Drosera sewelliae — Vorstman's Guide to the Carnivorous Plants

Identification

A pygmy sundew with the build typical of the group: a small rosette of stalked round blades with tentacles around a bud of stipules, from which a slender inflorescence rises. Flower colour, flowering time and leaf and flower measurements are not given in the sources consulted; all measurement fields are therefore left empty. For a reliable description, Diels's original description (1904) and Lowrie's handbook (2013) are the sources to consult.

Similar species

Without published characters, no reliable distinction from related pygmy sundews can be given here. In the field a lens and an up-to-date key, such as that in Lowrie (2013), are essential; in pygmy sundews generally, look at the shape and colour of the stipule bud, the hairiness of the scape and the shape of the stigmas.

The trap and how it works

An active flypaper trap in miniature. Each leaf blade, often no larger than a pinhead to a few millimetres, carries stalked glands on its margin and upper surface, each holding a glistening sticky droplet; the marginal tentacles are usually the longest. A small animal that touches the droplets sticks fast, after which the tentacles bend towards the centre of the blade and press the prey against the digestive glands. The glands secrete enzymes and absorb nitrogen, phosphorus and minerals from whatever dissolves. Given the scale, the catch consists of the very smallest: springtails, mites, aphids, thrips and minute midges moving over or just above the sandy ground.

Habitat and ecology

Further habitat details are not given in the sources consulted. The codes assigned — sand and open heath (D1, B5) — reflect the most common setting of south-west Australian pygmy sundews and are a provisional estimate, not a published observation.

Distribution and elevation

Endemic to south-west Australia. No closer delimitation of the range was found in accessible sources. Altitudinal limits are not published.

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

Described by Ludwig Diels in 1904. The species is placed in section Lamprolepis, the pygmy sundews. No subspecies or varieties are recognised. Like nearly all pygmy sundews it probably forms gemmae, but this is not specifically recorded for this species in the sources consulted.

Where and when to see it

Without reliable data on flowering time and sites, targeted searching is difficult. Before a visit, consult FloraBase or a local plant society. For all pygmy sundews, the best chance is a sunny morning in late winter or spring, on your knees in open sand between the shrubs — and above all not standing on it.

Conservation status

Assessed as Least Concern (LC) on the IUCN Red List; not listed in CITES. Further data on populations or threats were not found in the sources consulted.

Scientific name

Drosera sewelliae | Diels, 1904

Drosera sewelliae was described in 1904 by Ludwig Diels, published in Botanische Jahrbücher für Systematik, volume 35: 206. The species occurs naturally only in a very small area in the far southwest of Western Australia; the only known population is near Chittering Valley. The material was collected by a "Miss Sewell". The exact type locality and date of collection could not be established with certainty. This is an eponym: Diels named the species after "Miss Sewell", the collector of the plant. Even in Diels' original description her first name is not given, and it could not be established with certainty.

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