Pteridium
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Authority
Mickel, John T. & Beitel, Joseph M. 1988. Pteridophyte Flora of Oaxaca, Mexico. Mem. New York Bot. Gard. 46: 1-580.
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Family
Dennstaedtiaceae
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Scientific Name
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Description
Genus Description - Terrestrial; rhizome long-creeping, subterranean, with hairs; fronds medium-sized to very large; stipe long, smooth to short-hairy, the base not strongly distinct from the rhizome, with branch buds near the base, with nectaries at the base of first and sometimes upper pairs of pinnae; blade broadly deflate, 2-4 times pinnate, the basal pinnae often exaggerated basiscopically, each basal pinna nearly equal to upper part of frond in size; lamina chartaceous to coriaceous, sparsely to densely hairy beneath; veins free, forking, except connecting beneath sori; sori marginal with a differentiated recurved marginal false indusium and a very slight inner indusium; spores tetrahedral-globose, brown.
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Discussion
Type: Pteridium aquilinum (Linnaeus) Kuhn [=Pteris aquilina Linnaeus]. Pteridium is treated as a single widespread species with several regional varieties (R. Tryon, 1941) or as several distinct species. Four taxa occur in Mexico, but only three in southern Mexico. The plants are generally aggressive, invading disturbed areas as common weeds in pastures, cultivated fields and roadsides. The genus is closely allied to Paesia and Hypolepis. Pteridium is distinguished by its hairy rhizome well beneath the soil surface, coriaceous blade, vestigial inner indusium and tetrahedral spores. The three taxa of Pteridium in Oaxaca are separated by distinct sets of characters which are consistent throughout, except for a few individual plants that combine the sets of two species. Since these characters remain consistent even when two or more taxa grow sympatrically (an excellent example being a cut-over site in Dist. Teotitlán, 2020 m, at which P. arachnoideum (4543), P. caudatum (4542), and P. feei (4541) occur), it seems better to treat the taxa as species rather than as varieties, which should, in the modem sense of varieties and subspecies, replace each other in areas of overlap. The individual collections that combine the characters of two taxa are treated as hybrids. Field studies and modem biosystematic studies are needed in Pteridium. The descriptions under the three taxa include only those features in which that taxon differs from the others. References: Perring, F. H. & B. G. Gardener (eds.). 1976. The biology of bracken. J. Linn. Soc., Bot. 73: 1-302 (papers by several authors); Tryon, R. 1941. Revision of the genus Pteridium. Rhodora 43: 1-31, 37-70 (reprinted in Contr. Gray Herb. 134: 1-31, 3770. 1941).