New Ptilotus species from the Gascoyne

A new species of Ptilotus (Amaranthaceae) has been described in Volume 29 of Nuytsia. The new species, Ptilotus yapukaratja R.W.Davis & T.Hammer, is a shrub with succulent leaves and pink flowers (pictured) that occurs near Lorna Glen Station (Matuwa) in the Gascoyne bioregion of Western Australia. The specific epithet was proposed by the Elders from the Tarlka Matuwa Piarku Aboriginal Corporation, the traditional custodians of the Matuwa Kurrara Kurrara Indigenous Protected Area and is derived from their words yapu (rock) and karatja (belonging to), referring to the rocky habitat on which it is found. The species is rare and listed as Priority One under Conservation Codes for Western Australian Flora. Further information can be found in the publication:

Davis, R.W. & Hammer, T.A. (2018) Ptilotus yapukaratja (Amaranthaceae), a new and rare species from the Gascoyne bioregion of Western Australia. Nuytsia 29: 157–160. [pdf]

Gynodioecy and Ptilotus obovatus

Ptilotus obovatus
The habit of Ptilotus obovatus in the Gascoyne bioregion, Western Australia. Photo by T. Hammer.

Within the genus Ptilotus R.Br. (Amaranthaceae), one of the most common, yet enigmatic, species is the shrub Ptilotus obovatus (Gaudich.) F.Muell., sometimes referred to as ‘silver mulla mulla’ or ‘cotton bush’. Charles Gaudichaud-Beaupré (1829) originally described the species based on a specimen from near Shark Bay, Western Australia as Trichinium obovatum Gaudich. The species was later transferred to Ptilotus by Ferdinand von Mueller (1868). The species is widespread throughout the arid interior of Australia, and it is morphologically diverse.

An interesting phenomenon within the species is the presence gynodioecy, which is a dimorphic sexual system consisting of both hermaphrodite (i.e. having a functional androecium and a gynoecium) and female individuals (i.e. laking a functional androecium) in a population (Stewart & Barlow 1976). Within P. obovatus, the hermaphrodite individuals have three stamens and two yellow, appendage-like staminodes. The female individuals lack functional stamens, which instead take on the appearance of the staminodes in the hermaphrodite individuals and effectively having five staminodes instead of regularly two (see below images). Some populations have a majority of female individuals (pers. obs.).

Stewart and Barlow (1976) looked at polyploidy and a number of interesting features found in P. obovatus, including gynodioecy. Of the five localities counted for male sterility by Stewart and Barlow (1976) in WA and SA, four of the localities had more female individuals than hermaphrodites. The cytological samples examined found a lower sex ratio than field samples, in part because a number of plants that appeared to be hermaphrodite had anthers that did not produce pollen. Field observations of male-sterile plants could be underestimating them within the population, as it is difficult to determine in the field if plants are functionally hermaphrodite. Additionally, Stewart and Barlow (1976) attempted to look at self-compatibility within P. obovatus, but were unable to produce experimental crosses, which they “attributed to technical problems related to floral structure” (p. 244). They presumed that diploid P. obovatus was self-compatible due to the successful setting of two seeds from one plant. A study of self-compatibility within Ptilotus is warranted.

Ptilotus obovatus is not the only species within Ptilotus to possess gynodioecy. Ptilotus schwartzii (F.Muell.) Tate is another widespread arid species with gynodioecy (see images below), some populations having female individuals far outnumbering hermaphrodite individuals (pers. obs.). One species, P. crispus Benl, is known to be dioecious (i.e. separate male and female individuals in a population), and close relatives of Ptilotus also have dioecy (e.g. Aerva Forssk.).

