Didymoglossum Desv., Mém. Soc. Linn. Paris

Kessler, Michael & Smith, Alan R., 2017, Prodromus of a fern flora for Bolivia. X. Hymenophyllaceae, Phytotaxa 328 (3), pp. 201-226 : 204

Didymoglossum Desv., Mém. Soc. Linn. Paris 6: 330. 1827.

= Microgonium C.Presl , Hymenophyllaceae (Presl) 19(–20). 1843 [ Abh. Königl. Böhm. Ges. Wiss., ser. 5, 3: 111. 1843].

Didymoglossum , a segregate of Trichomanes , comprises about 35 species, slightly more than half of them in the Neotropics, the remainder in Africa, on islands of the Indian Ocean, and in southeast Asia, Malesia, and Polynesia. The American species, about 20, were revised by Wessels-Boer (1962); a few species have been described since then. Ebihara et al. (2006) recognized two subgenera, Didymoglossum and Microgonium , distinguished by the presence in the latter of submarginal false veinlets (such veinlets absent in subg. Didymoglossum ); in Bolivia, subg. Microgonium includes only a single species, D. kapplerianum .

Species of Didymoglossum are small, usually with leaves 0.3–12 cm long, characterized primarily by having false, unconnected veins between the true veins. In some species, these veins also run along the blade margins. Other characters include long-creeping rhizomes, rhizomes bearing dark-colored hairs, the absence of true roots, the presence of false veinlets parallel to, and not connected with, the true veinlets, catadromous blade venation (basiscopic vein, in a vein-group, arising first), conical involucres (often with darkened lips), and a chromosome base number of x = 34 (unique in the Hymenophyllaceae ). The species are epiphytic or epipetric on mossy rocks. The genus appears to be most closely related, and sister to, the combined pantropical clade Crepidomanes + Vandenboschia ( Ebihara et al. 2006; Pryer et al. 2001).