Notes. Rhodanthe manglesii and R. cryptantha normally occur in pure stands in native vegetation throughout their ranges. However, during floristic surveys of the Wheatbelt Woodlands Threatened Ecological Community for the Wheatbelt Natural Resource Management Group, they were found in sympatry in several relatively undisturbed sites. The distinctiveness of the two species at such sites is illustrated in Figs 1 & 2, showing plants from a co-occurring, co-flowering natural population of both species. The plants considered as R. manglesii at this site closely match the illustration in Lindley (1834). Over several years of observations on floristic quadrats established at this site, no sign of intermediates have been detected, indicating that the populations comprise separate species.

By contrast with R. cryptantha, R. manglesii plants are usually larger (15–40 cm tall), with (1–)3–5(–7) inflorescences per plant borne on several (5–6) stem divisions and has larger basal leaves (20–37 mm long and 10–15 mm wide). There are usually more flowers per inflorescence (30–55), and the inflorescences are campanulate and (15–)20–35 mm wide at anthesis, with silver to brilliant white basal inflorescence bracts. The terminal inflorescence bracts (without claw) are (10–)12–15 mm long and are bright pink and highly visible. Basal inflorescence bracts (without claw) are 8–10 mm long.

Although considerable variation occurs in the size of these annual plants depending on seasonal and site conditions, mature plants of R. cryptantha are normally smaller in all dimensions (height, leaf size, bract size) than R. manglesii. The inflorescence characters are the most readily observable differences between the species in the field.

Because of the tubular nature of the mature inflorescences of R. cryptantha, only 3–5 mm of the terminal pink bracts are visible at flowering beyond the dull white lower bracts, making the plants much less visible from a distance than R. manglesii. In that species, the large bright pink terminal inflorescence bracts are well-displayed beyond the lower silver-white bracts in the campanulate inflorescence. All inflorescence bracts in R. cryptantha are smaller than those of typical R. manglesii. The combination of size, colour and shape of the inflorescences, fewer inflorescences per plant, and smaller stature means that R. cryptantha is less showy in the field than R. manglesii. It appears from qualitative field observations that R. cryptantha receives far fewer visits by native bees than R. manglesii, suggesting that it may be at least partially inbreeding.

The inflorescences open at seed maturity to release the fruits, making the shape more like that of R. manglesii at this stage, but the other diagnostic differences remain.

Distribution. Rhodanthe cryptantha is largely confined to the Western Australian Agricultural Zone, between Geraldton and Ravensthorpe. Flowering occurs between August and October. The species is considered widespread and well-conserved.

Etymology. The specific name derives from the Greek meaning hidden flowers.

Typification: The BM collection states "Mount Brown, York, W.A. OH Sargent 1404" (photo!). A MEL collection (019635!) labelled "Mt. Brown, York, Sargent 1404, a, 8/9/1922" is a syntype. This collection is labelled in Sargent’s hand as Helipterum cryptanthemum and as Sargent 1404, a; probably indicating it was regarded as part of the same gathering as Sargent 1404.

The PERTH collection (0570295!) labelled as a type states "‘Cut Hill, York’, Sargent 1404, 28/9/1922". There is also a collection at MEL (0109636A!) from there labelled as "Sargent s.n., 2/9/1923". The last is probably not a type and the former could be a type but the collection site is a different locality.

Rhodanthe manglesii is illustrated in colour by Sarah Drake from material grown by Robert Mangles in 1833. The illustration, which accompanies the description of the species by John Lindley (Lindley 1834), is used in this study as indicative of the morphology of plants corresponding to this species.