(W.W.Sm.) Al-Shehbaz & Warwick
Description
Aphragmus serpens is a diminutive alpine crucifer of the eastern and central Himalaya, recorded from India, Nepal, Bhutan and China, with some 74 georeferenced occurrences indicating a scattered but recurrent presence across the high ranges. It is a plant of cold, open alpine habitats — gravelly and stony slopes, moraine debris, rock ledges and the margins of snow-melt seepages — typically well above treeline. The illustrated material from below Dzongri in Sikkim, at about 3850 m and photographed in August, is representative of the late-summer flowering of this species in the moist eastern Himalayan alpine zone.
The plant is a small, low-growing perennial with a slender, often creeping or trailing habit reflected in the epithet serpens. It arises from a thin rootstock and forms loose tufts or mats of mostly basal leaves; these are small, entire to slightly toothed, narrowed to a petiole, and more or less glabrous to sparsely hairy. The inflorescence is a short, few-flowered raceme; the flowers are typically cruciform with four small petals, usually white to pale lilac or pinkish, four sepals and the characteristic tetradynamous androecium of six stamens. The fruit is a short, oblong to ovoid silicula containing few seeds, the slender style persisting at the apex.
The genus Aphragmus comprises a small group of high-alpine Asian crucifers whose generic limits and species circumscriptions have been substantially revised, this combination being attributed to Al-Shehbaz & Warwick in the course of modern molecular and morphological reassessment of the Brassicaceae. As a specialist of severe high-altitude environments, A. serpens is intimately tied to short, cool growing seasons and reliable snow-melt moisture, and its restricted alpine niche makes it potentially sensitive to climatic warming, though its wide if sparse distribution suggests it is not at present under acute threat.
Author: (W.W.Sm.) Al-Shehbaz & Warwick · Sources: POWO (Kew), GBIF, Flora of China (Brassicaceae), Flora of Bhutan, Al-Shehbaz: monographic revisions of Himalayan Brassicaceae