Drosera orbiculata — Vorstman's Guide to the Carnivorous Plants

Identification

A perennial with an underground tuber and a flat rosette about 1.5 cm across, far smaller than well-known rosette-forming tuberous sundews such as Drosera erythrorhiza. The leaf blades are round, which gave the species its name. We did not find flower colour, flowering time or further measurements in any source consulted; those fields are left empty.

Similar species

The species is regarded as related to Drosera rosulata, another small rosette-forming tuberous sundew from the south-west. Other members of section Erythrorhiza, such as D. macrophylla, D. erythrorhiza and D. lowriei, are larger or have a different leaf shape. A small rosette with round blades in a wet hollow north of Perth is the best clue.

The trap and how it works

An active flypaper trap. The upper surface of the flat-lying round leaves carries stalked glands with sticky droplets that catch crawling and low-flying insects such as ants, springtails and small flies. After a catch the tentacles bend towards the prey and digestive enzymes are secreted. The reserves go to the tuber, which is formed anew each year.

Habitat and ecology

Sandy clay in hollows and drainage washes that are wet in winter (W7, D1). The plant grows in the wet winter, flowers and withdraws into its tuber in the dry summer.

Distribution and elevation

Endemic to south-west Australia, known from a very small area north of Perth, in the Gillingarra district.

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 square is the only one-degree cell — 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. It shows where the species has been seen, not where it occurs: an empty square means nothing.

Forms and variation

No subspecies or varieties have been described. The species belongs to section Erythrorhiza, the rosette-forming tuberous sundews, within subgenus Ergaleium.

Where and when to see it

Rosette-forming tuberous sundews are above ground in winter, roughly from June to September. A rosette a centimetre and a half across in a wet hollow is found only by searching the ground systematically. Because the range is so small: look, photograph, and leave the site undisturbed.

Conservation status

On the global IUCN Red List the species is listed as Vulnerable (VU). It is not listed in CITES. So small a range makes the species sensitive to any change: clearing, alterations to the drainage of hollows and roadworks. Uncertainty: we could not check flower colour, flowering time or the Western Australian conservation status in a source.

Scientific name

Drosera orbiculata | Marchant & Lowrie, 1992

Drosera orbiculata was formally described in 1992 by Neville Marchant and Allen Lowrie, in Kew Bulletin, volume 47, issue 2, page 319. The type was collected by Allen Lowrie on 10 June 1986 in the Victoria Plains district of Western Australia, near Gillingarra (about 1.3 km north of it), not far from Perth. The plant grew there on sandy clay soil in winter-wet depressions and washes. The type specimen is held at the PERTH herbarium (PERTH 2344963). The epithet orbiculata comes from the Latin orbiculatus, "rounded, disc-shaped." It is a descriptive name: the species was so named for the nearly circular shape of its leaf blade.

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