Stachystemon exilis (Euphorbiaceae), a new and potentially threatened species from the Swan Coastal Plain

The small, endemic Western Australian genus Stachystemon Planch. (Euphorbiaceae: Caletieae: Pseudanthinae) was last revised by Halford and Henderson (2003) at which time nine species were recognised. Stachystemon exilis Hislop & R.W.Davis, a new and uncommon species from the Swan Coastal Plain described below, is the first to be published since that treatment. Although the earliest collections of this species were made before the revision was completed, it appears that its authors had no opportunity to examine this material during the course of their studies.