabrous to sparsely ciliate, apex caudate; cincinni 2-9-fl owered, erect, sinuate, cincinnus peduncle 0.4-2.2 cm, green to vinaceous to purple, with a mixture of sparse eglandular (scabrid) and sparse or more numerous glandular, hyaline hairs, cincinnus internodes 0.2-1.1 cm long, green to vinaceous to purple, with a mixture of sparse eglandular (scabrid) and sparse or more numerous glandular, hyaline hairs; bracteoles ca. 1.8-3.7 × 0.9-1 mm, persistent, triangular to broadly triangular, cup-shaped, light green to lilac, glabrous to sparsely pilose, base amplexicaul, non-perfoliate, margins glabrous or rarely sparsely ciliate, apex acuminate. Flowers bisexual or male, enantiostylous, ca. 0.5-1.2 cm diameter; fl oral buds narrowly ovoid to ovoid, 2.1-4 × 1-2 mm, green to lilac; pedicels 0.3-1 cm long, green to vinaceous to purple, with a mixture of sparse eglandular (scabrid) and sparse or more numerous glandular, hyaline hairs, erect and elongate in fruit; sepals 3.2-5 × 1.5-2 mm, triangular to ovate-triangular, cucullate, green, glandular to densely glandular, hyaline hairs, apex acuminate, margins hyaline light green to hyaline lilac; petals equal, 4-6.3 × 3-4.2 mm, obovate to narrowly obovate, slightly cucullate, pale lilac to lilac to pink, rarely white, glabrous, base cuneate, margins entire, apex obtuse to rounded; stamens 3, equal, fi laments glabrous, gently curved at the apex, 3.8-5.2 mm long, pale lilac to lilac or white, anthers narrowly elliptic to narrowly oblong, 0.8-1.0 × 0.3-0.7 mm, connective lilac, anthers sacs white, pollen white; staminodes 3, equal, fi laments glabrous, straight, 1.6-2.1 mm long, pale lilac to white, antherodes sagittate, 0.8-0.9 × 0.9-1.0 mm, connective golden yellow, lobes conspicuous, cream-colored to pale yellow; ovary ellipsoid to oblongoid, 0.9-1.8 × 0.6-0.8 mm, 3-locular, white to light green, smooth, glabrous, style gently curved at the apex, ca. 1.8-3.6 mm, pale lilac to lilac or white, stigma truncate, white to lilac. Capsules 2.8-4.4 × 3-4.8 mm, subglobose to globose, apiculate due to persistent style, 3-locular, 3-valved, light brown when mature, glabrous, smooth. Seeds 1 per locule, 1.9-2.8 × 1.3-2.1 mm, reniform to broadly ellipsoid, cleft towards the embryotega, ventrally fl attened, testa dark brown to greyish brown, densely farinose, costate to slightly rugose, with ridges radiating from the embryotega, with a tan appendage that extends ventri-laterally to the embryotega and basally into the hilum; embryotega semilateral, relatively inconspicuous, generally covered by a cream farina, without a prominent apicule; hilum linear, approximately the same length as the seed, in a deep depression. Distribution and habitat. Murdannia burchellii has a very fragmented distribution, probably due to lack of collections, being known to occur in Bolivia, Brazil (in the states of Goiás, Maranhão, Pará, Piauí and Tocantins), and Venezuela (Fig. 10). It grows in shady to open sandy river banks of the Amazon and Cerrado domains.

Key to the native and invasive species of Murdannia in the Neotropics
Phenology. It was found in bloom and fruit from October to July. Conservation status. Murdannia burchellii possesses a wide EOO (ca. 3,513,319.273 km 2 ), but due to the few and scattered collections known for this species, its AOO is considerably smaller (ca. 22,500.000 km 2 ). Th us, following the IUCN recommendations (IUCN 2001), M. burchellii should be considered Least Concern. Nonetheless, it is important to highlight the small number of collections and how fragmented the distribution of M. burchellii is. Also, the most recent collection was made in 1993. Which may indicate an ongoing decrease of size of the subpopulations and the loss of habitat for this species.
