Rhodiola pachyclados, the gray stonecrop, is a species of succulent flowering plant in the family Crassulaceae. It is an evergreen, succulent plant native to Pakistan and Afghanistan, but widely cultivated as an ornamental plant. It was formerly included in the genus Sedum.
Rhodiola pachyclados was originally described as Sedum pachyclados by J. E. T. Aitchison and William Hemsley in 1880. Hideaki Ohba transferred it from Sedum to a new genus, Rhodiola, in 1976.
Rhodiola pachyclados looks somewhat like plants in the genus Rosularia, but it can be identified by its broad-based radical leaves. It also differs from Rhodiola primuloides, of which it was once considered a subspecies, by having shallowly lobed radical leaves, petals with smooth edges, and flower clusters containing 3âÂÂ8 flowers.
Rhodiola pachyclados grows 2âÂÂ3 cm tall and spreads through thin, underground stems called rhizomes, which are 2âÂÂ4 mm wide. It forms clusters of rosettesâÂÂcompact, circular arrangements of leavesâÂÂeach with 12âÂÂ18 thick, bluish-green evergreen leaves about 1.5âÂÂ2.5 cm across. Below these, a few withered old leaves may persist. The lower leaves (radical leaves) are broad and oval-shaped, measuring 4âÂÂ10 mm long and 2.7âÂÂ6 mm wide. Their edges may have shallow lobes (small rounded projections) or be smooth, and they gradually narrow at the base. The short leaf stalk (petiole) is broad and flattens out towards the base. The rosettes create tight, cushion-like hummocks, often appearing impenetrable to other vegetation.
Each rosette of Rhodiola pachyclados produces a single flowering stem, which has small, narrow, spoon-shaped leaves attached directly to it (without stalks). These leaves are 4âÂÂ5.5 mm long and 1.6âÂÂ2.2 mm wide. The flowers form a rounded cluster, called inflorescence, measuring 0.8âÂÂ2 cm across and usually contain 3âÂÂ8 individual flowers. The flowers are 3.5âÂÂ4.5 mm across and grow on tiny, hairless stalks (pedicels) that are 0.5âÂÂ1 mm long. The greenish outer flower parts (sepals) are 3.6âÂÂ4 mm long and shaped like stretched-out ovals. The inner, petals, are 6âÂÂ7 mm long, slender, and gradually widen towards the tip. Their edges are smooth. The stamens (pollen-producing structures) are shorter than the petals, and the anthers (pollen sacs) are reddish. The nectary glands are oblong and reddish, measuring 0.7âÂÂ0.9 mm long. The seed-producing structures (carpels) are 6.5âÂÂ7.5 mm long, each containing 8âÂÂ12 ovules (developing seeds). The styles (slender structures that connect the ovary to the stigma) are 1.5âÂÂ2 mm long.
Rhodiola pachyclados is native to the Western Himalayas of Afghanistan and Pakistan, occurring at elevations between 2,400 and 3,400 meters. It has rapidly gained popularity in cultivation as an ornamental plant. In the 1970s, it was primarily referenced in scientific literature, but by 1994 it had become widely propagated, with demand exceeding supply. Under favorable conditions, R. pachyclados forms a dense mound up to 45 cm across within five years. It readily spreads over rocks and can overtake smaller, weaker plants. The species is highly adaptable and, unusually for a succulent plant, performs well in cold, wet winters, better even than when kept dry under shelter.