Lithospermum L., commonly called gromwells or stoneseeds, is a genus of flowering plants in the family Boraginaceae. The name comes from the Greek words for "stone" and "seed," a direct reference to the strikingly hard, smooth nutlets that are the genus's most recognizable feature. With roughly 74–84 accepted species recognized by major checklists, Lithospermum is one of the larger genera in the borage family, and its diversity is concentrated in the Americas—particularly the southwestern United States and Mexico—though the genus occurs on nearly every continent in temperate and montane regions.
Plants in this genus are annual or, more often, perennial herbs, typically with bristly or softly hairy stems and leaves. The flowers are funnel-shaped or salver-shaped, often yellow, white, or greenish-white, and are borne in leafy-bracteate cymes. Many species are heterostylic. The fruits are characteristic smooth to pitted or wrinkled nutlets with a basal attachment scar, giving the plants their common name. Several species produce tuberous, pigmented roots that have been used as dyes or medicines across their ranges.
Taxonomically, Lithospermum has expanded in recent decades. A 2009 molecular phylogenetic study established that the genus Onosmodium—historically treated as distinct—falls nested within Lithospermum, leading to its synonymization. Other generic names including Batschia, Macromeria, and Nomosa are now treated as synonyms. The type species is Lithospermum officinale L., the common gromwell of Europe and western Asia.
Etymology
The genus name Lithospermum is formed from two Greek words: lithos, meaning "stone," and sperma, meaning "seed." The name was coined to describe the strikingly hard, stony nutlets that characterize all members of the genus. This etymology is mirrored in the common name "stoneseeds," used alongside "gromwells" for many species.
Distribution
Lithospermum has a nearly worldwide distribution, occurring across temperate and montane regions on most continents. Its center of diversity lies in the Americas, particularly in the southwestern United States and Mexico, where dozens of endemic species are found in grasslands, dry woodlands, and mountainous terrain. The eastern North American range extends from Ontario and Saskatchewan south to Georgia and Texas, where species such as L. caroliniense grow in dry or sandy open woods and prairies. In Europe, L. officinale is the best-known representative and is documented in countries including Switzerland. The genus also includes species endemic to the Andes (e.g., L. peruvianum, L. cuzcoense).
Ecology
Lithospermum species are characteristic plants of open, often dry habitats: prairies, dry or sandy open woodlands, and montane slopes. They favor well-drained, often lime-free soils and require full sun, being intolerant of shade. Insect pollination is standard across the genus, and many species are heterostylic—a floral arrangement that promotes cross-pollination. The foliage is used as larval food by lepidopteran caterpillars; the moth Ethmia pusiella has been recorded on L. officinale.
Cultivation
Lithospermum species suited to gardens generally prefer a warm, sunny position in moderately fertile, well-drained, lime-free sandy soil. They do not tolerate shade. Most temperate species are hardy to USDA zones 3–7. Propagation from seed is the primary method, though division and cuttings are also viable for perennial species.
Propagation
Seeds are sown in spring in a soilless or gritty medium in a cold frame or unheated greenhouse. Seedlings are pricked out into individual pots once large enough to handle and overwintered under protection before planting out the following spring. Established clumps of perennial species can be divided in early spring, and stem cuttings taken in summer are a further option.
Cultural Uses
Lithospermum species have a long history of use by indigenous and traditional cultures across their range. In eastern North America, roots of species such as L. caroliniense were chewed with gum to impart a red color, while flowers were used to produce a yellow coloring. In Japan and East Asia, the root of L. erythrorhizon (zicao in Chinese medicine) has been used for centuries as a source of purple and red dye and as a medicinal herb; modern research has confirmed antiviral activity of its root extracts. Indigenous peoples of the southwestern United States, notably the Shoshone, prepared infusions from a Lithospermum species as a contraceptive.
Taxonomy
Lithospermum L. was described by Linnaeus and is placed in the family Boraginaceae, subfamily Boraginoideae, order Boraginales. The type species is L. officinale L. The genus circumscription has broadened substantially: a 2009 molecular phylogenetic study demonstrated that Onosmodium Michx. is nested phylogenetically within Lithospermum, resulting in its treatment as a synonym. GBIF also recognizes Batschia, Cyphorima, Lasiarrhenum, Macromeria, Nomosa, Osmodium, Pentalophus, Perittostema, Psilolaemus, and Purshia as synonyms. Species counts vary by authority: GBIF lists 74 accepted species, while Plants of the World Online recognizes 84.
History
The earliest formal botanical treatment of Lithospermum as a genus is attributed to Linnaeus. A Late Miocene fossil species, †Lithospermum dakotense, is known from the Ash Hollow Formation in South Dakota, with nutlets closely resembling those of the extant L. caroliniense and L. incisum—indicating that the genus's hard, stony nutlets have been morphologically stable for millions of years. The genus boundaries were significantly revised following a 2009 molecular phylogenetic study that led to the absorption of Onosmodium and several other segregate genera.
