New Zealand has a new tree fern – kind of.
Te Papa Research Fellow Patrick Brownsey and I have recently recognised a subspecies within the stumpy tree fern, tuokura, Dicksonia lanata. The new name is Dicksonia lanata subspecies hispida.
It is only kind of a new tree fern, as it was first recognised as something different way back in 1844! When William Colenso first described Dicksonia lanata, he thought it contained two entities, naming one Dicksonia lanata variety hispida.
Colenso’s hispida name was largely subsequently ignored, possibly because he did not provide much detail. However, it has long been appreciated that Dicksonia lanata is unusually variable.
Populations north of Auckland produce a short trunk, to about 2 m, whereas those to the south have no truck at all; i.e., the latter are a trunk-less tree fern! But is this because they are different entities, or because populations in colder areas do not form a trunk?
A molecular investigation by Robbie Lewis at Massey University about 15 years ago indicated that the northern trunked and southern trunk-less plants were genetically distinguishable. Subsequently, Pat and I have worked out additional external features by which to separate them – their hairs are particularly useful.
After our study, we think the northern trunked and southern trunk-less plants should be classified differently, but at the rank of subspecies, entailing a ‘new name’. The taxonomic rank of subspecies is often used for distinguishable but geographically-separated lineages. By contrast, the rank of variety, although popular in Colenso’s day, is now little used, as it has no clear meaning.
The two subspecies
Dicksonia lanata subspecies lanata occurs from the Coromandel southwards through the North Island and along the northern and west coasts of the South Island. It doesn’t form a trunk. The hairs on the underside of the frond are in obvious ‘woolly’ tufts (hence the Latin lanata). It can dominate the ground cover under forests in colder areas (e.g., Urewera ranges).
Dicksonia lanata subspecies hispida occurs from North Cape to Kaipara and Great Barrier Island. It forms a short trunk, up to about 2 m tall. The hairs on the underside of the frond are not tufted but more uniformly distributed. It is often found in kauri forest.
Limited access to the full paper is available here. If this doesn’t work, email me for a copy of the paper.