Clarkia is a genus of approximately 40–50 annual flowering herbs in the evening-primrose family (Onagraceae), formally described by Frederick Pursh in 1814. The genus is named in honor of Captain William Clark of the Lewis and Clark Expedition. Plants grow either prostrate or erect to less than 2 metres, with simple leaves ranging from 1–10 cm long depending on the species. The showy flowers each have four sepals and four petals in shades of white, pink, purple, or red, frequently spotted or streaked, and are sometimes described as resembling small hollyhocks. Fruits are elongated cylindrical pods, typically 4-grooved or 8-grooved, containing numerous tiny seeds.
Nearly all species are native to western North America, where they bloom late in the wildflower season — hence the widely used common name "farewell to spring" applied especially to Clarkia amoena. A single exception, Clarkia tenella, is native to South America (Chile and Argentina). The genus has been expanded over the years to absorb formerly separate genera including Godetia and Eucharidium, making Clarkia the accepted name for the entire group.
In the garden, clarkias are valued for their ease of cultivation. They thrive in full sun to partial shade with light, well-drained soil of modest fertility, and prefer cool nights; sustained heat inhibits flowering. They are grown from seed sown directly on the soil surface, since the seeds need light to germinate. Several species — particularly C. unguiculata (mountain garland), C. amoena (farewell to spring), and C. bottae — are popular ornamentals in temperate gardens.
Etymology
The genus name Clarkia was coined by the botanist Frederick Pursh in his 1814 work Flora Americae Septentrionalis, honoring Captain William Clark, co-leader of the Lewis and Clark Expedition (1804–1806) that explored the western United States. Specimens of the type species, Clarkia pulchella, were among the plant collections brought back from the expedition. In some botanical discussions the genus has informally been suggested to be renamed "Yorkia" to recognize York, the enslaved African-American member of the expedition, though this name has no standing in formal nomenclature.
Distribution
Clarkia is almost entirely a western North American genus. Species range across California, Oregon, Washington, Idaho, and adjacent states, with the greatest diversity in California. The single disjunct exception is Clarkia tenella, native to Chile and Argentina in South America. Herbarium records in the SEINet database document the genus broadly across the southwestern United States.
Ecology
Clarkia species occupy a specialist ecological niche as late-season bloomers in open, often disturbed habitats of western North America. They are host plants for sphingid moths (hawk moths) and several other insect species. Most notably, some native bees are oligolectic on Clarkia — including the so-called "clarkia bee," which relies exclusively on this genus for floral resources. This tight pollinator dependency makes the genus ecologically significant for native bee communities in its range.
Cultivation
Clarkias are undemanding annuals well suited to temperate gardens. They prefer a position in full sun to partial shade and thrive in light, sandy soil with good drainage and modest fertility; rich, heavy soils encourage foliage at the expense of flowers. Plants should be allowed to dry out between waterings. They favor cool nights and may stop flowering in sustained heat. In the garden, plants typically reach 60–90 cm (2–3 feet), with spacing of about 20–25 cm (8–10 inches) between individuals. Popular ornamental species include Clarkia unguiculata (mountain garland), C. amoena (farewell to spring), C. speciosa (redspot clarkia), and C. bottae.
Propagation
Clarkia is grown from seed, direct-sown where plants are to flower. Seeds require light to germinate and should be scattered on the soil surface rather than covered. Sowing in autumn (in mild climates) or in early spring produces the best results, taking advantage of cool temperatures that favour germination and establishment before heat sets in.
Taxonomy
Clarkia Pursh (1814) is the accepted genus name for a group of annuals in the family Onagraceae, order Myrtales. The type species is Clarkia pulchella. Several genera once treated separately — notably Godetia and Eucharidium — are now synonymized within Clarkia, consolidating the group into a single accepted genus. GBIF recognizes approximately 100 descendant taxa (species and infraspecific ranks) under the genus, while most botanical treatments cite around 40–50 accepted species. The genus is assigned GBIF usageKey 3189179.
