Pteridium
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Authority
Mickel, John T. & Smith, Alan R. 2004. The pteridophytes of Mexico. Mem. New York Bot. Gard. 88: 1-1054.
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Family
Dennstaedtiaceae
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Scientific Name
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Description
Genus Description - Terrestrial; rhizomes long-creeping, subterranean, with hairs; fronds medium-sized to very large; stipes long, glabrous to shorthairy, the bases not strongly distinct from the rhizomes, with branch buds near the bases; blades broadly deltate, 2–4-pinnate, the basal pinnae often exaggerated basiscopically, each basal pinna nearly equal to distal part of blade in size, with nectaries at the base of first and sometimes distal pinna pairs; laminae chartaceous to coriaceous, sparsely to densely hairy abaxially with straight to lax hairs, often with scattered minute 2-celled hairs adaxially; veins free, forking, ends fusing at soriferous margins; sori marginal with differentiated recurved marginal false indusia and sometimes very slight inner, extrorse indusia; spores tetrahedral-globose, brown; x=52.
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Discussion
Type: Pteridium aquilinum (L.) Kuhn [= Pteris aquilina L.].
Pteridium has been treated as a single widespread species with several regional varieties (Jacob & Peck in FNA Ed. Comm., 1993; R. Tryon, 1941) or as several distinct species (Moran in Davidse et al., 1995; Mickel & Beitel, 1988). Three species, one including three varieties, occur in Mexico. The plants are generally aggressive, invading disturbed areas as weeds in pastures, cultivated fields, and roadsides. The genus is closely allied to Paesia and Hypolepis. Pteridium is distinguished by its hairy rhizomes well beneath the soil surface, coriaceous blades, vestigial inner indusia, and tetrahedral spores. Throughout much of Mexico, Pteridium arachnoideum, P. caudatum, and P. aquilinum var. feei are separated by correlated characters, except for a few individual plants that combine character states of two species. Since these character states remain consistent even when two or more taxa grow sympatrically (Mickel & Beitel, 1988), it seems desirable to treat them at species rank. This view is supported by Thomson’s (2000) conclusions based on morphological and molecular data. Taxa here treated as varieties of Pteridium aquilinum (vars. feei, latiusculum, and pubescens) appear closely allied by their long, lax hairs, and have more or less allopatric distributions. There is wide variation in degrees and type of pubescence between and sometimes within taxa. Collections that combine the characters of two varieties are treated as hybrids. In the few fertile specimens, the spores appear to be well formed and the characters seem to be so variable. Field studies and modern biosystematic studies are needed in Pteridium.