Drosera caduca — Vorstman's Guide to the Carnivorous Plants

Identification

A perennial rosette plant of the D. petiolaris complex, often forming several rosettes at once from its root system so that small clusters arise. The juvenile leaves, as in its relatives, have a long stalk with a small trapping blade bearing glandular tentacles. In the adult leaves these tentacles are absent; the blade is then no longer sticky. This is the most reliable field character. The flowers are white. Reliable measurements were not available for this guide; the measurement fields are therefore left empty.

Similar species

Other species of the D. petiolaris complex in the Kimberley, such as D. petiolaris, D. derbyensis and D. dilatatopetiolaris, carry glandular tentacles on all leaves. An adult rosette without sticky blades is therefore already strong evidence for D. caduca within the group. Young plants with fully glandular juvenile leaves can hardly be told from relatives without locality data.

The trap and how it works

An active flypaper trap, but only in youth. The juvenile leaves carry glandular tentacles that, as in other sundews, catch and digest small insects in sticky mucilage. As the plant matures, the tentacles disappear from new leaves, and with them largely the carnivorous function. Why the plant does this has not been explained; perhaps in its habitat the saving from not producing glands outweighs the yield of the catch.

Habitat and ecology

White sandy soil along creek margins (D1), in places that are wet in the rainy season and dry out afterwards (W7), in a landscape of savanna and open woodland on sandstone (B6).

Distribution and elevation

Endemic to the northern Kimberley of Western Australia: from the Edkins Range to the southern part of Prince Regent National Park, and on Augustus Island. The range description 'tropical northern Australia' is therefore broader than the actual range, which is confined to Western Australia. Altitudinal limits are not published in the sources consulted; the elevation field is left empty.

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 3 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

No varieties are recognised. The species was described in 1996 by Allen Lowrie. The loss of tentacles on adult leaves is very unusual in the genus; it is therefore important to examine adult, not only young, leaves when identifying it.

Where and when to see it

The sites lie in one of the most remote parts of Australia and are mostly reachable only by boat, helicopter or long overland expeditions. Anyone who gets the chance should search in the late wet season along creeks with white sand for clusters of rosettes whose leaves do not glisten. The area is partly national park and partly Aboriginal land; access requires permission.

Conservation status

On the IUCN Red List the species is Least Concern (LC); it is not listed in CITES. The range is small but lies in one of the least disturbed parts of Australia, partly within Prince Regent National Park. Possible threats are changes in fire regime and feral grazing animals.

Scientific name

Drosera caduca | Lowrie, 1996

Described by Allen Lowrie in 1996, in Nuytsia, volume 11, no. 1, p. 55-69. August Island, Western Australia; type material collected on 27 May 1993. From the Latin caducus ("dropping off early") — refers to the absence of sticky trapping hairs on all but the youngest leaves: mature leaves lose their glandular traps.

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