Diapensia is a genus of about six species of flowering plants in the family Diapensiaceae, placed in the order Ericales. The genus was first described by Carl Linnaeus in 1753 in Species Plantarum. Most species are concentrated in the Himalaya and adjoining mountains of southwestern China; a single species, Diapensia lapponica, extends across the Arctic and subarctic Northern Hemisphere in a circumboreal, circumpolar distribution. This wide range likely arose after an ancestor related to the Himalayan D. purpurea colonized arctic habitat from North China and Russia.
Species in the genus are small, extremely slow-growing, cushion-forming evergreen dwarf shrubs adapted to exposed, wind-scoured alpine and arctic-alpine habitats such as rocky ridges kept snow-free by high winds. The dense cushion growth habit helps trap heat and shelter the plant from extreme cold and wind. Leaves are small, oval, leathery, and toothless, arranged in dense rosettes; flowers are typically solitary and white, rarely pink. Individual plants can be very long-lived — some populations, aged by growth rings or clump diameter, are thought to persist for over a century.
The genus name Diapensia was coined by Linnaeus, but its exact derivation is disputed. Some authorities trace it to the ancient Greek name for sanicle, a very different-looking plant; others suggest a Greek root related to "five" (referencing the five-parted calyx); still others propose a meaning connected to grief or mourning.
Diapensia lapponica, the genus's most widespread species, reaches its southernmost European limit at a single isolated site in Lochaber, Scotland, discovered in 1951 — one of several Arctic-alpine plant disjuncts found in the Scottish Highlands in the early 1950s. Because Diapensia species are highly sensitive to heat and thrive only in cold, humid, exposed conditions, they are notoriously difficult in cultivation and generally die when moved to lowland gardens; propagation is normally attempted from cold-stratified or winter-collected seed.
Etymology
The genus name Diapensia was applied by Linnaeus, but its derivation is uncertain and disputed among sources: possibly from the ancient Greek name for sanicle, from Greek "dia pente" ("by fives," referencing the five-parted calyx), or from a Greek root meaning "deeply grieving."
Distribution
Most Diapensia species occur in the Himalaya and mountains of southwestern China. The exception, Diapensia lapponica, has a circumboreal, circumpolar Arctic and subarctic distribution across the Northern Hemisphere, likely derived from a Himalayan ancestor that colonized arctic habitat from North China and Russia.
Ecology
Diapensia species are small, slow-growing, cushion-forming evergreen dwarf shrubs of exposed, wind-scoured alpine and arctic-alpine habitats, such as rocky ridges kept free of snow by wind. The compact cushion form traps heat and shelters the plant; individuals are highly sensitive to warm temperatures and often occur in misty, foggy sites. Some populations are extremely long-lived, with individual clumps estimated at over a century old.
Cultivation
Diapensia is difficult to grow outside its native cold, exposed habitat and usually dies when transplanted to lowland gardens. Propagation is typically attempted from cold-treated or wild, winter-collected seed rather than transplants.
Taxonomy Notes
Diapensia is the type genus of the family Diapensiaceae, in the order Ericales, and was described by Linnaeus in 1753 (Species Plantarum 1: 141). Roughly six species are currently recognised.
History
Diapensia lapponica was discovered at its southernmost European site near Glenfinnan, Lochaber, Scotland in July 1951 by birdwatcher C. F. Tebbutt — one of a trio of Arctic-alpine plants newly found in the Scottish Highlands in the early 1950s.