Nomenclatural notes. When describing Aneilema gardneri var. burchelli, Clarke (1881) lists two collections (W.J. Burchell 8165 and M.A. Weddell 2106). Since the name of Clarke's new variety honors W.J. Burchell, it seems logical to designate his collection as the lectotype. Aside from that, this collection is well distributed in several herbaria around the world. Furthermore, the specimen from K herbarium matches Clarke's description and has hand annotations made personally by Clarke. Th us, we designate this specimen as the lectotype for Aneilema gardneri var. burchelli.
When describing Aneilema gardneri var. glabrior, Clarke (1881) cites three collections by G. Gardner (2743, 3481, 4020). Th e specimen of at K Gardner 4020 is mounted on the same sheet as Gardner 3481, and both being annotated by Clarke as A. gardneri var. glabrior. Gardner 4020 is also the most well distributed of the three collections. Nonetheless, the specimen of at K represents M. gardneri, so it cannot be designated as the type of A. gardneri var. glabrior. Th us, the specimen at K is not considered part of the original material. One of us (RBF) examined and recorded a specimen of Gardner 4020 at BM in 1993, with the following data on the label: "Moist campos between Natividade and Conceição, Feby 1840, Herb. Gardner." While this would appear to be the most logical choice for a lectotype, the specimen was not photographed when other types were photographed at BM, and it cannot be found today. Th erefore, the specimen at P is here designated as the lectotype. Th is specimen also bears an identifi cation in Clarke's handwriting.
Discussion. Murdannia burchellii is morphologically similar to M. gardneri due to the general aspect of the plants, indumentum and by the presence of a ventri-lateral appendage in the seeds. It was traditionally treated as part of M. gardneri s.l. due to the number of cincinni per infl orescence, the posture of the pedicels at post-anthesis and in fruit, general fl oral and capsule morphology, and due to the hilum being positioned in a deep depression (Table 1). Nevertheless, both species can be readily diff erentiated by the stature and robustness of the plants, the insertion of the cincinni in the main axis of the infl orescence and testa ornamentation. Furthermore, the cincinni in M. burchellii are conspicuously sinuate, while the cincinni in M. gardneri are straight. After analyzing the syntypes for Aneilema gardneri var. glabrior, it became clear that they were conspecifi c with M. burchellii. All specimens possess the characteristic alternate to subopposite cincinni, being diff erentiated only from M. burchellii by sparser eglandular and glandular hairs in the infl orescence. All the analyzed specimens possessed some type of indumentum in the infl orescence, despite Clarke's description (1881) stating they were completely glabrous.
Some young specimens of Murdannia burchellii with infl orescences reduced to a solitary cincinnus, can be confused with specimens of M. engelsii. Nevertheless, these can be diff erentiated by their glabrous stems, leaf-blades with truncate base, sinuate cincinni, cup-shaped bracteoles, and glabrous androecium and gynoecium (vs. stems with glandular hairs, leaf-blades with an amplexicaul base, straight cincinni, fl at bracteoles and minutely glandular-pubescent androecium and gynoecium in M. engelsii) ( Table 1). Diagnosis. Similar to M. paraguayensis due to its defl exed pedicels at post-anthesis and when fruiting; petals with minute glandular hairs at base on the adaxial surface; fi laments, ovaries, styles and capsules with minute glandular hairs, and capitate stigma. It can be diff erentiated by its trailing stems, distichously-alternate leaves, infl orescence reduced to a solitary cincinnus, peduncles with a mixture of eglandular and glandular hairs, cincinni 2-7-fl owered, capsules broadly ovoid to broadly ellipsoid, and 1-seeded locules.
Specimens seen ( Etymology. Th e epithet honors the collector of the holotype, the Brazilian botanist Mathias Erich Engels, Orchidaceae taxonomist and dear friend of the authors. Distribution and habitat. Murdannia engelsii is endemic to Brazil, being known from the states of Tocantins, Mato Grosso and Mato Grosso do Sul (Fig. 10). It grows in shady to open sandy river banks of the Amazon, Cerrado and Pantanal domains. Its prostrate stems produce dense mats, generally near rocks and grasses.
