Ridleyandra species are perennial herbs. The stems are often woody, and may be short or elongate, and often hairy. Leaves are usually held in a dense rosette or loose tuft on top of the stem. The species are distributed through the Malay Peninsula and Borneo, in lowland and (more frequently) montane rain forests.
The genus is one of the groups separated from Didissandra. It can be divided into two morpho-geographical groups:
(a) sect. Ridleyandra (approx. 18 spp., corolla with long tube, nectary present; Malay Peninsula, and
(b) sect. Stilpnothrix (C.B.Clarke) A.Weber & B.L.Burtt (5 spp., Borneo; corolla short-tubed to flat-faced, nectary lacking).
The Bornean species show a gradual acquisition of the pollination syndrome of oligandric pollen flowers. Evidence that the two groups are properly within the same genus is provided by the characteristic seed coat structure (testa cells with longitudinal ridge in the middle).
Ridleyandra species can be very dramatic and attractive plants, although cultivation may be difficult.
Source (adapted): Genera of Gesneriaceae