Mickel, John T. & Smith, Alan R. 2004. The pteridophytes of Mexico. Mem. New York Bot. Gard. 88: 1-1054.
Athyriaceae
Genus Description - Terrestrial; roots stout and somewhat fleshy; rhizomes usually suberect to erect (caudices sometimes trunk-like), scaly; fronds medium-sized to often large, monomorphic, not articulate; stipes usually glabrous, scaly at bases, with two crescent-shaped vascular bundles in cross section; blades thin-herbaceous to chartaceous or subcoriaceous, usually pinnate to 2-3-pinnatepinnatifid, sometimes 4 (plus/ minus) pinnate, rarely simple, some species producing buds in axils of blade bases, pinnae, or pinnules, these sometimes developing into plantlets; veins generally free, rarely casually to abundantly anastomosing, pinnate in the ultimate segments or sometimes strongly curved toward blade margins and appearing parallel; indument abaxially of brownish to tan scales on rachises, costae, and costules, sometimes also of hairs, these often septate, adaxially the blades glabrous or with short papillae or hairs ca. 0.1 mm (or less) in rachial, costal, and costular grooves; sori abaxial, linear or oblong on the veins, usually with at least some of them (sometimes only the basal ones) backto-back (diplazioid) on a single vein; indusia generally covering each sorus, rarely absent, paraphyses absent; sporangia shortstalked, stalks less than half the length of capsules; spores bilateral, with winged perispores; X41.
Lectotype (chosen by J. Smith, Hist. Fil. 325. 1875): Diplazium plantaginifolium (L.) Urb. [= Asplenium plantagineum L.].
Diplazium comprises 350–400 species, with probably more than 150 in the NewWorld; it is generally a genus of wet tropical forests of low to middle (rarely high) elevations. Twenty-five species are known from Mexico. Chromosome counts for species range from diploid, 2n=82, to octaploid, 2n=328. Judging by the number of intermediate specimens that show malformed spores and a few chromosome counts, hybridization is apparently common in the genus, at least in the Neotropics. Putative hybrids have been suggested between species in Ecuador (Stolze et al., 1994) and Mexico (Mickel & Beitel, 1988; Smith, 1981). Monographic studies are needed for a better understanding of the species and their relationships. Diplazium is distinguished by its commonly indusiate sori (among Mexican species, indusia are absent, or nearly so, only in D. lindbergii) that are elongate and at least sometimes back-to-back along the veins, relatively thick roots, suberect to erect rhizomes, two ribbon-like vascular bundles in the petioles, and a chromosome base number of x=41. At least half of the Mexican species have distinctive papillae 0.05–0.1 mm long in the rachial, costal, and costular grooves adaxially. Relationships of the genus are with the athyrioid ferns, especially Athyrium and a number of Old World genera usually now segregated from Diplazium and Athyrium, e.g., Callipteris, Cornopteris, and Deparia. Diplazium has more distant relationships with Onocleopsis and the onocleoid ferns, and, beyond that, with the blechnoid ferns (Cranfill, unpubl.).