Phenology. It was found in bloom and fruit from March to August. Conservation status. Murdannia engelsii possesses both a wide EOO (ca. 514,893.048 km 2 ) and a wide AOO (ca. 15,000.000 km 2 ). Following the IUCN recommendations (IUCN 2001), M. englesii should be considered Least Concern. Nevertheless, most of the known populations of M. engelsii are in areas currently being deforested and turned into pasture sites for cattle. We believe that this species is highly aff ected by human activity and should be considered Vulnerable [VU, A2cd+ B2ab(ii, iii,v)+D2].

Murdannia gardneri
It grows in open sandy river banks or fl ooded grass fi elds, of the Cerrado domain.
Phenology. It was found in bloom and fruit throughout the year. Conservation status. Murdannia gardneri possesses a EOO of ca. 497,658.992 km 2 and a AOO of ca. 20,000.000 km 2 . Most of the known collections are concentrated in central Brazil, where the native vegetation is commonly removed to give place to livestock. Th is is especially common in the Cerrado domain, due to its savanna vegetation being easier to remove than the dense rainforests of the Amazon and Atlantic Forest domains. Th us, we believe that M. gardneri should be considered Nearly Th reatened.
Nomenclatural notes. When describing Aneilema gardneri, Seubert (1855) lists two collections from G. Gardner (4020 and 4021). As aforementioned, Gardner 4020 consists of a mixture of M. burchellii and M. gardneri. Fortunately, the same is not true for Gardner 4021. Furthermore, the Gardner 4020 specimen at P was designated by us as the lectotype for A. gardnei var. glabrior. Th us, we designate a specimen at K as the lectotype for A. gardneri.
Discussion. Murdannia gardneri is morphologically similar to M. burchellii and M. paraguayensis due to their phyllotaxy and by the number of cincinni per infl orescence. It is morphologically more similar to M. burchellii due to the posture of the pedicels at post-anthesis and when fruiting, general fl oral and capsule morphology, and due to the hilum being positioned in a deep depression. Nevertheless, both species can be easily diff erentiated based on the insertion of the cincinni in the main axis of the infl orescence (alternate to subopposite in M. burchellii vs. verticillate in M. gardneri), the ornamentation of the testa (costate to slightly rugose vs. scrobiculate to foveolate), robustness of the plants (delicate vs. robust, branching pattern (densely branched at base vs. unbranched to little-branched), leaf-blade consistency (chartaceous vs. succulent), and some indumentum diff erences. On the other hand, M. paraguayensis can be readily diff erentiated from M. gardneri by its 1-fl owered cincinni (vs. many-fl owered in M. gardneri), defl exed pedicels post-anthesis and when fruiting (vs. erect), fi laments with minute glandular hairs (vs. glabrous), gynoecium and capsules with glandular hairs (vs. glabrous), capsule oblongoid to broadly oblongoid (vs. subglobose to globose), locules 2-seeded (vs. 1-seeded), and hilum in a shallow depression (vs. in a deep depression) (Table 1). Diagnosis. Herbs annual, with a defi nite base, terrestrial to paludal to rooted emergent in fl ooded fi elds. Roots thin, fi brous, brown, densely to sparsely pilose, emerging from the basal most nodes. Rhizomes absent. Stems prostrate, erect to ascending apex, unbranched or branched at the base, glabrous. Leaves distichously-alternate, distributed along the stems, rarely 1-2 congested at base, the distal ones gradually smaller than the basal ones;  Phenology. It was found in bloom and fruit throughout the year. Discussion. Murdannia nudifl ora can be easily recognized by its caduceus bracteoles, single terminal cincinni, two fertile stamens and four staminodes, and capsules with 2-seeded locules (Table 1). Description. Herbs ca. 20.0-150.0 cm tall, perennial, rhizomatous with a defi nite base, terrestrial to paludal to rooted emergent in fl ooded fi elds. Roots thin, rarely thick, fi brous, medium to dark brown, densely to sparsely pilose with medium to dark brown hairs, emerging from the short rhizome and from the basalmost nodes. Rhizomes short, light to medium brown, buried in the sand or ground. Stems prostrate, with erect to ascending apex, succulent, unbranched or only branched at the base; internodes 3.4-13.0 cm long, green to vinaceous, glabrous to sparsely pilose, becoming glabrous with age, with a line of eglandular hyaline hairs opposite the leaf above. Leaves spirallyalternate, sometimes becoming distichously-alternate at apex, evenly distributed along the stems, the distal ones gradually smaller than the basal ones; sheaths 1.2-3.3 cm long, green to vinaceous, glabrous to pilose along the fused edge, sometimes with a few scattered long, glandular