Drosera occidentalis — Vorstman's Guide to the Carnivorous Plants

Identification

A tiny pygmy sundew up to 2.5 cm tall, with leaf blades sometimes only 1 mm across. At the heart of the rosette, as in all pygmy sundews, stands a tuft of stipules. The flowers are white or pink and appear in late spring and early summer, later than in most other pygmy sundews. The extremely small size, combined with a wet habitat on the coastal plain, is the best field character.

Similar species

Because of its tiny dimensions the species can only be confused with other very small pygmy sundews, such as Drosera oreopodion, which grows in the foothills of the Darling Range, and D. pygmaea. The habitat in coastal-plain wetlands and the late flowering are clues; a secure identification needs a hand lens and the key in Lowrie (2013).

The trap and how it works

An active flypaper trap on the smallest conceivable scale. Each millimetre-wide blade carries a few stalked glands with a sticky droplet. The prey is correspondingly small: springtails, mites and other micro-arthropods crawling over the wet ground. After a catch the tentacles bend towards the prey and it is digested.

Habitat and ecology

Wetlands of the coastal plain: the margins of seasonal swamps and wet, sandy hollows (W7, W4, D1). Because the ground there stays moist until late in spring, the plant can flower late. In summer it withdraws to a resting bud within the stipules.

Distribution and elevation

Endemic to south-west Australia, in wetlands from just north of Perth to just south of Busselton: the Swan Coastal Plain.

Recorded (one-degree cells)

Distribution based solely on records at GBIF (Global Biodiversity Information Facility), not on TDWG regions — those are often far larger than the actual range. The light halo is the area around a record, the dark core the record itself. The darker cells are 16 one-degree squares — roughly a hundred and ten kilometres — in which the species has been recorded, from all GBIF records. This is coarser than for most species because hardly any record of this plant carries an accurate coordinate: the locality of poached species is obscured at source. At this scale that obscuring disappears into the noise. The cells show where it has been seen, not where it occurs: an empty square means nothing.

Forms and variation

Besides the typical form the literature mentions a southern subspecies, D. occidentalis subsp. australis; we could not check its differences or current status in a source. Like most pygmy sundews the plant forms gemmae that are dispersed by raindrops.

Where and when to see it

Search in November and December, on your knees, along the edges of swamps on the coastal plain south of Perth. A plant 2.5 cm tall with millimetre-sized leaves is found only with patience; the best sign is a glint of tiny droplets on wet ground. A hand lens is indispensable.

Conservation status

On the global IUCN Red List the species is listed as Least Concern (LC). It is not listed in CITES. The coastal-plain wetlands between Perth and Busselton, however, have largely disappeared through drainage, agriculture and urbanisation, and the falling water table in the region is a lasting threat. Uncertainty: we could not check the status of subsp. australis.

Scientific name

Drosera occidentalis | Morren, 1912

Drosera occidentalis was described in 1912 by Alexander Morrison, in Journal of Botany, British and Foreign, volume 50, p. 166. The species occurs in wetlands of Western Australia, from just north of Perth to just south of Busselton. The precise type locality, collector and collection date of the original (1912) type material could not be established with certainty. The name is descriptive Latin: "occidentalis" means "western", referring to the species' distribution in southwestern Western Australia.

World Checklist of Vascular Plants (WCVP), via Plants of the World Online (POWO), Royal Botanic Gardens, Kew.