Nowhere to be seen: Deyeuxia abscondita (Poaceae), a new but presumed extinct species from south-western Australia

On 8th December 1877 Ferdinand von Mueller travelled from Bunbury to the Balingup area of Western Australia during a survey for a report on the forest resources for the government (Mueller 1879). A grass collected that day from ‘Preston River’ (Figure 1) or ‘Blackwood and Preston Rivers’, as stated on two different handwritten labels, lay unidentified even to genus for more than a hundred years until assigned to Deyeuxia Clarion ex P.Beauv. by N. Walsh in 1987. A second specimen remained unidentified for a further period until tentatively suggested to be Lachnagrostis Trin. by A.J. Brown in 2002 or Dichelachne Endl. by Walsh and Brown in 2003. When I was consulted as to whether the plant was known or a placement could be suggested, I could not recognise it and was unable to find a match in the collections at the Western Australian Herbarium (PERTH), but considered that Pentapogon R.Br. was another possible genus placement. Upon further, more detailed examination of its spikelets, I have concluded that it does indeed belong in Deyeuxia. Field work has so far failed to discover any live plants so it must be presumed to be extinct. It is formally described here to draw it to the attention of people who might look for it, enable its recognition if rediscovered, and to place on record the characteristics of this lost element of biodiversity.