Since Darwin, there has been much speculation as to why we find gynodioecious species. He perhaps did much to shape the view of gynodioecy shared by subsequent authors, that is a mid-way point between hermaphroditism and dioecy. Yet Darwin (1877) saw difficulty in seeing the need for this shift in sexuality, remarking (pp. 279–280):

There is much difficulty in understanding why hermaphrodite plants should ever have been rendered dioecious. There would be no such conversion, unless pollen was already carried regularly by insects or by the wind from one individual to the other; for otherwise every step towards dioeciousness would lead towards sterility. As we must assume that cross-fertilisation was assured before an hermaphrodite could be changed into a dioecious plant, we may conclude that the conversion has not been effected for the sake of gaining the great benefits which follow from cross-fertilisation. We can, however, see that if a species were subjected to unfavourable conditions from severe competition with other plants, or from any other cause, the production of the male and female elements and the maturation of the ovules by the same individual, might prove too great a strain on its powers, and the separation of the sexes would then be highly beneficial. This, however, would be effected only under the contingency of a reduced number of seeds, produced by the females alone, being sufficient to keep up the stock.

Darwin (1877) concluded by saying that the females of a gynodioecious species produce more seeds than if they were hermaphrodites (p. 345), thus justifying decreased pollen production.

  • Darwin, C. (1877). The different forms of flowers on plants of the same species. (John Murray: London)
  • Gaudichaud-Beaupré, C. (1829). Voyage Autour du Monde … sur les Corvettes de S.M. l’Uranie et la Physicienne. Botanique 11: 445.
  • Mueller, F.J.H. von (1868). Fragmenta Phytographiae Australiae 6(49): 228.
  • Stewart, D.A. & Barlow, B.A. (1976). Infraspecific polyploidy and gynodioecism in Ptilotus obovatus (Amaranthaceae). Australian Journal of Botany 24: 237–248.

Ptilotus actinocladus

Ptilotus actinocladus
The new species, Ptilotus actinocladus T.Hammer & R.W.Davis. Photo by G. Byne.

A new and rare species, Ptilotus actinocladus T.Hammer & R.W.Davis, has been recently published in volume 29 of the journal Nuytsia (Hammer & Davis, 2018). The new species is endemic to the Gascoyne bioregion of Western Australia and known from several collections, mostly around Doolgunna Station.

Ptilotus pseudohelipteroides
Ptilotus pseudohelipteroides Benl in South Australia. Photo by T. Hammer.

Specimens currently within P. actinocladus were previously assigned to P. pseudohelipteroides Benl, constituting the only specimens of this species from Western Australia. The type of P. pseudohelipteroides is from Queensland, with the typical variety of this species occurring in the Northern Territory, Queensland and South Australia. Ptilotus pseudohelipteroides was described by Gerhard Benl (1959), based on the variety Trichinium helipteroides F.Muell. var. minor J.M.Black described by John M. Black (1924) and latter the combination made within Ptilotus by Hansjörg Eichler (as P. helipteroides var. minor). Benl separated P. pseudohelipteroides from P. helipteroides (F.Muell.) F.Muell. based on it varying in floral and vegetative characters.

Ptilotus actinocladus map
Map the distribution of Ptilotus actinocladus (triangles), P. helipteroides (vertical shading) and P. pseudohelipteroides (horizontal shading).

When examining the specimens from Western Australia for the identification key to the Ptilotus (available on KeyBase), it was clear that these were different from P. pseudohelipteroides. The morphological variation and geographical disjunction between the two entities clearly showed that the specimens from Western Australia deserve to be placed within its own species. The new species does overlap with P. helipteroides, but is also morhologically distinct from that species in multiple floral and vegetative characters, including the habit, leaf and stem indumentum, and size of the floral parts (which are more similar to P. pseudohelipteroides). The specific epithet of the new species refers to the radiating (actino-) stems (cladus) that are prostrate and characteristic of this species. Please feel free to read it in more detail on FloraBase, at

  • Benl, G. (1959). New species and varieties of Ptilotus R.Br. (Amaranthaceae). Muelleria 1(2): 105–107.
  • Black, J.M. (1924). Casuarinaceae – Euphorbiaceae. Flora of South Australia 2: 212.
  • Eichler, Hj. (1965). Supplement to J.M.Black’s Flora of South Australia (Second Edition, 1943-1957): 130.
  • Hammer, T.A. & Davis, R.W. (2018). Ptilotus actinocladus (Amaranthaceae), a new and rare species from the Gascoyne bioregion, Western Australia. Nuytsia 29: 145–149. (pdf)

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)

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.