Harry Sm.
Description
Saxifraga sherriffii is a narrowly endemic alpine cushion plant known only from Bhutan (BT), where it is represented by a mere handful of records, around six documented occurrences. It is confined to the high alpine and subnival zone, growing on exposed rock ledges, in crevices of cliffs and on stony, well-drained slopes near the limit of vascular plant life. The type material and the plant shown here come from Jule-Tso in Bhutan at 4400 m, flowering in June; the species commemorates the collector George Sherriff, who with Frank Ludlow explored the Bhutanese and southeastern Tibetan mountains, and its extreme rarity reflects both its restricted range and the inaccessibility of its habitat.
The plant forms a small, dense, tufted to cushion-like perennial of woody-based rosettes. The leaves are small, crowded, spathulate to oblong and somewhat fleshy or leathery, frequently bearing chalk-secreting hydathode pits along the margin in the manner of the encrusted saxifrages, and clothed with glandular hairs. The flowering stems are short and glandular-pubescent, carrying few flowers. Each flower has five spreading petals, white to pale yellow and sometimes spotted, set above a half-inferior ovary, with ten stamens; the calyx lobes are reflexed in fruit. The fruit is a two-beaked capsule dehiscing between the divergent styles to release numerous minute seeds.
Saxifraga is a large, predominantly arctic-alpine genus in which the Himalayan high mountains hold many localised endemics. S. sherriffii belongs to the cushion-forming, lime-encrusting assemblage adapted to cold, wind-exposed, nutrient-poor rock habitats, where the compact growth form conserves heat and moisture. Given its tiny known range, very small number of populations and specialised high-alpine niche, this Bhutanese endemic is of considerable conservation interest and potentially vulnerable to climate-driven contraction of suitable habitat.
Author: Harry Sm. · Sources: POWO (Kew), GBIF, Flora of Bhutan, Saxifragaceae of the Himalaya, Saxifraga (Webb & Gornall monograph)