Hairy Mulla Mulla

Ptilotus helipteroides
Habit of Ptilotus helipteroides. Photo by T. Hammer.

Ptilotus helipteroides (F.Muell.) F.Muell., commonly called ‘hairy mulla mulla’, was described by Ferdinand von Mueller in Fragmenta Phytographiae Australiae (1862) as Trichinium helipteroides F.Muell. The type specimen was collected from near Nichol Bay, present-day Karratha, Western Australia. It is a widespread small herb with papery pink flowers, that can be seen to flower en masse in many of the drier parts of Western Australia and central Australia. The specific epithet refers to its similarity with the paper daisy genus Helipterum DC. (Asteraceae), which can also have papery pink flowers and can form large stands of flowering displays. Many of the species of Helipterum have be transferred to other genera (e.g. Rhodanthe Lindl.). This choice of a specific epithet is perhaps unfortunate, as I do not think that the two plants share a close affinity.

I suppose that the common name ‘hairy mulla mulla’ probably refers to the hairs that cover the leaves and stems of the species, apart from other ‘mulla mulla’ species (like Ptilotus exaltatus Nees, ‘tall mulla mulla’), which tend to be glabrous on the stem and leaves. Since many Ptilotus spp. have a persistent indumentum on the vegetative surface, I think this common name can potentially lead to confusion, as common names tend to do.

Ptilotus helipteroides
An open flower of Ptilotus helipteroides. Photo by T. Hammer.

Ptilotus helipteroides has an interesting floral morphology. It has 4 fertile stamens opposite to the lower sepals (or ‘tepals’) and one staminode opposite the upper sepal. This staminode is coloured orange at its base, and it is flanked by two staminal cup appendages that are also coloured orange and decorated with coloured fringed hairs. Smaller, uncoloured staminal cup appendages alternate with the stamens.  These features no doubt serve as signals for pollinators to land in a specific orientation, probably with insects’ head orientated towards to the staminode and probing the staminal cup for nectar. The stamens are curved and orientated to place the pollen on the under section of the pollinator. The flowers appear to be protandrous. A similar pollination mechanism has been observed in Ptilotus gaudichaudii (Steud.) J.M.Black, though the arrangement of the stamens in relation to the style and colours of the flowers varies between these species (Hammer et al., 2018). The P. gaudichaudii species group (also including P. modestus T.Hammer and P. eremita (S.Moore) T.Hammer & R.W.Davis) has been found to be closely related to P. helipteroides on recent molecular phylogenies of the genus (e.g. Hammer et al., 2015). Also closely related to P. helipteroides is P. pseudohelipteroides Benl.

– Hammer, T., Davis, R. & Thiele, K. (2015). A molecular framework phylogeny for Ptilotus (Amaranthaceae): Evidence for the rapid diversification of an arid Australian genus. Taxon 64(2): 272–285.
– 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.
– Mueller, F.J.H von (1862). Fragmenta Phytographiae Australiae. Vol. 3. (Government Printer: Melbourne)