Danaea Sm., Mem. Acad. Roy. Sci.

Tuomisto, Hanna, Kessler, Michael & Smith, Alan R., 2018, Prodromus of a fern flora for Bolivia. VIII. Marattiaceae, Phytotaxa 344 (1), pp. 64-68 : 65

Danaea Sm., Mem. Acad. Roy. Sci. (Turin) 5: 420, p. 9, f. 11. 1793.

Danaea is confined to the Neotropics. It is easily recognized as belonging to the Marattiaceae by the presence of pseudostipules on the rhizomes, pulvini, and rachis nodes, and can be differentiated from the other genera in Marattiaceae by the usually once-pinnate leaves (rarely simple or irregularly bipinnate) with opposite pinnae, and clearly dimorphic leaves with the fertile leaves having more contracted blades but longer petioles than the sterile ones ( Brebner 1902, Underwood 1902, Tuomisto & Moran 2001). The fertile leaves are relatively short-lived and have sunken synangia, which are generally arranged along the secondary veins and cover almost the entire abaxial surface of the pinnae. Sometimes, aberrant leaves with partly fertile and partly sterile pinnae can be found. Individual sporangia within the synangia open by apical pores. Sterile leaves are long-lived and often covered in epiphyllous mosses and lichens.

Characteristics of the rhizomes are important for species identification and should always be documented when making herbarium specimens. The most widespread (and probably ancestral) kind of rhizome is an erect trunk, which has leaf bases arranged spirally and stilt-like roots on all sides. This is the only kind of rhizome found in the subg. Arthrodanaea C.Presl, and it is also present in several species of both other subgenera (subg. Danaea and subg. Holodanaea C.Presl). There are many interspecific differences in both the height (from 0.1 m to over 1 m) and the sturdiness of the trunks. Species of subg. Danaea that do not have erect trunks have instead short-creeping, compact rhizomes that are clearly dorsiventral: all leaf bases are on the upper side and are arranged in two or more rows, and all roots are on the lower side. Subg. Holodanaea is the most variable in terms of rhizome structure: some species have an erect trunk, others a dorsiventral creeping rhizome, and still others have an intermediate decumbent rhizome type, in which the rhizome itself is horizontal but leaf bases are arranged spirally and the very apex of the rhizome may be bent upwards. Species limits within Danaea are often difficult to define, but the subgenera are relatively easy to recognize. Therefore, subgeneric membership is indicated (in parentheses) for each species in the treatment below.

Phylogenetic analyses place Danaea as sister to the remainder of Marattiaceae ( Murdock 2008a) , but the isolated position of the family makes this conclusion tenuous ( Murdock 2008b). We disagree with the very broad species circumscriptions of Rolleri (2004), who treated Danaea as including only 17 species. Instead, we apply a narrower taxonomic concept (mostly following, but not identical with, Tuomisto & Moran 2001; Christenhusz & Tuomisto 2005, 2006; Christenhusz 2010a). Our current estimate is that Danaea comprises at least 50 species. In Amazonia, where several species co-occur, there is a clear ecological separation of species by soil characteristics, especially nutrient concentration and drainage ( Tuomisto & Poulsen 1996; Christenhusz & Tuomisto 2005), which presumably also played a role in the diversification of the genus (Christenhusz et al. 2008).