The paper provides a key for identification and a checklist of mycoheterotrophic species of the genus Exacum, representing a well-defined group of achlorophyllous members of Gentianaceae regarded sometimes in the limits of a separate genus Cotylanthera. One novel species, E. zigomorpha, discovered in northern Vietnam, is described and illustrated as new for science. Among other features the discovered species strikingly differs from its congeners in having distinctly zygomorphic flowers.
Small achlorophyllous herb with erect, slender, branched stem; leaves, opposite, scale–like; flowers hardly opening, white, asymmetric; calyx decussate, bisymmetric, 1–1.2 cm across; corolla of 4 petals, 1–1.2 cm long, zygomorphic; petals narrowly oblong, 2.5–3 mm wide, joined at the base; androecium slightly zygomorphic, one-side turned; anthers yellow, 4 × 1 mm long; ovary of 2 carpels, 1-locular, almost globular 1.5 mm in diam.; style thread-like, 8–8.5 mm long; stigma entire.
Leonid V. Averyanov, Khang Sinh Nguyen, Hiep Tien Nguyen
For final version please see at: http://biotaxa.org/Phytotaxa/article/view/phytotaxa.183.2.3