C.M. Taylor, Oct. 2013: This genus is under revision by P. de Block (BR) who previously revised the African species of Ixora, see that work for details of the genus (De Block, 1998). Ixora is characterized by a woody habit; stipules that are interpetiolar or shortly united around the stem, triangular, and usually persistent with the leaves and apicaly aristate; opposite or occasionally ternate leaves that are generally petiolate, lack domatia, and have the petioles articulated at the base where they attach to the stems; terminal, sessile to usually pedunculate, generally cymose inflorescences with the axes generally articulated; small to large, sessile to pedicellate, four-merous, homostylous flowers with secondary pollen presentation; stigmas with two lobes; and drupaceous fruits with 2 or rarely 3-4 planoconvex pyrenes. The flowers are typically sweetly scented and nocturnal, with a narrow and often long corolla tube. Most species have corollas that are generally white with a pink to red tinge on the outside of the corolla tube, and become yellow with age. The corollas of some species vary markedly in size within the species, by as much as 50% in some cases. The inflorescences of several species often have foliaceous bracts (or reduced leaves) near their bases. The most frequently collected species (at least in recent decades) are Ixora cremixora, Ixora littoralis, and Ixora siphonantha.
Ixora is similar to and frequently confused with Tarenna, which has petioles that are not articulated, usually five-merous flowers, and and an undivided club-shaped stigma; Psychotria, which has petioles that are not articulated, stipules that are generally bilobed and/or deciduous, and usually five-merous flowers; and Pavetta, which has petioles that are not articulated and an undivided club-shaped stigma, and is not known from Madagscar.
In addition to the native Ixora species, several Ixora species are cultivated in warm regions world-wide as ornamentals and can be expected in Madagascar. Two shrubs with leathery elliptic-oblong leaves and flowers with reduced calyx limbs and generally red or orange corollas are widely found world-wide, Ixora coccinea L. with sessile leaves that are rounded to cordate at the base and Ixora chinensis with petiolate leaves that are cuneate at the base; both of these species have cultivated forms with white flowers. Ixora finlaysoniana G. Don has consistently white flowers with well developed calyx lobes and petiolate elliptic leaves, and is documented from the Comores.