hairs, margins ciliate to sparsely setose at base, hairs hyaline; lamina 2.5-23.6 × 0.4-1.2 cm, succulent, canaliculate, slightly falcate to falcate, green on both sides, drying light brown to olive-green or light green on both sides, linear-lanceolate to linear-elliptic or linear-oblong, glabrous, base truncate to rounded, margins light green to pink or vinaceous, ciliate to sparsely setose only at base, apex acute to acuminate; midvein conspicuous or inconspicuous, slightly impressed adaxially, slightly obtuse abaxially, secondary veins 2-3(-4) pairs, adaxially inconspicuous or slightly conspicuous, light green, abaxially slightly conspicuous. Infl orescences 1-(2), thyrsi, terminal or axillary from the uppermost node, thyrse with 9-24 verticillate cincinni, arranged in 3-9 whorls; peduncles 1.2-7.5 cm, with glandular to densely glandular, hyaline hairs; basal bract leaf-like, 2.1-3.2 × 0.9-1.2 cm, lanceolate, glabrous, base rounded, margins ciliate to setose only at base, apex acute to acuminate, veins inconspicuous or slightly conspicuous, concolorous to light green; cincinni bracts ca.
Th e specimen H.S. Irwin et al. 8425 looks very distinctive from the other analyzed specimens due to its: apparently creeping habit, leaves distichously-alternate at apex, sheaths with a few scattered long glandular hairs, blades with strongly undulate margins, short congested infl orescence, and very short pedicels. Nevertheless, it possesses the same infl orescence architecture, capsules with glandular hairs, and 2-seeded locules. We believe that the blades with strongly undulate margins may be a result of the drying process. Th us, we consider that these collections don't merit any taxonomic recognition. Murdannia schomburgkiana (Kunth) G.Brückn., Nat. Pfl anzenfam. (ed. 2) Description. Herbs ca. 30.0-65.0 cm tall, perennial, rhizomatous with a defi nite base, terrestrial to paludal to rooted emergent in open fl ooded savannas. Roots tuberous, thick and fusiform, medium to dark brown, densely to sparsely pilose with medium to dark brown hairs, emerging from the short rhizome and from the basal nodes. Rhizomes short, brown, buried in the sand or soil. Stems erect, succulent, unbranched; internodes 1.0-11.5 cm long, green to vinaceous, glabrous, sometimes with a line of hyaline eglandular hairs opposite the leaf above. Leaves spirally-alternate, evenly distributed along the stems, sessile, the distal ones gradually smaller than the basal ones; sheaths 0.  mm, triangular to ovate-triangular, cucullate, pink to pinkish brown, glabrous, apex acute, margins hyaline pink to hyaline vinaceous; petals equal, 0.8-1.3 × 0.8-1.0 cm, obovate to broadly obovate, slightly cucullate, lilac to purple, medially bearded with lilac to purple, moniliform hairs on the adaxial surface, base cuneate, margins entire, apex acute to obtuse; stamens 3, equal, fi laments gently curved at the apex, 4.4-5.2 mm long, lilac to purple, densely bearded with moniliform, lilac to purple hairs, hairs slightly shorter than the fi laments, anthers elliptic to oblong, 1.7-2.4 × 0.6-1.0 mm, connective brown, anthers sacs brownish lilac, pollen brownish lilac; staminodes 3, equal, fi laments straight, 4.1-5.0 mm long, pale lilac to lilac, densely bearded with moniliform, lilac to purple hairs, hairs slightly shorter than the fi laments, antherodes hastate, 0.9-1.7 × 1.3-1.7 mm, connective golden yellow, lobes conspicuous, creamcolored to pale yellow; ovary ellipsoid to oblongoid, 1.9-3.1 × 0.7-1.3 mm, 3-locular, light green to green, smooth, glabrous, style gently curved at the apex, ca. 4.1-5.4 mm, lilac to purple, stigma capitate, lilac to purple. Capsules 5.9-8.5 × 2.8-4.6 mm, 3-locular, 3-valved, oblongoid to broadly oblongoid, apiculate due to persistent style, light brown when mature, smooth, glabrous. Seeds (immature) 6 per locule, 2.7-3.3 × 2.6-3.1 mm, cuboid to polygonal, slightly cleft towards the embryotega, testa dark brown to greyish brown, densely farinose, scrobiculate, with ridges radiating from the embryotega; embryotega semilateral, relatively inconspicuous, without a prominent apicule, generally covered by a cream farina; hilum linear, ½ the length of the seed or smaller, on a weak ridge. Distribution and habitat. Murdannia schomburgkiana is known from only four collections from Guyana (including the type) and perhaps only one collection from Brazil (in the state of Amazonas) (Fig. 10). It grows in open fl ooded grass fi elds and savannas in the Amazon domain. Th e distance between the Rio Madeira specimen and the other specimens collected in Guyana, make clear how poorly collected this species is. It is widely possible that fi eld trips focusing on the group or in the white sand formations in the state of Amazonas will fi ll this distribution gap.

