A New Revision For Ladder Ferns (Nephrolepis: Nephrolepidaceae) Affects Two New Zealand SpeciesA recently published paper (Hovenkamp & Miyamoto 2005: A conspectus of the native and naturalized species of Nephrolepis (Nephrolepidaceae) in the world, Blumea 50(2): 279-322) refers all Kermadec Island gatherings of the fern previously known here as N. hirsutula (G.Forst.) C.Presl and N. exaltata (L.) Schott to another species N. brownii (Desv.) Hovenkamp et Miyam. That treatment also refers the newly reinstated N. flexuosa Colenso to N. cordifolia (L.) C.Presl. var. cordifolia.
The referral of Kermadec Island plants to N. brownii is backed by sound morphological characters which include the nearly entire acumen and hyaline or light brown (rarely rufous) rachis scales, submedial sori, and presence of costal hairs along the upper surface of pinnules. In their paper they imply that the species is native only to Malesia and naturalised elsewhere but no clear evidence is provided to support that view. So we continue to regard it as indigenous. N. hirsutula they point out is a widely misapplied name. That species they distinguish from N. brownii by the absence of costal hairs on the upper pinnule surfaces, rufous rachis scales whose acumen is conspicuously dentate, and by the submarginal sori.
With respect to N. flexuosa, they refer this species to N. cordifolia var. cordifolia with minimal comment. However, their revision, which includes chromosome data and spore sizes as critical characters does not cite literature showing that N. flexuosa has larger spores than N. cordifolia, and is 4x rather than 2x (x = 41, 2n = 82 in N. cordifolia, 2n = 164 in N. flexuosa). With respect to root tubers, considered in New Zealand at least, to be a useful field character distinguishing N. cordifolia from N. flexuosa, they suggest that tubers are not consistently produced, and imply that plants which produce tubers spread vegetatively and so one assumes are sterile. In New Zealand this is incorrect, tuberous N. cordifolia is sexually reproductive as well. NZPCN suggest that as there are two distinctive, morphological, and validly named entities in New Zealand there seems to be no good reason to refer them to the one species, which in this country is a serious weed.
Posted: 23 August 2005