Isoëtes butleri

Isoëtes butleri Engelm
(for George Dexter Butler, 1850–1910, lawyer, teacher, botanist, and correspondent of George Engelmann, who discovered the species in what is now OK)

Local names: Butler’s quillwort

Leaves to 15(–30) cm long, dull green to gray-green or yellow-green, often lax and twisted, the outer surfaces white to tan or brown at base, not shiny; velum covering less than 1⁄4 of sporangium; megaspores white, the surfaces densely cobwebby, microscopically obscurely tuberculate; 2n = 22 (Taylor et al. 1993). Seasonally saturated soils, temporary or shallow pools, usually on calcareous soils, but also on sandstone or granite (in these cases there is probably a source of calcium nearby influencing pH—Lott et al. 1982); Mason (R. McVaugh 8322, BRIT, annotated K.D. Heafner 2005) and Llano (Correll & Johnston 17313, TEX-LL, annotated by W.C. Holmes & J. Singhurst 2004, SEM at TEX-LL; Lott et al. 1982), cos. on Llano Uplift of c TX and nearby Comal Co. (Turner et al. 2003), Sabine (Singhurst 11749, BAYLU) and San Augustine (Singhurst 11750, BAYLU) cos. on glauconite deposits (Weches Formation) in far East TX, and recently discovered in a number of counties in the Cross Timbers and Prairies (e.g., Tarrant Co, O’Kennon et al. 22367,BRIT; Bell and Coreyll cos., Hansen 2010). Norton Taylor et al. (2012) have recently greatly expanded the distribution of the species in TX by making collections in Bosque, Cooke, Denton, Erath, Hood, Johnson, Montague, Parker, Somervell, Williamson, and Wise cos. (specimens at BRIT). Collections are also known from a number of counties in Oklahoma—e.g., Choctaw, Johnston, and McCurtain cos. (Taylor & Taylor 1981) including some just across the Red River from TX; IL s to GA w to KS and TX. Spores mature in late spring. This species was reported as new to Texas by Lott et al. (1982). It was for many years known in TX only from the Llano Uplift of c TX but was later found to be disjunct to far East TX on the Weches Formation (Holmes et al. 2005). Very recently (2010–2012) it has been discovered as disjunct to a third region of TX, the Cross Timbers and Prairies in another geologically unusual setting—calcareous seeps on a number of limestone strata. For example, it was initially discovered on a “muhly seep” (= seeping calcareous slope dominated by the grass Muhlenbergia reverchonii, seep muhly) on the Walnut limestone; the identification has been confirmed based on SEM examination of megaspore ornamentation patterns (Tiana Franklin Rehman, pers. comm.). Taylor et al. (1993) noted that the “leaves yellow, wither, and disappear by late spring.” Unlike what is typical in Isoëtes (monoecious—developing megasporophylls early in the growing season and microsporophylls later), I. butleri is the only species known to be dioecious (Turner et al. 2005). This is one of several pteridophytes present in East TX with disjunct populations in the Central Mineral Region of the Edwards Plateau. Other examples are Ophioglossum crotalophoroides [bulbous adder’s-tongue], Ophioglossum nudicaule [slender adder’s-tongue], and Onoclea sensibilis [sensitive fern]. The inconspicuousness, visibility primarily in the spring, superficial similarity to a little tuft of some non-reproductively active grass or sedge, and habitat specificity of this species are probably the reasons explaining why there were relatively few collections in TX until recently.

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