Exacum is a genus of approximately 75 flowering plant species in the family Gentianaceae, order Gentianales. The genus was formally described by Carl Linnaeus in 1753 in Species Plantarum.
Plants in the genus are primarily annuals with branched, glabrous stems and opposite leaves. Flowers are 4- or 5-merous with a rotate corolla in which the lobes are longer than the tube, typically in shades of blue, mauve, or lilac. The calyx is lobed nearly to the base. Stamens are inserted at the throat of the corolla tube; anthers are cylindric and dehisce through apical pores. The ovary is 2-locular and the fruit is a 2-valved capsule with many seeds bearing a warty seed coat. Inflorescences are axillary or terminal paniculate cymes.
The genus is distributed across tropical and subtropical regions of sub-Saharan Africa, the southern Arabian Peninsula, southern and southeast Asia (including India, China, and Southeast Asia), Madagascar, New Guinea, and Australia. Two species occur in China: Exacum tetragonum and Exacum teres.
Distribution
Exacum is native to tropical and subtropical regions spanning sub-Saharan Africa, the southern Arabian Peninsula, south and southeast Asia (including India, China, and Southeast Asia), Madagascar, New Guinea, and Australia. Approximately 40 species occur in tropical Africa and Asia combined, with just two species — E. tetragonum and E. teres — recorded for China.
