Isoëtes texana

Isoëtes texana Singhurst, A.E. Rushing, & W.C. Holmes
(of Texas, the species being endemic to the state)

Local names: Tejas quillwort, Texas quillwort

Plant aquatic; leaves evergreen, green-yellow, 24–62 cm long, pliant, gradually thinning from base to pointed apex, laying flat on water surface; velum covering whole sporangium; megaspores white, 0.35– 0.40 mm, the surfaces not cobwebby, microscopically smooth to obscurely rugulose. The species is known only from “freshwater ponds and interdunal swales in neutral to moderately alkaline sands of Pleistocene and to Holocene barrier islands” (Singhurst et al. 2011); Aransas (Singhurst 18338, BAYLU) and Calhoun (Singhurst 18336 holotype: BAYLU; isotypes: BRIT, TEX]; Singhurst, Hanks, and Hensen 18339, 18340, 18341, 18342, and 18343 [all BAYLU]) cos. in the TX Coastal Bend; endemic to coastal TX (however, there are reported but unconfirmed occurrences in LA and MS—J. Singhurst, pers. comm.). Sporulating Jun and Oct (collections known only from these months). Singhurst et al. (2011) noted that “The new species resembles Isoëtes flaccida A. Braun of Florida and Georgia and keys near its vicinity in both Lellinger (1985) and Taylor et al. (1993). The resemblance is mainly expressed in length of the leaves and aquatic habitat.” However, Isoëtes flaccida has microspores with tuberculate to prominently rugulate surfaces and bright green leaves and is separated geographically from I. texana by about 1200 km (746 mi). This species is one of only two pteridophytes endemic to TX (the other is I. lithophila). Isoëtes texana is the most recently described species of the TX flora—the publication date is 5 May 2011 (Singhurst et al. 2011). The species is of conservation concern; Singhurst et al. (2011) consider it globally rare with a ranking of G1S1. They note that “Immediate threats to this species include development and expansion of ponds for livestock use and human recreation (fishing). The population in Aransas National Wildlife Refuge in Aransas County is well protected. The Calhoun County occurrences are on private land and appear to be reasonably secure at this time. Rising sea level may present a long-term threat to the species as they appear susceptible to salt water intrusion.” (Singhurst et al. 2011: G1S1)

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