6.
It is interesting to highlight that both specimens from Brazil might represent different sheets of the same collection. Firstly, it is known that Dr. Alexandre Ferreira collected exclusively in Brazilian territory. Th us, despite the locality not being clearly stated in the label of the specimen at Kew, this is the only possible option. Secondly, the specimen at Paris was collected in Brazil, Provincia Rio Negro, at the margins of Rio Madeira (currently state of Amazonas). Th is was one of the most important areas collected by Ferreira, during his philosophical travels, and probably the longest part of this fi eldtrip. Also, it is widely known that many specimens collected by Friar Vellozo, Dr. Vellozo de Miranda and Dr. Alexandre Ferreira, were taken from Lisbon to Paris, during the Napoleonic Wars. Finally, the labels of both specimens possess comple-mentary information, where the locality in the label of the Paris' specimen is one of locations where Ferreira collected, and the date is congruent with this specifi c fi eldtrip. Moreover, the specimens on both sheets are very similar in appearance.
Phenology. It was found in bloom from June to October, and in fruit in October. Conservation status. Murdannia schomburgkiana is only known from fi ve (or at most six) collections, including the type species. Furthermore, the last known collections for this species are 11 years old, and the AOO of M. schomburgkiana is of only ca. 12.000 km 2 . Following the IUCN recommendations (IUCN 2001), M. schomburgkiana should be considered Endangered [EN, B1a+C2a(ii)+D1].
Nomenclatural notes. When describing Aneilema schomburgkiana, Kunth (1843) mentions "Rob. Schomburgk misit sub. no. 842". According to Stafl eu and Cowan (1985), Robert Schomburgk's collections are generally housed at BM or K. Despite having found two specimens at BM, the specimen at B (B100367820) possesses the annotation "Ex. herb. Kunth misit. 1841.", made in Kunth's handwriting and matching the protologue, and it is widely known that Kunth's herbarium was part of B (Stafl eu and Cowan 1979). Th us, it was the obvious choice for a lectotype. Th e two sheets at BM were observed and described in detail by one of us (RBF) in 1993. However, they were not photographed when other types at BM were photographed, and the specimens cannot currently be located. If found they should be treated as isolectotypes.
Discussion. Murdannia schomburgkiana can be easily confused with M. semifoliata (C.B.Clarke) G.Brückn., due to their tuberous roots, reduced infl orescences enclosed by the leaf-sheaths, cincinni bracts tubular, petals medially bearded with moniliform hairs on the adaxial surface, fi laments densely bearded with moniliform hairs, the number of seeds per locule of the capsule, and seed morphology. Th eir petals medially bearded with moniliform hairs on the adaxial surface, are quite unique within Murdannia. As aforementioned, this character is otherwise only known in Commelinaceae in M. simplex (in which the hairs are tiny and only present at the petal, being fundamentally diff erent), and in the distantly related genera Cochliostema Lem. and Geogenanthus Ule (Tribe Tradescantieae, subtribe Dichorisandrinae; Hardy and Faden 2004;Pellegrini in press). Nevertheless, the distribution of both species does not overlap and they grow in diff erent environments (white sand formations vs. fl ooded grass fi elds). Murdannia schomburgkiana can be diff erentiated by its 2.2-13.6 cm long blades of the leaves bearing infl orescences (vs. 0.2-1.8 cm long), leaf-blades margins glabrous (vs. ciliate), cincinni bracts 1.6-1.8 cm long (vs. 0.4-1.3 cm long), and brown anthers (vs. purple) (Table 1).
