In my recent paper (Hammer et al., 2018), two species were reinstated from Ptilotus gaudichaudii (Steud.) J.M.Black (Amaranthaceae), Ptilotus eremita (S.Moore) T.Hammer & R.W.Davis and Ptilotus modestus T.Hammer. These species were previously included as subspecies under P. gaudichaudii, namely subspp. parviflorus (Benth.) Lally and eremita (S.Moore) Lally. The paper includes the taxonomic and nomenclatural histories of the species, including the justification for raising them to species rank.
This study was spurred by observations made in the field, particularly the species P. eremita and P. gaudichaudii, which overlap significantly in their distributions and were found co-occurring at several sites without any intermediates. The species boundaries within this group was assessed by examining the morphology of specimens from throughout their ranges.
Ptilotus gaudichaudii can be reliably discriminated from the other two species by having larger tepals (technically sepals), style, staminal filaments and anthers and having widely-gaping showy flowers (Fig. 1). Ptilotus eremita by comparison has flowers which do not gape widely after anthesis, and instead form a tube down to to the ovary (Fig. 2). The small stamens crowd the pistil and do not orientate themselves in the way observed for P. gaudichaudii. Ptilotus modestus is most similar to P. eremita, but the latter varies from the former by having a slightly longer style and staminal filaments and having three fertile stamens (as opposed to four) and occurring in central and eastern Australia (as opposed to Western Australia). Read more about this study here: http://www.publish.csiro.au/sb/SB17026.
Hammer, T.A., Davis, R.W. & Thiele, K.R. (2018). The showy and the shy: reinstatement of two species from Ptilotus gaudichaudii (Amaranthaceae). Australian Systematic Botany 31: 1–7. https://doi.org/10.1071/SB17026