Sticherus C.Presl, Tent. Pterid.

Kessler, Michael & Smith, Alan R., 2018, Prodromus of a fern flora for Bolivia. XI. Gleicheniaceae, Phytotaxa 344 (1), pp. 53-63 : 57

Sticherus C.Presl, Tent. Pterid. 51–52. 1836.

This is the largest genus of the family, including about 95 species of which about two thirds are found in the Neotropics, and the remainder in the Paleotropics. Sticherus is characterized by dormant buds with scales, simple or 1-forked veinlets, and pinnatifid or 1-pinnate ultimate branches. Species identification is mainly based on scale characters, with those of the buds, branches, midveins (main vein of each segment), and veinlets often differing considerably. Often, the distribution of darkened parts on individual scales is of diagnostic importance.

Species delimitation in Sticherus is problematic and not yet fully settled ( Ching 1940, Østergaard & Øllgaard 2001, Gonzales & Kessler 2011). Partly this is because many species show conspicuous morphological differences among plants growing in the full sun and those inhabiting more shaded spots. Those of drier habitats are typically somewhat smaller, with thicker-textured, narrower, and darker pinnae. Sticherus lechleri develops a dense whitish wax-like layer on the abaxial segment surfaces in sunny habitats, but not in humid sites, and the same may be true for other species. In southern Ecuador, S. bifidus , S. melanoblastus , and S. rubiginosus show great variability in size mainly due to different exposure to wind, light, and erosive energy (M. Kessler, pers. obs.). A detailed morphometric analysis of S. flabellatus R.Br. in Australia has similarly shown the presence of two broad ecotypes inhabiting closed forests and open forests, respectively ( Keiper & McConchie 2001). This variation does not correspond to genetic relatedness ( Keiper & McConchie 2000), demonstrating that is the result of the morphological adaptability of the individual plants, and that it is therefore of no taxonomic value (except at the level of varieties, which are not considered here).

The patchy and ephemeral nature of the habitats of Sticherus implies that the populations of a given species are often similarly patchy and short-lived. It can be assumed that many local populations are the result of a single or very few colonization events. In Australia, Keiper & McConchie (2000, 2001) have shown that most of the variation in genetic markers (AFLP) and photosynthetic pigments is found between populations, with little intrapopulation variability. Clearly, populations of Sticherus are dominantly inbreeding, with only occasional outcrossing between larger populations. This complex metapopulation structure implies that local populations may slightly differ morphologically and physiologically from each other. This intraspecific variability is one of the causes of the difficulties in delimiting species in this fascinating genus, but may also explain the adaptability of the species. In addition, there are numerous documented interspecific hybrids in Sticherus ( Duek 1974, Jermy & Walker 1985, Gonzales & Kessler 2011), further hindering species identification.