Despite the few collections known for this species, it is the authors' opinion that the morphological, geographical and environmental factors are enough to diff erentiate both species. Murdannia schomburgkiana and M. semifoliata are very similar to each other, and quite distinct from the remaining Neotropical species of the genus. Th ey are morphologically similar to some Asian and African species with fasciclelike, mainly axillary infl orescences, and 1-fl owered cincinni, such as M. axillaris and M. triquetra.  matched the protologue perfectly. Furthermore, it possesses a detailed description and was identifi ed by Clark himself. Th us, it is here designated as the lectotype of A. semifoliatum. Discussion. Murdannia semifoliata, as aforementioned, is morphologically similar to M. schomburgkiana. Th ey share a peculiar vegetative morphology, infl orescence architecture, and petals medially bearded with moniliform hairs on the adaxial surface, not similar to any other Neotropical species. Murdannia semifoliata is especially distinctive due to its extremely reduced blades of the leaves bearing infl orescences, produced during the fl owering period (Table 1). In most individuals, the blades are so reduced that the whole plant seems to be aphyllous. Furthermore, M. semifoliata and M. schomburgkiana are the only Neotropical species to possess more than two seeds per locule, which gives the seeds a peculiar cuboid to polygonal shape. Distribution and habitat. Known for certain only from this collection. Th e general habitat was recorded as "partially inundated forest remnant with slow stream and pools of standing water" and for this collection as "stems fl oating in pool of creek." A photograph of a plant from Colombia, which may or may not be the same species, was sent to the fi rst author, but without a corroborating specimen, so it has not been considered for this description. However, we have illustrated it in Fig. 9 to encourage collectors to look for it.
Th e M. keisak complex is widespread in Asia, ranging from India to China and Japan, growing in fl ooded grasslands and disturbed areas. In South America, it is known from only two collections, one from Venezuela and one from Colombia. Unfortunately, it seems that the specimen from Colombia went astray during shipping, since it was never received by the fi rst author.
Phenology. It was found in bloom and fruit in November. Conservation status. Following the IUCN recommendations (IUCN 2001), this species should be considered Data Defi cient. Correspondence by the second author with the collector Gerrit Davidse, indicated that this was not a disturbed habitat in which one would expect to fi nd introduced weeds. However, the habitat was under great pressure and possibly no longer exists.
Nomenclatural notes. Nandikar and Gurav (2015) designated the specimen at CAL (CAL0000025807) as the lectotype for A. triquetrum. Nevertheless, after analyzing the specimen, comparing it to the protologue and to the remaining specimens, it became clear that the specimen at CAL is not conspecifi c to the specimens at B, E and GDC. Ancy et al. (2015), unaware of the article published just few months earlier by Nandikar and Gurav (2015), designate the specimen at B (B100367814) as the lectotype for A. triquetrum. Th eir choice matches perfectly the protologue, and thus should be followed instead of the lectotypifi cation made by Nandikar and Gurav (2015). Nonetheless, if ever found, the specimen at K would make a much better choice of a lectotype. At the time of the description of A. triquetrum and the completion of his monograph (i.e. 1881), Clarke was working at K, and would had access to a possible specimen in the Wallich Herbarium, housed at Kew.
