Centranthus is a genus of flowering plants in the family Caprifoliaceae, order Dipsacales, native to the Mediterranean region. The genus has a complex modern taxonomic history: most major authorities, including Plants of the World Online and World Flora Online, now treat Centranthus as a synonym of the larger genus Valeriana, with its species transferred accordingly. However, the name Centranthus — and in particular the epithet Centranthus ruber — remains in widespread horticultural use.
Plants of the former Centranthus are perennial or annual herbaceous species, distinguished from other valerians by an unusual floral characteristic: the flowers exhibit "handedness," possessing neither radial nor bilateral symmetry, a trait unique among the Caprifoliaceae. The most familiar species, formerly Centranthus ruber (now Valeriana rubra), is a multi-stemmed perennial growing to 80 cm, with opposite, oval to lanceolate leaves 5–10 cm long and dense terminal cymes bearing dozens to over a hundred small tubular flowers in red, pink, or white. Fruits carry feathery projections enabling wind dispersal, and plants can self-seed prolifically.
The genus ranges across the Mediterranean basin, from the Iberian Peninsula eastward to Greece and Turkey and south to North Africa. Several species grow in rocky, disturbed ground, on old walls, and in alkaline soils. The best-known member, Valeriana rubra, has been widely introduced as a garden ornamental and is now naturalized in western Europe, Australia, and western North America, where it can become invasive in disturbed habitats.
Etymology
The name Centranthus is derived from the Greek kentron ("spur") and anthos ("flower"), referring to the characteristic nectar spur at the base of the corolla tube. The common species name ruber is Latin for "red," describing the typical flower colour.
Distribution
Centranthus species are native to the Mediterranean region, ranging from Portugal and Spain through France, Italy, the former Yugoslavia, Albania, Greece, and European Turkey, and from Morocco to Algeria and Tunisia. The best-known species, Valeriana rubra (syn. Centranthus ruber), has been naturalized in France, Great Britain, Ireland, Australia, and several western U.S. states including California, Arizona, Utah, Washington, and Oregon, typically in disturbed rocky places at low elevations.
Ecology
Plants of this genus tolerate highly alkaline soils and are frequently found growing on old stone walls, rocky roadsides, cliffs, and urban wasteground. Flowers are pollinated by bees and butterflies. Fruits bear feathery projections that aid wind dispersal, enabling prolific self-seeding; in some regions (e.g., the Western Cape of South Africa) Valeriana rubra is classified as a compulsory-control invasive species (NEMBA Category 1b).
Cultivation
Centranthus ruber (red valerian) is a long-established garden ornamental prized for its abundant flowers over a long season. It performs well in dry, poor, and alkaline soils. Cultivar 'Albus' bears white flowers (occurring in roughly 10% of wild individuals); 'Coccineus' is noted for an especially extended blooming period. Plants flower from early summer through fall in cooler climates and spread readily from self-sown seed.
Taxonomy Notes
Centranthus was established as a distinct genus in 1805, having originally been described by Linnaeus under Valeriana in 1753. By 2019, Plants of the World Online and World Flora Online returned all Centranthus species to Valeriana, treating Centranthus as a synonym. GBIF's backbone taxonomy continues to list Centranthus as an accepted genus (with 1 recorded descendant), reflecting the lag between checklist updates. The former genus is notably characterized by asymmetric ("handed") flowers — a morphological trait unusual within Caprifoliaceae and used historically to separate it from Valeriana.
