Thamnosma is a small genus of flowering plants in the family Rutaceae (the rue or citrus family), placed within the order Sapindales. The genus was described by the American botanist and explorer duo John Torrey and John C. Frémont (Torr. & Frém.), and it currently encompasses roughly a dozen accepted species according to GBIF.
Plants in the genus are commonly called desertrues, reflecting both their arid habitats and their membership in the rue family. The most widely known North American species, Thamnosma montana Torr. & Frém., bears the vernacular names turpentinebroom, Mojave desert rue, and Dutchman's breeches, the name "turpentinebroom" alluding to the strong, resinous scent characteristic of these plants. Thamnosma texana (Gray) Torr., the Texas desert rue, is native to the southern United States, while Thamnosma africana occurs in southern Africa (known locally as sandboegoe).
The genus has a geographically scattered distribution spanning arid and semi-arid regions: North America (Mojave and Chihuahuan deserts and adjacent areas of the southwestern United States and Mexico), Texas, southern Africa, and the Horn of Africa region including Somalia and the island of Socotra. This disjunct range across multiple continents in warm, dry climates is a defining biogeographic feature of the genus.
As members of Rutaceae, thamnosma plants share the family's characteristic oil glands, which give the foliage its pungent, turpentine-like aroma when crushed.
Etymology
The genus name Thamnosma was given by John Torrey and John C. Frémont. The plants are colloquially known as desertrues, a name that reflects their arid habitats and their classification within the rue family (Rutaceae).
Distribution
Thamnosma has a disjunct distribution across warm, dry regions: species occur in the Mojave and Chihuahuan deserts and surrounding areas of the southwestern United States, in Texas, in southern Africa (T. africana), and in the Horn of Africa region including Somalia (T. somalensis) and Socotra (T. socotrana).
