Pilularia americana

Pilularia americana A. Braun
(of America)

Local names: American pillwort, water-pepper

Small inconspicuous aquatic, submersed or infrequently persisting on bare mud; leaves filiform, 1.6–10.2 cm long, lacking expanded blades; sporocarps produced just below ground surface, globose, 2–6(–10) mm long, 2–3 mm in diam.; 2n = 20 (Chopra 1960). Temporary pools, ponds, tanks, and reservoir margins; J. Peck (pers. comm.) indicated that the best time to find this species is after reservoir drawdowns in fall. According to the range map in Johnson (1993a), P. Americana occurs rather broadly in nc TX, the n part of e TX, and the n part of c TX; the only confirmed records we know of are from Burnet (R. McVaugh 7656, Granite Mt.—BRIT, TEX-LL), Colorado (J.&C. Taylor 32117, J. Taylor 32127, BRIT), Llano (D. Seigler et al. 2016, Enchanted Rock, TEXLL), Mason (S.R. Hill 8654, BRIT, TEX-LL, T. Walters 795, BRIT), Smith (O’Kennon 19989, BRIT), Tarrant (O’Kennon 22097, Fort Worth Nature Center & Refuge, BRIT), and Wise (O’Kennon & McLemore 18341; BRIT) cos.; AR, CA, GA, KS, MO, NE, OK, OR, TN, and TX; also Baja California and Durango in Mexico and South America (Mickel & Smith 2004). Sporocarps produced late spring–fall. Weakley (2010) noted that, “This peculiar plant has a puzzling distribution, being known from several disjunct regions: OR to s. CA; NE to TX; AR; TN; and GA to SC.” It is so inconspicuous that it is rarely recognized or collected. A large population (ca 150 sq. m) was discovered in AR (Culwell 1994), prompting the comment that the species “may be more common than herbarium specimens indicate” (Culwell 1994). The population was growing in shallow water in a large lake; Culwell (1994) in describing the AR population noted “after the lake had undergone a drawdown, I noticed a large area…, usually under approximately 8–16 cm of water, that appeared to be a bluegrass lawn. This expanse extended about 6 m from the original shoreline at a gradual slope and stretched approximately 25 m along the shore. The population was quite dense and a relatively pure stand, with few invading species.” Mickel and Smith (2004) also suggest that because of “its inconspicuous and unfern-like appearance, probably it has been overlooked by collectors.” This species was long known in TX only from the Central Mineral Region (e.g., Correll 1956; Turner et al. 2003). Recently, however, Bob O’Kennon (pers. comm.) has found extensive colonies in Lake Tyler (Smith Co. in East TX) and in Tarrant and Wise cos. (in the Cross Timbers and Prairies), and specimens are known from Colorado Co. The Smith, Tarrant, and Wise populations were found on exposed flats during a period of extreme low water following prolonged drought. The plants had presumably been living for many years entirely underwater. Extensive searching in similar nearby habitats did not reveal additional colonies. A reasonable hypothesis for this sporadic appearance is long-distance dispersal of the sporocarps or spores inside of or on the feet of waterfowl. Such dispersal can apparently occur for related Marsilea species (Johnson 1986; Mickel & Smith 2004). Recent molecular research (Nagalingum et al. 2008) has found that this species consists of two geographically and genetically distinct groups and needs further study. Weakley (2010) pointed out that the plant “may be recognized as a ‘fern’ by the typical coiled (‘fiddlehead’) development of young leaves.”

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