Discussion. Th is is a widely distributed species complex, being very common and well collected in Asia. Nevertheless, the morphologic limits between M. keisak and M. triquetra, as well as the application of these names, varies greatly according to each author. In Flora of China (Hong and DeFilipps 2000), both species are accepted, although somewhat tentatively, and are separated by the length of the sepals, shape and size of the capsule, and number and shape of the seeds. Th e authors also state that the morphologic diff erences seem to be associated with the geographic distribution of the taxa. Nevertheless, both descriptions overlap with the description presented by Faden (2000) for M. keisak, in North America. Ancy (2014), in her unpublished Ph.D. thesis, presents a thorough taxonomic account on Murdannia from India. Her description of M. triquetra matches very closely the two specimens known for South America, in sepal, petal and fruit morphology. Nonetheless, Ancy (2014) describes the fi laments as being glabrous, contrary to the bearded fi laments known for the South American specimens. Th e author also omits the description of the antherodes, which in the South American specimens are yellow and cordate. Nevertheless, some young fl ower buds dissected by the second author lacked hairs on the fi laments of the stamens and completely lacked staminodes, but that might have been a developmental stage and thus may not be a discrepancy. Th is could be related to the extremely immature state of the dissected buds, and could explain the discrepancy of our description and the description presented by Ancy (2014). Nandikar and Gurav (2015) published a second account on the Indian species of Murdannia. In their treatment, M. triquetra diff ers greatly from the South American specimens. However, it matches very closely the description presented by Hong and DeFilipps (2000), Faden (2000) and Chowdhury et al. (2015) for M. keisak. In these descriptions, the antherodes are described as sagittate and ranging from lilac to purple, and clearly do not match the South American specimens.
It is the authors opinion that a study focusing on the specifi c boundaries between these taxa is necessary. Nevertheless, since this species complex is only invasive in the New World, we also believe that the required investigation should be carried out in the plants native range. It is also possible that these Neotropical collections represent a distinct taxon, not closely related to the other native South American species. But a much better South American sampling for comparison and a much more detailed would be required. Field work, better sampling of herbaria specimens, detailed study of reproductive morphology, analysis of the protologues, and population studies might shed a light on the issue.

Conclusions
Neotropical Murdannia is represented by six native species confi ned to South America, mostly in Brazil. Th e species can be distinguished from one another by growth habit, branching pattern of the stems, phyllotaxy, indumentum type, infl orescence morphology, indumentum on the petals, androecium and gynoecium, capsule morphology, seed shape, and by the ornamentation of the testa. Two invasive species, native to Asia, are found in the Neotropics. Murdannia aff . triquetra is recorded for the fi rst time in South America. Despite being rarely collected, the known South American populations seem to be well-established and should be monitored to avoid the dispersal of yet another invasive species of Commelinaceae. It may be mentioned, for the sake of completeness, that the only other Murdannia species recorded from the Western Hemisphere is the Asian taxon M. spirata (L.) G.Brückn., which in naturalized in southern Florida, United States (Faden 2000).
Despite being seldom collected, Neotropical Murdannia are generally described in labels as forming large populations. It is possible that the lack of collections for the group is connected to: (1) the diffi culty to access the areas where they occur (e.g. Amazonian river banks); (2) general neglect of aquatic fl ora, due to logistic diffi culties in fi eld work; (3) the diffi culty to preserve Commelinaceae fl owers in dried specimens, discouraging botanists to collect them; (4) and lack of fi eld work focusing on herbaceous plants. Th e authors hope that the present work will encourage fi eld workers to collect Commelinaceae specimens in the Amazon, Cerrado, Chaco and Pantanal domains. Furthermore, the increase of collections will enable researchers to monitor these species' populations in order to update and provide more precise conservation assessments for them, and monitor the need for biological control of the known invasive species.
Although several studies focusing on morphology, anatomy and cytology of Murdannia are available in the literature, no comprehensive phylogenetic study has been presented up to date. Burns et al. (2011) were the fi rst to sample more than one species of Murdannia in a phylogenetic analysis. However, all of the fi ve sampled species were Asian and none represented the type-species. Th us, the monophyly of Murdannia is still to be tested in future studies. Ancy (2014) presented a morphological phylogeny, sampling exclusively the species native to India. In her analysis, the clades are supported by characters like infl orescence architecture, and androecium, capsule and seed morphology. As aforementioned, the Neotropical species of Murdannia are extremely peculiar in a considerable number of morphological characters, and nothing is known regarding their phylogenetic relationships, anatomy or even their cytology. Th us, three important questions about the Neotropical species are: (1) how are they related to one another; (2) what is the relationship between the Neotropical species and the rest of the genus; and (3) how many dispersal events the Neotropical lineages of Murdannia would represent. In a more general sense, it would also be important to understand the evolution of morphological characters in the genus on a phylogenetic framework, such as the infl orescence and androecium morphology.