Sequencing of Extinct Scurvy Grass Yields Unexpected ResultLepidium obtusatum Kirk appears to have been last collected in 1950 from the coastal cliffs near Seatoun, at the entrance to the Wellington Harbour. Intensive surveys for it there and along the southern Waitakere coast have not successfully located any further plants and it is believed extinct. Last week staff at the University of Auckland, together with Department of Conservation and Landcare Research scientists successfully obtained DNA sequences from a specimen of L. obtusatum collected from Seatoun in 1919! The results challenge current taxonomic opinion as to its nearest relatives…
The most recent assessment on the likely relationship of L. obtusatum Kirk was offered in 1995. That opinion, based on morphology, suggested that L. obtusatum was most closely allied to the “Acutely Threatened/Nationally Critical” L. banksii Kirk. As part of a taxonomic investigation into the Lepidium oleraceum complex Department of Conservation, Landcare Research and University of Auckland scientists successfully extracted and amplified DNA from a herbarium specimen collected by Arnold Wall from Seatoun in 1919. Using sequences from the nrDNA Internal Transcribed Spacer Region (ITS) and External Transcribed Spacer Region (ETS) staff were amazed to see that L. obtusatum is not closely allied to L. banksii or L. oleraceum s.s, instead it most closely related to an as yet unnamed Lepidium known from the Snares, Auckland and Southern Stewart Islands. This unnamed Lepidium, previously included within L. oleraceum, is distinct from that species in a number of well marked morphological and DNA molecular characters. At first the scientists, though delighted with the clean DNA sequences obtained for L. obtusatum, were puzzled by the DNA result. However, upon closer inspection the results make morphological sense. Both L. obtusatum and the unnamed Lepidium have a creeping habit, crenate leaves, and while the unnamed plant always has two stamens, and L. obtusatum normally four (like L. oleraceum), many specimens of L. obtusatum have between 2 and four stamens.
Further research into the relationship is intended using DNA sequences obtained from the chloroplast region.
A complete taxonomic revision of the L. oleraceum complex is due for completion within the next year.