Lithraea is a small South American genus of four species of resinous trees and shrubs in the cashew family, Anacardiaceae (order Sapindales). The genus was formally described by Miers ex Hook. & Arn. and published in Travels in Chile and la Plata (1826), with Lithraea caustica (Molina) Hook. & Arn. designated as the type species.
Plants in the genus are dioecious — individual trees bear either male or female flowers — and produce a caustic, resinous sap notorious for causing contact dermatitis in sensitive individuals. Leaves are alternate and leathery (coriaceous), either simple or composed of three to five leaflets with winged rachis and petioles. Flowers are small and pentamerous, arranged in axillary or terminal panicles, with an androecium of ten stamens. The fruit is a drupe.
The genus is native to South America, with its range spanning Argentina, Bolivia, Brazil, Chile, Paraguay, and Uruguay. The best-known species, Lithraea caustica (litre), is notable in Chile for its potent allergenic sap. Lithraea molleoides (aruera) occurs in Brazil and Argentina.
Etymology
The genus name Lithraea derives from the Greek lithron (λίθρον), meaning blood or gore — an allusion to the caustic, irritating sap that characterises the group. A synonym Lithrea Hook. is occasionally encountered in older literature.
Distribution
Lithraea is native to South America, occurring in Argentina, Bolivia, Brazil, Chile, Paraguay, and Uruguay. The genus occupies a broad latitudinal range across the Southern Cone and adjacent regions.
Ecology
Members of Lithraea produce a strongly caustic resinous sap that can induce allergic contact dermatitis in humans; L. caustica (litre) in Chile is particularly well known in this regard. The plants are dioecious, so populations require both male and female individuals for reproduction. Fruits are drupes, likely dispersed by birds or mammals.
Taxonomy Notes
The genus was described by the British botanist John Miers (ex Hook. & Arn.) and published in 1826. The type species is Lithraea caustica (Molina) Hook. & Arn. A synonym Lithrea Hook. appears in some older works. GBIF recognises four accepted species; the Spanish Wikipedia and some botanical treatments list three, reflecting ongoing uncertainty about the status of L. patagonica.
