(C.B.Clarke) D.J. Middleton & Mich. Müller
Description
Henckelia calva (C.B.Clarke) D.J.Middleton & Mich.Müller is a perennial herb of the Gesneriaceae (the input subtribe name Didymocarpinae notwithstanding), distributed across the eastern Himalaya and adjacent ranges. GBIF (a sparse 12 occurrences) records it from northern India, Bhutan and Myanmar, where it grows on shaded, moss-covered rocks, damp banks and forest understorey in humid broad-leaved and evergreen forest. The two Sikkim records at Yoksam, at 1,800 m and 2,750 m, both in August during the monsoon, indicate a montane preference broadly between 1,500 and 3,000 m, where high atmospheric humidity supports its growth.
The plant is a soft, more or less rhizomatous herb. Leaves are opposite, ovate to elliptic, often somewhat fleshy, with a crenate to serrate margin and a relatively sparse indumentum (the epithet "calva", meaning bald or glabrescent, alludes to this comparatively smooth surface). The inflorescences are axillary cymes bearing showy zygomorphic flowers; the corolla is tubular and bilabiate, white to pale violet or bluish, the throat sometimes marked with yellow. There are two fertile stamens with cohering anthers, and the ovary is superior, maturing into the elongate, narrowly cylindrical, twisted capsule characteristic of Henckelia, which splits to release numerous minute seeds.
The species was transferred from Didymocarpus to a recircumscribed Henckelia following molecular phylogenetic studies of Old World Gesneriaceae by Middleton, Möller and collaborators, a reclassification that reshaped generic limits in the subtribe Didymocarpinae. As a narrow-range, hygrophilous understorey herb of the eastern Himalaya, it is intrinsically vulnerable to forest disturbance and habitat loss, and its few documented occurrences underline the need for continued field survey of the region's Gesneriaceae.
Author: (C.B.Clarke) D.J. Middleton & Mich. Müller · Sources: POWO (Kew), Flora of Bhutan Vol. 2, Flora of China Vol. 18, GBIF, Weber & Burtt: Remarks on the classification of Gesneriaceae