Royal mulla mulla

Royal mulla mulla
Ptilotus rotundifolius near Tom Price in the Pilbara, Western Australia. Photo by T. Hammer.

One of my favorite species is Ptilotus rotundifolius (F.Muell.) F.Muell, the royal mulla mulla, which is found in the Pilbara, Gascoyne and Murchison bioregions of Western Australia. This long-lived shrub can reach > 2 m high. The specific epithet (rotundifolius) refers to the large and broad leaves (> 3 cm wide), which are covered in the a dense, velvety indumentum. These leaves make it one of the most cuddly Ptilotus species. The species was originally described by Mueller (1862) in the genus Trichinium, which was later included within Ptilotus by Mueller (1868).

Ptilotus rotundifolius
Ptilotus rotundifolius on a hill with exposed banded iron formation rocks near Cue, Western Australia. Photo by T. Hammer.

Ptilotus rotundifolius is closely related to P. marduguru Benl (Benl, 1980; Hammer et al., 2015), a rare species from Southesk Tablelands in the Great Sandy Desert, Western Australia. These two species do not overlap in distribution and can be easily differentiated based on P. rotundifolius having pink flowers and spiciform inflorescences > 30 mm wide. Ptilotus marduguru has cream-green flowers and inflorescences that are < 21 mm wide. Like P. marduguru and other closely related species (e.g. P. auriculifolius (A.Cunn. ex Moq.) F.Muell.), P. rotundifolius has 5 fertile stamens and a centrally placed style on the ovary. These characters were found to be associated with the basal clades of Ptilotus (Hammer et al., 2015) and are probably pleisiomorphic within the genus.

Ptilotus rotundifolius
An open flower of Ptilotus rotundifolius (F.Muell.) F.Muell. Photo by T. Hammer

The pink flowers and densely wooly indumentum on the interior surface of the sepals (sometimes “tepals”) of P. rotundifolius are shared with more distantly related species such as P. drummondii (Moq.) F.Muell., P. exaltatus Nees and Ptilotus manglesii (Lindl.) F.Muell., all of which have been observed to be pollinated by native Australian bees (pers. obs.). These characters may be indicative of a bee pollination syndrome in the genus. The close relatives to P. rotundifolius that have green flowers (i.e. P. marduguru and P. auriculifolius) may be pollinated by moths like more distantly related green-flowering species, such as P. macrocephalus (R.Br.) Poir. and P. polystachyus (Gaudich.) F.Muell. (pers. obs.). Shifts in pollination syndromes from bees to moths (or vice versa) may be an important driver of speciation throughout the genus.

  • Benl, G. (1980). Five new taxa of Ptilotus (Amaranthaceae) from Western Australia. Nuytsia 3: 157-161.
  • 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.
  • Mueller, F.J.H von (1862). Fragmenta Phytographiae Australiae. Vol. 3, p. 122. (Government Printer: Melbourne)
  • Mueller, F.J.H von (1868). Fragmenta Phytographiae Australiae. Vol. 6, p. 230. (Government Printer: Melbourne)

Pom poms

Ptilotus manglesii habit
The habit of Ptilotus manglesii near Bindoon in Western Australia. Photo by T. Hammer.

Ptilotus manglesii (Lindl.) F.Muell. (commonly called mulla mulla or pom poms) is a perennial herb endemic to the south-west of Western Australia and common in the hills around Perth, typically occurring in Eucalyptus woodlands and forests. It was described as Trichinium manglesii by John Lindley in Edwards’ botanical register in 1839 from “Swan River Colony” (probably near present-day Perth). It was later transferred to Ptilotus R.Br. by Mueller (1868). The species was named for Captain James Mangles of the Royal Navy, who was interested in botany and horticulture in colonial Western Australia and had collected plant specimens for Lindley.

Ptilotus manglesii
An inflorescence of Ptilotus manglesii (Lindl.) F.Muell. Photo by T. Hammer

Ptilotus manglesii has been found to be closely related to P. nobilisP. exaltatus species group on the molecular phylogeny of the genus (Hammer et al., 2015). Ptilotus exaltatus overlaps slightly in distribution with P. manglesii around Geraldton, Western Australia. It can be easily distinguished from P. exaltatus by its perennial, decumbent habit, as well as multiple floral characters. Two phrase-names at the Western Australian Herbarium, Ptilotus sp. Beaufort River (G.J. Keighery 16554) and Ptilotus sp. Porongurup (R. Davis 10805), that are morphologically similar to P. manglesii are currently being investigated as putative new species. More to come about these two!

  • 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.
  • Mueller, F.J.H von (1868). Fragmenta Phytographiae Australiae. Vol. 6, p. 230. (Government Printer: Melbourne)

The showy and the shy

Ptilotus gaudichaudii
Fig. 1. An inflorescence of Ptilotus gaudichaudii, showing open flowers. Photo by T. Hammer.

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 eremita
Fig. 2. An inflorescence of Ptilotus eremita, showing an open flower (centre). Photo by T. Hammer.

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:

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.

Ptilotus benlii

Ptilotus benlii
Flowering inflorescences of Ptilotus benlii. Photo by R. Davis.

Ptilotus benlii R.W.Davis & T.Hammer was recently described in the journal Nuytsia as a new species for Western Australia (Davis & Hammer, 2017). It is a perennial herb found from south of Kalbarri to north of Merridin, WA.

Ptilotus benlii is closely related to P. calostachyus F.Muell., P. drummondii (Moq.) F.Muell., P. aphyllus Benl and P. schwartzii (F.Muell.) Tate. It shares the character with these species of possessing staminal cup appendages, but can be easily differentiated by its larger, green-white flowering spikes and bright pink filaments and stamens. Ptilotus benlii is also quite close to the southwestern species P. esquamatus (Benth.) F.Muell., with which it differs in that the latter lacks staminal cup appendages and has much smaller inflorescences of pinkish flowers and a decumbent habit.

Ptilotus benlii
The habit of Ptilotus benlii. Photo by R. Davis.

The species was named in honour of German botanist Gerhard Benl (1910–2001), who contributed significantly to the taxonomy of Ptilotus throughout his career, naming upwards of 30 species and various infraspecific taxa.

Davis, R.W. & Hammer, T.A. (2017). Ptilotus benlii (Amaranthaceae), a new species from Western Australia. Nuytsia 28: 299–302.