Wall.
Description
Arenaria densissima is a high-alpine cushion sandwort of the Sino-Himalaya, recorded from China (CN), Nepal (NP) and Bhutan (BT), with 159 GBIF occurrences reflecting its restricted upper-montane to alpine distribution. It is a plant of stony alpine turf, gravelly slopes, screes and exposed ridges, typically between about 3800 and 4800 m, where the dense cushion habit is an adaptation to cold, wind and intense radiation. The illustrated collections were made at Chele-La in Bhutan at around 4000 m and at the Churta-Khola in West-Nepal at about 3900 m, both in June at the start of the alpine flowering season.
It is a small, mat- or cushion-forming perennial herb with a woody, branched rootstock giving rise to densely crowded, congested shoots that form low compact tufts. The leaves are small, sessile, linear to subulate and rigid, closely imbricate and often spine-tipped, creating the dense mossy cushion alluded to by the epithet densissima. The flowers are small, solitary or few, sessile or shortly pedicellate among the leaves; they have five free, ovate sepals, five entire white petals, ten stamens and a superior ovary with styles. The fruit is a small capsule dehiscing by valves or teeth to release minute seeds.
Arenaria, in the family Caryophyllaceae, is a large genus well represented in the high mountains of Asia, where the cushion growth-form has evolved repeatedly as a convergent response to the alpine environment. Species such as A. densissima are characteristic of the Himalayan high-alpine cushion-plant communities and are of biogeographic and ecological interest as pioneers stabilising substrate and providing microhabitats in the cold desert and alpine zones.
Author: Wall. · Sources: POWO (Kew), GBIF, Flora of China, Flora of Nepal, Flora of Bhutan, Monograph of the genus Arenaria (McNeill)