Dicksonia
Distribution
Asia-Tropical: Jawa (Jawa present); New Guinea present; Philippines (Philippines present); Sulawesi (Sulawesi present); Sumatera (Sumatera present), Australasia: Tasmania (Tasmania present), E. Australia present, Malaysia present, N. Borneo present, New Caledonia present, New Zealand present, Northern America, Pacific: Fiji (Fiji present); Samoa (Samoa present), S. America present, St Helena present
About 25 spp. St Helena; S. America and north to Mexico; New Zealand, E. Australia and Tasmania, New Caledonia, Samoa, Fiji; in Malaysia: New Guinea, Celebes, Philippines, N. Borneo, Java, and Sumatra.
Morphology
The trunk of Dicksonia is closely similar in form and anatomy to that of Cyathea, from which Dicksonia differs by the indument consisting entirely of hairs. For comment on the possible relationships between the very different soral forms in the two genera, see p. 69.
Taxonomy
The history of the varied use of the generic name Dicksonia is summarized by Maxon, l.c. Earlier authors confused not only Dicksonia, Culcita and Cibotium, but also Dennstaedtia and other genera now recognized as distinct. Within the genus, the discrimination of species is difficult because the soral form is so constant and the Variation in shape of tertiary leaflets as between those on larger or smaller pinnules in one species may be considerable. The character of the hairs on the stipe appears to be one of the clearest distinctions between species, as are scale-characters in Cyathea; but the differences between one hair and another are less easily defined than those between different scales. The species in New Guinea are particularly difficult to discriminate, and the present account can only be regarded as tentative; more field Observation is needed.