Monographs Details: Hemidictyum
Authority: Mickel, John T. & Smith, Alan R. 2004. The pteridophytes of Mexico. Mem. New York Bot. Gard. 88: 1-1054.
Scientific Name:Hemidictyum
Description:Genus Description - Terrestrial; rhizomes stout, decumbent to suberect; rhizome scales brownish, subclathrate, with golden brown lumina; fronds monomorphic, 1–3(–5) m long, clumped; stipes stout, green to brown, glabrous, with 2 crescent-shaped vascular bundles in cross section; blades once-pinnate (odd-pinnate), blade apices conform, the pinnae oblong, glabrous; veins unforked or 1- forked near their bases, at nearly right angles to the costae, free near the costae, initially parallel and ca. 1–2 mm apart, forming a reticulate network in marginal half of the pinnae, areoles usuallyusually elongate, pentagonal or hexagonal, without included veinlets, network closed at margin by a continuous intramarginal vein; sori linear, along main vein branches between costae and first anastomoses, paraphyses absent; indusia lateral, linear, very narrow, membranous; spores bilateral, with folded sometimes sparingly perforate perispore; x=31.


Type: Hemidictyum marginatum (L.) C. Presl [= Asplenium marginatum L.].

Hemidictyum is a monotypic genus, the single species widespread in tropical America. Most specialists have thought it to be related to Diplazium (athyrioid ferns), but the chromosome number of x=31 is quite distinct from the base numbers of 40 and 41 prevalent in the athyrioid ferns. Recent unpublished molecular data by Cranfill indicate that Hemidictyum forms a clade with the diplazioid segregate genera Diplaziopsis (eastern Asia) and Homalosorus (Diplazium) pycnocarpon (Spreng.) M. Broun, in eastern United States, plus a similar Asian species D. flavoviride Alston), well apart from the core Diplazium; thus, the generic distinctness of Hemidictyum from Diplazium is strongly supported. Hemidictyum differs from Diplazium and Athyrium by the combination of large, once-pinnate fronds with subcordate-based pinnae, thin texture, netted veins, and long, indusiate sori.