Alsophila R.Br., Prodr. Fl.

Lehnert, Marcus & Kessler, Michael, 2018, Prodromus of a fern flora for Bolivia. XX. Cyatheaceae, Phytotaxa 334 (2), pp. 118-134 : 120

Alsophila R.Br., Prodr. Fl. Nov. Holland. 158. 1810.

= Gymnosphaera Blume, Enum. Pl. Javae 2: 242. 1828.

= Nephelea R.M.Tryon, Contr. Gray Herb. 200: 37. 1970.

Alsophila comprises ca. 275 species following the circumscription of Conant (1983) and Smith et al. (2006). The species are characterized by marginate petiole scales with at least one apical seta, being one enlarged cell with thick, darkened cell walls that is supported by several cells. Most neotropical species have narrow-lanceolate to almost filiform petiole scales with undulate-crispate margins that can bear additional lateral dark setae. The spores are generally of a very bright yellow color, and the perispore ornamentation shows little variation between species (either ridged or finely cristate). In Bolivia, species of Alsophila typically have narrow, brittle, black spines that are very different from the thick, green to brown spines found in some species of Cyathea .

The genus Alsophila falls into two distinct clades in all phylogenetic reconstructions, Alsophila s.s. and the Gymnosphaera clade, and each receives high support as natural group. Depending on sample size (Lehnert et al., unpubl. data) and analytical method ( Korall & Pryer 2014), the sister group relation between these clades and the genus Cyathea varies and no reconstruction receives optimal support for all relevant nodes. Morphologically, Gymnosphaera can be regarded as having only plesiomorphic characters that have been modified in Alsophila (16 spores per sporangium vs. 64 in Gymnosphaera ) and Cyathea (marginal/apical setae on scale margins absent vs. present), so any sister group relationship between the three can be interpreted as equally plausible. We here adhere to the broader circumscription of Alsophila for reasons of nomenclatural parsimony and continuity until new molecular results unambiguously necessitate doing otherwise. In the Neotropics, the Gymnosphaera clade is only represented by two species: A. capensis (L.f.) J.Sm. subsp. polypodioides (Sw.) D.S.Conant , restricted to southeastern Brazil, and A. salvinii Hook. , found regularly in Mesoamerica and scattered in Peru and Brazil; neither has been recorded for Bolivia yet.

In total, Alsophila has 36 species with 6 varieties in the Neotropics; half of the species are endemic to the Greater Antilles and there is almost no overlap in species composition with continental South America ( Gastony 1973, Conant 1983). Five species are known from Bolivia. In the Antilles, hybrids between species of Alsophila are not rare ( Conant & Cooper-Driver 1980, Caluff & Serrano 2002). No hybrids have yet been recorded in continental America, but it is likely that they may eventually be found. In Africa and Australasia, Alsophila is the most diverse tree fern genus and occupies most of the ecological niches that Cyathea does in the Neotropics. There, Alsophila also has a much greater morphological variability than in the Neotropics.

Many neotropical species of Alsophila reproduce by rhizomes, forming dense clonal populations. In Mexico, A. firma (Baker) D.S. Conant drops most leaves in the wet season, perhaps as a protection against herbivores ( Mehltreter & García-Franco 2008). In southeastern Brazil, A. setosa Kaulf. shows a similar increased leaf turnover at the start of spring ( Schmitt & Windisch 2006). This has not yet been observed among Bolivian species, but we have seen largescale leaf mortality as the result of extreme frost events (M. Kessler, pers. obs.).