Nephrolepis Flexuosa Colenso Reinstated For New Zealand’s “Geothermal” Nephrolepis
The indigenous Nephrolepis associated with active geothermal systems of the Taupo Volcanic Zone of the North Island of New Zealand has for many years been referred to N. cordifolia (L.) C.Presl, as that species, a “variant” or “ecotype” of it, or as an unnamed entity allied to it. In the June 2005 issue of the New Zealand Journal of Botany (Vol. 43(2)), the name N. flexuosa Colenso has been reinstated for this fern (de Lange et al. 2005). In that paper it is noted that N. flexuosa differs from N. cordifolia by its narrower fronds, larger spores, lack of root tubers, and distinctive chromosome number (2n = 164 cf. 2n = 82 in N. cordifolia). Outside New Zealand de Lange et al. (2005) accepted N. flexuosa from Raoul, Norfolk, Lord Howe, and the Fijian Islands. Recently (May 2005) it has also been discovered on Rarotonga, and it seems very likely that it is even more wide ranging than this, as literature accounts from throughout the Pacific and Indian Oceans, and from Australia frequently mention a form of N. cordifolia “lacking root tubers”.
From a conservation perspective, N. flexuosa as N. aff. cordifolia (AK 232904; “thermal”) has been listed as “Taxonomically Indeterminate, At Risk/Range Restricted” (de Lange et al. 2004) but with the application of a formal, legitimately, and effectively published name, a review of its status seems appropriate. Based on that review N. flexuosa now qualifies for “Chronically Threatened/Gradual Decline” because in the North Island part of its range it has recently gone extinct at several locations around Lake Taupo and some populations north of there have dwindled in size, mainly, it is suspected, through competition from taller growing weeds. However, N. flexuosa remains abundant at the Waimangu, Waiotapu, Wairakei and at Lake Rotomahana in the Rotorua region, and it is very common on Raoul Island. Outside New Zealand it is close to extinction on Norfolk Island but is very common on Lord Howe, while its status on the Fijian Islands and Rarotonga is unclear. For this reason the qualifier “DP – Data Poor seems appropriate”.
References
de Lange, P.J.; Gardner, R.O.; Crowcroft, G.M.; Stalker, F.; Cameron, E.K.; Braggins, J.E; Christian, M.L. 2005: Vascular flora of Norfolk Island: some additions and taxonomic notes. New Zealand Journal of Botany 43: 563-596.
de Lange, P.J.; Norton, D.A.; Heenan, P.B.; Courtney, S.P.; Molloy, B.P.J.; Ogle, C.C.; Rance, B.D.; Johnson, P.N.; Hitchmough, R. 2004: Threatened and uncommon plants of New Zealand. New Zealand Journal of Botany 42: 45-76.
Posted: 05/07/2005