Exacum

Exacum is a genus belonging to the family Gentianaceae. There are 20 to 40 herbaceous species found in the Old World; they are annuals, biennials, or perennial plants. E. affine (Balf. f.), a native of Socotra (an island in the Indian Ocean near the entrance to the Red Sea), is the most commercially important species, with several cultivars available in the florist trade. ^{1 , 3} This tender ornamental plant is grown primarily as a flowering plant. It has simple opposite dark green glossy leaves (3.5 cm long) which are sessile to the stem. Blue, dark lavender, or white flowers, which have a mild fragrance, may be single or double and are displayed in forking cymes. The spreading corolla (1.5 cm wide) and calyx are 5 lobed. There are 4 stamens and anthers; the former are golden yellow. In commerce these herbaceous plants are grown as annuals. In nature, they are annuals or biennial and can be some 60 cm in height. E. zeylanicum Roxb. and E. macranthum Am., natives of Sri Lanka, are the most impressive of the exacums, with large rich blue flowers. Some are 4 or 5 cm across, respectively. ^{1 , 3} They are not used as pot plants because they are biennial. ^{1 , 3}