Strobilanthes is a large genus of flowering plants in the family Acanthaceae, comprising approximately 350 accepted species (with over 550 total taxa recognized in the GBIF backbone). The genus was described by the Dutch botanist Carl Ludwig Blume in 1826, published in his Bijdragen tot de Flora van Nederlandsch Indië. Plants in the genus are known in English as "coneflowers" or, in the case of the popular ornamental S. dyeriana, "Persian shield."
Members of Strobilanthes are predominantly herbs and shrubs native to tropical and subtropical Asia, ranging from Afghanistan and the Himalayas across South and Southeast Asia to China, Japan, and the Philippines, with additional representation in Madagascar. The flowers are characteristically two-lipped and hooded, appearing in shades of blue, violet, pink, and white. One of the most ecologically distinctive traits of the genus is its tendency toward plietesial (mast) flowering — many species bloom gregariously at long intervals, the most famous being S. wightii, which flowers en masse every 13 years, triggering ecological cascades in the forests of the Western Ghats.
In cultivation, Strobilanthes dyeriana (Persian shield) is the most widely grown ornamental, prized for its iridescent dark-green foliage striped with brilliant metallic purple — a colour produced by light interference in the leaf cells rather than pigment. It thrives in frost-free climates (USDA hardiness zones 9–10) and has received the Royal Horticultural Society's Award of Garden Merit. S. atropurpurea, by contrast, is a temperate-tolerant species from Siberia grown for its purple flowers. Most species are frost-tender and perform best in humid, sheltered conditions that replicate their tropical forest understorey origins.
Etymology
The genus name Strobilanthes derives from the Greek words strobilos (a pine cone or spiral) and anthos (flower), referring to the cone-like, spirally arranged bracts that subtend the flowers in many species. The Thai vernacular name ห้อม (hom) reflects the traditional use of certain species, particularly S. cusia, as a source of indigo-like blue dye.
Distribution
Strobilanthes has its centre of diversity in tropical and subtropical Asia. Its native range spans from Afghanistan and Pakistan westward through the Himalayan foothills (West Himalaya, East Himalaya, Assam) and across the Indian subcontinent to Sri Lanka and Bangladesh, continuing through Southeast Asia (Myanmar, Thailand, Laos, Cambodia, Vietnam, Malaysia, Borneo, Sulawesi, Sumatra, Java, Philippines, Maluku) and northeast into China (south-central, southeast, and north-central regions), Japan, Korea, and Taiwan. Tibet and Nepal are also within the native range, as are the Andaman and Nicobar Islands and New Guinea. A small number of species reach Madagascar.
Several species have been introduced beyond their native range, with naturalized or cultivated populations recorded in the Caribbean (Cuba, Haiti, Dominican Republic, Jamaica, Puerto Rico, Trinidad and Tobago), Central America (Belize, El Salvador, Honduras, Nicaragua, Panama), the southern United States (Florida, Louisiana, Hawaii), Pacific islands (Fiji, Samoa, Cook Islands, Society Islands), and the Indian Ocean islands of Mauritius and Réunion. Casual records exist for Great Britain and New Zealand.
Ecology
The ecology of Strobilanthes is dominated by the phenomenon of plietesial (or mast) flowering — the production of flowers and seeds at long, synchronized intervals rather than annually. S. wightii, native to the Nilgiri Hills of southern India, is the most celebrated example, flowering every 13 years and triggering rodent population explosions due to the sudden abundance of seed. Other species have cycles of 7, 12, or 16 years. Mass-flowering events can lead to dramatic landscape-level color changes, with hillsides turning blue-purple.
Most species occupy the understorey of tropical and subtropical forests, where they tolerate shade and high humidity. Strobilanthes species serve as larval host plants for certain moths; Endoclita malabaracus (Lepidoptera: Hepialidae) has been documented feeding on S. callosa. The genus occupies a broad elevational range across the Himalayan foothills and the hill forests of Southeast Asia.
Cultivation
The most widely cultivated member of the genus is Strobilanthes dyeriana (Persian shield), a tender tropical shrub from Myanmar grown primarily for its spectacular iridescent foliage — dark green leaves overlaid with broad bands of metallic purple and silver. It is reliably perennial only in frost-free climates (USDA zones 9–10), but is commonly grown as an annual or overwintered indoors in cooler regions. It has received the Royal Horticultural Society's Award of Garden Merit. Plants grow best in moist, well-drained, humus-rich soil with partial shade; intense direct sun can bleach the metallic coloration.
Strobilanthes atropurpurea, a hardier species from eastern Siberia and temperate Asia, is valued in cooler temperate gardens for its spires of blue-purple, tubular flowers produced in late summer and autumn. It can tolerate light frost. Strobilanthes anisophylla (goldfussia) is another species occasionally cultivated as a conservatory or houseplant for its purple flowers and attractive foliage.
Propagation
Strobilanthes dyeriana and related tender species are commonly propagated by softwood stem cuttings taken in spring or early summer, rooted under humid conditions with bottom heat. Because Persian shield does not flower reliably in cultivation (and plietesial species in particular may not flower for many years), vegetative propagation is the primary means of maintaining cultivated stock. Hardier species such as S. atropurpurea can be raised from seed sown under glass in spring, or divided in spring from established clumps.
Taxonomy
The genus Strobilanthes Blume (1826) belongs to the tribe Ruellieae within the subfamily Acanthoideae of Acanthaceae. It is one of the largest genera in Acanthaceae, with around 350 accepted species — though total taxon counts including synonyms and doubtful taxa exceed 550 in the GBIF backbone. The genus has historically been subject to broad circumscription and has absorbed several segregate genera. Species have been described by numerous authors across different centuries, including Nees, C.B. Clarke, Bremekamp, and J.R.I. Wood, reflecting ongoing revisionary work. Strobilanthes cernua is the type species. The publication of the genus was in Blume's Bijdragen tot de Flora van Nederlandsch Indië (1826), pp. 781 and 796.
Cultural uses
Several Strobilanthes species have traditional uses as sources of blue dye in Asia. S. cusia (syn. Baphicacanthus cusia) has long been used in Yunnan province of China and across upland Southeast Asia to produce indigo-blue dye for textiles, particularly among hill-tribe communities in Thailand, Myanmar, and Laos — reflected in the Thai vernacular name ห้อม (hom) applied to the genus. The dye is extracted by fermenting the leaves in water, then oxidizing the resulting liquid with lime. Some species are also used in traditional medicine in South and Southeast Asia, though specific pharmacological uses vary by region and species.
