Dicksonia L’Hér., Sert. Angl.

Lehnert, Marcus & Kessler, Michael, 2018, Prodromus of a fern flora for Bolivia. XXI. Dicksoniaceae, Phytotaxa 344 (1), pp. 69-74 : 70-71

Dicksonia L’Hér., Sert. Angl. : 30, p.p. 1789.

In continental South America Dicksonia comprises five species (Noben et al., unpublished data) that form a clade sister to Australian D. antarctica Labill. and allies ( Noben et al. 2017). These share a similar appearance, having usually unbranched, erect trunks with vascular tissue arranged in a corrugated dictyostele, and monomorphic fronds with oblanceolate (rarely elliptic) blades on relatively short petioles. They also have the same spore type, which is slightly depressed between the laesural arms and covered with a thin, granular to bacillar perine. Paleotropical species, to which the endemics of the Juan Fernández Islands, Chile, are phylogenetically related ( Noben et al. 2017), differ in certain aspects, mostly having trunks with a solenostele, longer petioles, more ovate blades, and spores with an areolate perine. Frond dimorphism is common among paleotropical taxa, in some species very pronouncedly so ( Noben & Lehnert 2013).

Most species are considered diploids with a chromosome number n = 65 ( Roy & Holttum 1965, Dawson et al. 2000) but there is one report of a tetraploid, a Javanese plant with n = 130 ( Lovis 1978). These cytological studies included all major clades of Dicksonia ( Noben et al. 2017) but no South American species. Further studies on genome size may shed light on the unresolved young radiation of the Andean taxa ( Noben et al. 2017, unpublished data), especially illuminating the possibility of hybridization ( Moore 1885).

In Mexico ( Eleutério & Pérez-Salicrup 2006), Guatemala ( Véliz & Vargas 2006), and southeastern Brazil ( Sehnem 1978, Windisch 2002), the genus is extracted from the wild for making ornamental flowerpots or for use as ornamentals. To curb the exploitation of the wild populations, the South American species are all listed under CITES (Appendix II, www.cites.org) and additionally protected by national law in several countries.

Dicksonia is found mostly in the understory of cool tropical montane forests from ca. 1000 m to tree line, also at lower elevations in southern temperate regions, sometimes in open vegetation on ridges or on islands where regular mists provide a cool, humid environment. Populations vary in density and seem to be supported mainly by spores. Vegetative reproduction by buds is not observed in Bolivian populations and has been documented in the Neotropics only for D. navarrensis Christ from Colombia (as D. sellowiana, Calderón-Sáenz 2000 ) and Panamá (M. Lehnert, pers. obs.). Interestingly, these vegetatively reproducing plants are scattered in the forest and do not form dense colonies. At some localities, however, Dicksonia can be dominant to the exclusion of other species in the forest understory, e.g., Dicksonia sellowiana in Brazil near the town of Urubici, Santa Catarina state, (www.fernsoftheworld.com) and D.

karsteniana in Bolivia in the Reserva La Yunga, Dept. Santa Cruz (Lehnert, pers. obs.). The latter locality lies at the so-called Andean knee or deflection in central Bolivia, where Andean montane rainforest comes closest geographically to the similar Brazilian Atlantic rainforest, or Mata Atlântica; in both areas, Dicksonia is a regular element of the understory and there are many biogeographic disjunctions between them at the species level in ferns, e.g., Cyathea ( Weigand & Lehnert 2016) , Melpomene ( Lehnert 2008) , and Serpocaulon ( Kreier et al. 2008) , and other plant groups ( Fiaschi & Pirani 2009).