Acnistus is a genus of flowering plants in the nightshade family Solanaceae, order Solanales. As of 2023, it is treated as a taxonomic synonym of the genus Iochroma, a group of about 34 species of shrubs and small trees. Plants in this group are native to the forests of Mexico, Central America, and South America, ranging from Mexico to southern Brazil.
These shrubs and small trees bear alternate, simple, entire leaves and produce showy tubular or trumpet-shaped flowers that are hummingbird-pollinated. Blooms may be blue, purple, red, yellow, or white, maturing into pulpy berries. The calyx is cupular (cup-shaped) and inflated in some species. Iochromas are placed in the subtribe Iochrominae alongside the related genera Dunalia, Eriolarynx, Saracha, and Vassobia. The genus was established by George Bentham in 1845.
The only species historically classified under Acnistus is Acnistus arborescens, now treated as Iochroma arborescens. Iochroma species are cultivated as ornamental flowering shrubs in temperate and subtropical gardens, though most require frost protection in cooler zones. Several species contain bioactive withanolides and have been used in traditional medicine.
Etymology
The genus Iochroma was established by George Bentham in 1845. The origin of the name is uncertain.
Distribution
Iochroma (which now includes Acnistus) is native from Mexico to southern Brazil, with species found in the forests of Mexico and South America.
Ecology
Iochroma flowers are hummingbird-pollinated and also attract bees. Species grow in forest habitats across their range from Mexico to South America.
Cultivation
Iochroma species are cultivated as flowering ornamentals. Hardy in USDA zones 7–10 depending on the species; most are not frost-hardy and must be overwintered under protection in cooler zones. They are commonly trained as standards (topiary).
Taxonomy
As of February 2023, Plants of the World Online treats Acnistus as a synonym of Iochroma. Iochroma belongs to the subtribe Iochrominae within Solanaceae, alongside Dunalia, Eriolarynx, Saracha, and Vassobia. The genus was established by George Bentham in 1845 and is currently divided into three sections. Acnistus arborescens is reclassified as Iochroma arborescens (L.) J.M.H.Shaw.
Cultural Uses
Iochroma fuchsioides is used by Kamsa medicine men of the Sibundundoy valley in the Colombian Andes for difficult diagnoses. Iochroma species contain withanolides and hydroxycinnamic acid amides with potential pharmaceutical value.
