Harry Sm.
Description
Saxifraga vacillans Harry Sm. is a high-alpine cushion- to mat-forming saxifrage of the eastern Himalaya, known from only a handful of georeferenced collections, all from Bhutan. It is a plant of the upper alpine zone, growing among rocks, on stabilised scree, in moist turf and in the crevices of cliffs and moraines well above the treeline. The single documented locality at Chele-La, photographed at 4,100 m in May, is characteristic of its narrow elevational preference for sites between about 3,800 and 4,500 m, where it endures intense insolation, freeze-thaw cycles and a short snow-free growing season.
The species forms low, compact tufts or loose cushions from a branched, somewhat woody caudex. The leaves are small, crowded into basal rosettes, narrowly spathulate to oblong and entire or obscurely toothed, often slightly fleshy and ciliate at the margins, adaptations reducing water loss in the desiccating alpine environment. Flowering stems are short and few-flowered, bearing solitary or few yellow flowers; each flower has five spreading petals, often dotted with orange near the base, ten stamens, and a bicarpellate, partly inferior ovary maturing into a capsule that releases numerous minute seeds.
Saxifraga vacillans belongs to the large and taxonomically complex genus Saxifraga, the yellow-flowered Himalayan members of which (section Ciliatae and allies) form a notoriously difficult species complex. Its apparent rarity and restriction to Bhutan may partly reflect under-collection in remote alpine terrain rather than genuine narrow endemism. Nonetheless, as a specialised high-elevation taxon it is potentially vulnerable to upslope habitat compression driven by climate warming, underscoring the value of continued botanical survey in the Bhutanese high passes.
Author: Harry Sm. · Sources: POWO (Kew), GBIF, Flora of Bhutan Vol. 1, Flora of China Vol. 8, Pan et al.: Monograph of Saxifraga (Saxifragaceae)