Drosera arachnoides — Vorstman's Guide to the Carnivorous Plants

No photograph of this species under a Creative Commons licence or in the public domain is in the guide yet.

Identification

A small plant 2.5 to 6 cm tall, which in mature specimens forms a short stem 25 to 45 mm long. The leaves are long and thin, 22 to 40 mm long, and hairy, with glandular tentacles along the trapping blade; together they give the plant its spidery look. Data on flower colour and flowering time were not available in the sources consulted; those fields are left empty.

Similar species

Its closest relative is Drosera humbertii, also endemic to Madagascar but from higher mountain areas in the north. The two thus differ in habitat, altitude and range, besides morphological details. Drosera madagascariensis forms a longer stem with long-petioled leaves and grows in marshy grassland, not on rock faces in rainforest.

The trap and how it works

An active flypaper trap, as in all sundews. The long leaves project from the rock face and catch small insects flying in the humid air along the waterfall; after contact tentacles bend towards the prey and digestive enzymes are secreted.

Habitat and ecology

Moist rock surfaces along waterfalls in tropical lowland rainforest, partly in half shade (R1, B3). Photographs in the original publication also show plants on red clayey soil among tall sedges.

Distribution and elevation

Endemic to Madagascar, in the east of the island (Toamasina and Fianarantsoa provinces). Given the sensitivity of the species this guide gives no more precise localities. The authors expect more populations to be found in the poorly explored eastern rainforest. Altitudinal limits are not recorded; it is a lowland plant.

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 2 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. The species was described from collections made in 2010 and 2016 by Malagasy botanists and placed phylogenetically next to D. humbertii in section Ptycnostigma. (English Wikipedia places it in section Drosera; the original publication takes precedence.)

Where and when to see it

The known population lies in a protected area; visit only with a permit and a local guide. Pick or collect nothing, and do not share exact locations.

Conservation status

Not assessed for the global IUCN Red List (NE) and not listed in CITES. In the original publication the authors propose a provisional IUCN category of Vulnerable; a press release speaks of 'endangered'. Fewer than 1000 plants are known in the wild. Deforestation of the eastern lowland rainforest is the main threat.

Scientific name

Drosera arachnoides | Rakotoarivelo & Fleischmann, 2020

Described by Fleischmann, Rakotoarivelo, Roccia, Gonella, Andriamiarisola, Razanatsima & Rakotoarivony, published 8 July 2020, in Plant Ecology and Evolution, volume 153, no. 2, p. 284, figs. 1-4 — one of the most recently described species in the entire guide. Fianarantsoa and Toamasina provinces, Madagascar; the exact site and elevation could not be established. Herbarium specimens deposited at TAN, MO and P. From the Greek/Latin arachnoides ("spider-like", from arachne, "spider") — probably referring to a web-like or radiating arrangement of the leaves or tentacles, though this is not literally confirmed in a source.

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