Drosera humbertii — 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 rosetted sundew with elongated glandular leaves, growing on wet rocks. A reliable description with measurements was not available for this text; the measurement fields are left empty.

Similar species

Drosera arachnoides is its closest relative: also a Malagasy rock dweller, but from the eastern lowlands, whereas D. humbertii grows higher up in the north. Drosera madagascariensis forms a stem and grows in marshy grassland; D. natalensis and D. burkeana are rosette species of wet open ground.

The trap and how it works

An active flypaper trap: sticky droplets on stalked glands hold small insects, after which the tentacles bend towards the prey and the glands secrete digestive enzymes.

Habitat and ecology

Moist rocks and rock faces in the mountains, partly within the cloud-forest zone, where seepage and mist keep the plant wet (R1, B4, R3). Specific habitat data are scarce.

Distribution and elevation

Endemic to Madagascar, in the mountains of the north of the island, at higher elevations than D. arachnoides. Precise altitudinal limits are not given in the sources consulted.

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 are recognised. According to Rakotoarivelo and Fleischmann (2020) D. humbertii belongs with D. arachnoides to section Ptycnostigma.

Where and when to see it

The sites lie in remote mountain areas, often in national parks where a permit and guide are required. Search wet, vegetated rock faces.

Conservation status

Not assessed for the global IUCN Red List and not listed in CITES. The range is small and tied to mountain habitats; deforestation and fires around the mountains of northern Madagascar are a general threat.

Scientific name

Drosera humbertii | Exell & Laundon, 1956

Described by Exell & J.R. Laundon in 1956, in Boletim da Sociedade Broteriana, series 2, volume 30, p. 219. The precise type locality could not be established. The species occurs in Madagascar. Probably named after Henri Humbert (1887-1967), the leading French authority on the Madagascar flora of that era — a strong inference given the context, but not literally confirmed in a source.

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