Pilularia L.
Descripción
Rhizomes long-creeping, slender, bearing hairs, roots arising at nodes; leaves filiform, circinate, terete, lacking expanded blades, with a single vascular strand, glabrous; sporocarps produced only on emergent plants, globose, indurate, borne singly at or just above ground level on unbranched stalks arising at bases of petioles, attached laterally to stalk apex (attached portion called raphe), lacking teeth, densely to sparsely hairy, hairs abraded with age, dehiscing into 4 valves; sori 2–4 per sporocarp; sporangia of two kinds: ovoid megasporangia, containing single megaspores, and fusiform microsporangia, containing numerous microspores; indusia thin, enclosing the sporangia; megaspores ovoid, filling the megasporangia, with a prominent papilla-like laesura, surface rugulose; microspores tetrahedral-globose, surface densely and coarsely rugose; x=10.A
Forma de vida
Hidrófita enraizada, TerrestreA
Distribución
México (país) Nativo y no endémicoA
Ecología y Hábitat
Aquatic or in shallow seasonally drying pools, rooted in soil.A
Categoría IUCN
No incluidaB
Categoría NOM-059-SEMARNAT-2010
No incluidaC
Discusión taxonómica
Pilularia comprises about five very similar species, distributed in North America, South America, Europe, Australia, and New Zealand. The discreteness and interrelationships of species within Pilularia need re-investigation using modern methods. The genus is closely related to two other genera of heterosporous ferns, Marsilea (which see, for discussion of relationships within the family) and Regnellidium, the latter monotypic and restricted to southeastern Brazil and northeastern Argentina. Together, these three genera constitute the family Marsileaceae, which is now believed to be allied to the other two heterosporous fern genera, Salvinia and Azolla (Pryer et al., 1995; Pryer, 1999).A