Eleocharis yecorensis (Cyperaceae), a new species of spike-sedge from México

Eleocharis (Cyperaceae) includes approximately 200 species and is particularly diverse in the New World. A newly discovered species of subgenus Limnochloa is described from the states of Sonora and Mexico, Mexico. Eleocharis yecorensis is related to E. acutangula, E. mutata. and E. quadrangulata and can be distinguished from these species by its five-angled culms, obdeltoid achenes. and narrow neck between tubercle and achene body. In addition. E. yecorensis possesses root storage structures similar to those found in the Chinese water chestnut, Eleocharis dulcis.

Eleocharis R. Br. (Cyperaceae), the spike-sedges, includes about 200 species and has a world-wide distribution (Gonzalez-Elizondo and Peterson 1997). New World diversity is impressive, and more than 45 taxa are recognized in Mexico alone (Espejo-Serna and L6pez-Ferrari 1997). While supraspecific taxonomy in this genus is problematic (Kukkonen 1990), one commonly recognized group is Eleocharis subgenus Limnochloa, to which the new species here described belongs.
Phenology.-Fruiting probably from September to November.
Distribution and habitat.-The states of Sonora and Mexico in Mexico. The type locality in a high elevation basin submerged in the wet season, with heavy silt-clay soil which dries completely during the dry c.

SUBG. LIMNOCHWA
Based on culm characteristics, Limnochloa can be divided, in very general terms, into the groups: the septate members with nonangled culms; the nonseptate members with angled, coarse culms [ ( 1) 2-8 mm diam); and the nonseptate members with angled, slender culms (0.7-2 (3.4) mm diam]. The only member of Limnochloa that does not fit well into one of these groups is E. cellulosa Torr. This species is nonseptate, but is also not angled, and while there is little question that it is part of Limnochloa, how it is related to the other members is unknown.
Eleocharis yecorensis belongs to the nonseptate, angled coarse-culmed species group which includes E. quadrangulata (Michx.) Roem. & Schult., E. mutata (L.) Roem. & Schult., E. spiralis (Rottb.) Roem. & Schult., and E. acutangula (Roxb.) Schult. Fernald (1925) provided characters for distinguishing New World E. mutata, E. quadrangulata, and E. acutangula (as E. fistulosa (Poir.) Link). These included achene size, achene shape, tubercle shape, and the width of the neck connecting the tubercle and achene apex. Ranges in achene size for each of these species are as follows: E. quadrangulata, 2. 7-4.2 mm; E. mutata, 1.7-2.3 mm; and E. acutangula, 2.0-2.8 mm. While the ranges in achene size of all of these species overlap, when used in combination with other characters, the species are relatively easy to differentiate. There are distinct, though subtle, differences in achene shape and size of the neck between tubercle and achene body among these species. The overall shape of E. yecorensis achenes seems most similar to E. acutangula in having achenes broadly obovate in outline. Both E. quadrangulata and E. mutata have obovate achenes tending towards a more elliptical shape. The neck between tubercle and achene body is narrow in E. ye-corensis, usually 1 A to ¥.! the width of the achene, which is similar to E. quadrangulata, while in E. acutangula the neck is usually about 112 the width of the achene body and in E. mutata it is lacking. The most obvious character for distinguishing most of these species is culm angulature. Both E. mutata and E. acutangula are three-angled, E. quadrangulata is four-angled, and E. yecorensis is five-angled. This character appears to be consistent both within and among populations of each species.
Recently, species status of E. mutata has been called into question in a report by Browning et al. (1997)that E. mutata is a hybrid between E. dulcis and E. acutangula. This is questionable for several reasons. First, E. mutata was originally described from the New World (Linnaeus 1759), only more recently being reported as occurring in Africa (Hooper 1972;Haines and Lye 1983;Browning et al. 1995). Eleocharis dulcis, on the other hand, is not native to the Americas. It has been cultivated in the U.S., but there are no reports of its escape, and E. mutata has been known from the Americas far longer than E. dulcis has been cultivated here. This brings into question what is being called E. mutata in Africa. It may be that a hybrid in Africa looks superficially like E. mutata. Detailed population studies of these species across their ranges are necessary to explain this confusion. Also, the culm transverse anatomy of E. mutata and E. acutangula is distinctly different from E. dulcis, and hybrids (at least F 1 s) would be expected to be variable for culm anatomy. That is not what is seen, at least for E. mutata in the New World. The primary rational that Browning et al. (1997) give for the hybrid status of E. mutata is its "approximate intermediacy" between E. acutangula and E. dulcis and they provide a table of morphological characters and the states for each taxon (Browning et al. 1997, p. 178). When this table is examined critically, few if any of the characters are truly intermediate. Also, E. dulcis is a member of the septate Limnochloa species with nonangled culms. For these reasons, E. mutata is being treated here as a distinct species based on culm transverse anatomy, achene shape, scale shape and texture, culm angulature, septae presence, spikelet morphology, and geographic distribution. Eleocharis spiralis, on the other hand, which may be confused with E. mutata, is historically known from Madagascar (Svenson 1939), and shares most of its geographic range with E. dulcis and E. acutangula (Svenson 1939). The relationship among these species needs to be pursued.
In addition to the characters of angulature, culm coarseness, and the lack of culm septae, there are several culm anatomical characters which distinguish these four species from the rest of Limnochloa and all other species of Eleocharis, at least those whose culm transverse anatomy has been studied (Metcalfe 1971;Govindarajalu 1975;Ueno et al. 1989). The most obvious characters separating these species from the rest is the presence of the net system of parenchyma cells through the air-cavities and the distribution of vascular bundles throughout the culm, not just along the periphery. Although several species of Eleocharis are known to have a net system through the central cavity (Govindarajalu 1975;Ueno et al. 1989), no species outside of the four species discussed here has been shown to have vascular bundles along this net. Also, the shear number of vascular bundles (50-120) within the culm far exceeds that found elsewhere in the genus (Metcalfe 1971;Govindarajalu 1975;Ueno et al. 1989).
Eleocharis yecorensis is the first New World member of Limnochloa observed to have root storage structures. These swollen structures have an expanded cortex region which turns deep black when stained with iodine/potassium iodine indicating starch storage. Eleocharis dulcis, also of Limnochloa, is well known for its root storage structures.
Eleocharis yecorensis, E. quadrangulata, E. mutata, and E. acutangula occur in similar habitats. These can vary from freshwater ponds and lakes to brackish coastal waters (Svenson 1957). Eleocharis quadrangulata, E. mutata, and E. acutangula seem to only inhabit those wetland areas that have consistent water levels and are submerged year-round. Eleocharis yecorensis, at least at the type locality, dominates a wetland of deep standing water, but this basin completely dries up during the dry season and has been used for horse grazing (T. VanDevender pers. comm.). KEY