Mickel, John T. & Smith, Alan R. 2004. The pteridophytes of Mexico. Mem. New York Bot. Gard. 88: 1-1054.
Thelypteridaceae
Genus Description - Terrestrial to rarely epipetric or epiphytic; rhizomes longcreeping to short-creeping to erect, dictyostelic; rhizome scales entire and usually ciliate on the margins and/or surfaces; fronds simple to pinnate to usually pinnate-pinnatifid, to decompound (Old World groups); stipes in cross section with two crescentshaped vascular bundles at bases, these fusing distally; blade axes (stipes, rachises, and costae) adaxially sulcate, grooves not running continuously into axis of the next order; indument of stipes, blades, and/or rachises nearly always hairy, sometimes sparingly, at least in the adaxial grooves, often on axes and leaf tissue abaxially, hairs acicular (unicellular or multicellular), hamate, or stellate; sori dorsal on the veins, occasionally submarginal, with or without reniform indusia; spores bilateral (tetrahedral in a fewOld World species), with a usually prominent perispore; x=36, 35, 34, 33, 32, 31, 30, 29, 27.
Type: Thelypteris palustris Schott [=Acrostichum thelypteris L.]. Some authors adopt Thelypteris thelypteroides (Michx.) Holub as the name for this taxon, but Tryon and Tryon (1973) argued against this.
In its broadest sense, Thelypteris comprises nearly 1000 species, distributed pantropically but with a few species in temperate areas. Using a broad circumscription, there are perhaps 300 species of Thelypteris in the Neotropics. In its narrowest sense, Thelypteris includes only two species, one (T. palustris) in Mexico. Distinguishing characters of Thelypteris include the stipe vasculature of two bundles (many bundles in dryopteroid ferns); acicular hairs on many parts of the frond; usually bilateral spores with a prominent perispore; and chromosome base numbers from 27 to 36 (x=40, 41 in dryopteroids and athyrioids). Thelypteris s.l. has been subdivided by pteridologists into natural groups variously treated as genera, subgenera, or sections. Most of the New World groups can be well circumscribed using a combination of characters, and thus could stand as genera, but we segregate only one of these, Macrothelypteris, naturalized in the New World, in this flora. For now, the interests of taxonomists and other biologists seem best served by adopting a large genus Thelypteris with several subgenera. Those subgenera occurring in Mexico can be distinguished by the key following the references. Species are individually keyed under each subgenus. Although precise relationships are still unresolved, Thelypteris s.l., in the sense applied here, and Thelypteridaceae, are hypothesized to have sister group relationships with a suite of athyrioid, blechnoid, onocleoid, and woodsioid ferns (Smith & Cranfill, 2002). The family comprises two main lineages, one phegopteroid (including Macrothelypteris, which see) the other thelypteroid (including Thelypteris s.l. and Cyclosorus s.l., the latter including the segregate genera Goniopteris, Meniscium, Steiropteris, and Stegnogramma in Mexico). All segregates possessing x=36 (Cyclosorus sensu Smith in Kubitzki, 1991), form a strongly supported clade in a recent analysis (Smith & Cranfill, 2002); these species also usually have veins that either unite below the sinuses or run to the sinuses. The free-veined species groups (Thelypteris sensu Smith in Kubitzki, 1991), with lower base chromosome numbers, include both Amauropelta and Thelypteris s.str. in the Neotropics; these groups insert below Cyclosorus in the hypothetical phylogenetic tree.