Phlox is a genus of roughly 67 to 70 species of mostly herbaceous flowering plants in the family Polemoniaceae, established by Carl Linnaeus in Species Plantarum (1753). The genus name comes from the Ancient Greek phlox, meaning "flame," a reference to the intense colour of the flowers in many species. The group is best known to gardeners as the source of garden phlox, moss phlox, woodland phlox, and the annual Drummond's phlox, but the wild diversity is far broader and concentrated in North America.
Plants in the genus span a striking range of growth forms. Some species, such as Phlox paniculata, are upright herbaceous perennials reaching up to about 1.5 metres in height, while others, including Phlox subulata and Phlox hoodii, form dense low cushions or mats only a few centimetres tall. Most species are perennial, though a handful — notably Phlox drummondii — are annuals. Leaves are usually opposite and linear to lanceolate, and many species form cespitose tufts.
Flowers are borne in terminal clusters of one to several blooms per stem and have a distinctive salverform corolla — a slender tube that flares abruptly into a flat, five-lobed face. Colour ranges across white, pink, magenta, red, lavender, violet and pale blue, and many species and cultivars are fragrant. The fruit is a small ovoid to ellipsoid capsule that splits longitudinally along three or more valves, often releasing its one or two seeds per chamber with an explosive snap.
The genus is overwhelmingly North American, with native species occurring from Alaska across Canada and the contiguous United States south into northern Mexico, and with particular richness in the southwestern US and the Colorado Plateau. A single outlying species occurs in Siberia and the Russian Far East, and one additional species reaches southern South America. Habitats range from alpine tundra and rocky talus to open prairie, dry desert montane sites, and moist deciduous woodland — a breadth that helps explain why Phlox species are so widely adapted to garden conditions.
Etymology
The genus name Phlox is taken directly from the Ancient Greek word phlox, meaning "flame." It alludes to the intense, fiery colours seen in the flowers of many species, particularly the magentas and reds that dominate cultivated garden phlox. Carl Linnaeus adopted the name when he formally described the genus in Species Plantarum in 1753.
Taxonomy
Phlox L. was published by Linnaeus in Species Plantarum, volume 1, page 151 (1753), and is the type genus of the family Polemoniaceae within the order Ericales. Plants of the World Online currently accepts 69 species, while Wikipedia's overview cites 68 and regional treatments such as SEINet round the figure to "about 70 species" — the small disparity reflects ongoing splits and lumps within the genus. Four synonyms are recognised by POWO: Lychnidea Hill (homotypic) and the heterotypic Fonna Adans., Armeria L. ex Kuntze, and Phloxus St.-Lag. The genus has an ACCEPTED status in GBIF.
Distribution
Phlox is overwhelmingly a New World genus. Native ranges run from Alaska across Canada and the contiguous United States to northern Mexico, with a particular concentration of species in the western and central US — from the prairies through the Rocky Mountains and into the desert Southwest, including the Sonoran Desert and Colorado Plateau. The single non-American native is a species occurring across Siberia, the Russian Far East and Mongolia, and one further species reaches southern South America. The genus has been introduced and locally naturalised in scattered locations in Europe (Austria, Germany, Great Britain, Italy, Czechia-Slovakia), parts of Asia (Bangladesh, Uzbekistan, Vietnam), and outlying tropical sites including the Galápagos, Trinidad-Tobago and Venezuela.
Ecology
Wild Phlox species occupy habitats ranging from alpine tundra and rocky talus through woodland understorey to open prairie and dry desert mountains. The flowers are visited by a broad suite of pollinators — butterflies, hawk moths and clearwing moths, hummingbirds, and long-tongued bees — and several species (notably P. divaricata in shady gardens) are routinely cited as butterfly and hummingbird plants. The foliage of many Phlox species hosts the larvae of various Lepidoptera, and the plants are browsed by groundhogs, cottontail rabbits and deer in much of their North American range.
Cultivation
Phlox is one of the more adaptable perennial genera in temperate horticulture, with species hardy across roughly USDA zones 3 to 9. Most species perform best in full sun to part shade in a moderately fertile, medium-moisture, well-drained soil, although the genus tolerates clay, loam, sandy and shallow rocky soils, and occasional periods of either dryness or excess moisture. Heights vary dramatically with species — from cushioned 3–6 inch mats of P. subulata up to 1.5 metre stands of P. paniculata — so the genus supplies plants suited to rock gardens, cottage gardens, mixed perennial borders, woodland edges, containers and foundation plantings. Self-seeding is common in favourable sites. Common problems include phlox plant bugs, four-lined plant bugs, oriental beetles, black root rot and Phytophthora blight; deer tend to leave plants alone, but cottontail rabbits will browse them.
Propagation
Phlox species are routinely propagated by seed, division and stem cuttings. Perennial species in particular respond well to division in autumn or spring; basal stem cuttings taken in spring strike readily, and root cuttings can be taken in early autumn or winter for selected species. Seed is the standard method for the annual Phlox drummondii.
Uses
Beyond their dominant role as ornamental garden plants, Phlox species have only limited reported uses. Plants For A Future records no known culinary or medicinal applications for the representative Phlox divaricata, with both edibility and medicinal value rated zero out of five. Practical landscape uses noted in the literature include ground-cover plantings in shaded gardens and use of the fibrous root systems of certain species for soil binding and erosion control.
