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Trees or shrubs, glabrous (in Mal.). Bark at base of stem exuding yellow resinous sap, hardening black. Branchlets compressed, 4(-6?)-lined, with interpetiolar scars linear, closed (continuous and straight or curved upward) or open (interrupted and curved downward) (). Leaves opposite or rarely subopposite, entire, sessile or petioled, often with fine translucent ('pale') glandular dots, without black or red glands. Inflorescences terminal, racemiform, paniculate to axillary racemes or single flowers. Flowers (except staminodial fascicles and gynoecium) 5-merous, sometimes heterodistylous. Sepals quincuncial-imbricate, coriaceous, persistent, with longitudinal pale or black glandular lines or dots, sometimes elongating in fruit. Petals deep crimson to pink or white, sometimes tinged orange or green, with reddish or black glandular dots or lines (), sometimes with nectariferous scale-like, basal appendage (, , ), caducous to subpersistent. Stamen fascicles united 2+2 + 1, single one epipetalous and double ones episepalous, glabrous, caducous, each with ∞ stamens; filaments crimson to white, slender, united for over half their length; anthers crimson to white, ± shortly oblong to rhombic, dorsifixed, sometimes with 1-2 brown resiniferous glands terminating the connective. Staminodial fascicles 3, alternating with the fascicles, varying in shape and size (, ). (Flowers with 4-5-merous inner whorls occasionally occur). Ovary incompletely 3-celled; styles 3, free, ± slender, stigmas small, ± capitate. Ovules ∞-4 on the basal half of each placenta, erect or ascending. Fruit a loculicidal, 3-valved, ± ligneous capsule, with slightly prominent longitudinal vittae. Seeds ∞-4 on each woody placenta (columella), cylindric to ovoid, imbricate; testa not sculptured; winged unilaterally or all round; embryo cylindric, straight, with cotyledons longer than the hypocotyl.


Asia-Tropical: India present; Maluku (Maluku absent); New Guinea absent, S. China present, continental Asia present, east of 92°E present, south of c. 24°N and including Hong Kong and Hainan present
6 species, occurring in continental Asia from India (east of 92°E) east to S. China (south of c. 24°N and including Hong Kong and Hainan) and throughout Malesia, but not in the Moluccas and New Guinea. .


The bodies described above as staminodial fascicles have been the subject of much investigation. Morphological and anatomical evidence indicates that they are sterile members of the episepalous androecial whorl (see ); but, whereas the five fertile members of the epipetalous whorl are still present (four of them united in pairs to form double fascicles opposite sepals), the three sterile members of the episepalous whorl are all single organs i.e. two members of this whorl do not develop.
Heterodistyly occurs regularly in sect. Tridesmos and C. cochinchinensis and may be an occasional feature of other species. It is also present in the closely related genus Eliaea. This tendency towards specialized insect pollination is accompanied by the development of nectariferous petal appendages (absent in sect. Cratoxylum). In addition, the flowers of those species in which heterodistyly is most pronounced tend to be pseudo-tubular, i.e. to have erect rigid sepals which prevent the petals from spreading. In these species (at least), the sterile fascicles probably act like the lodicules of grasses by swelling and thus aiding the expansion of the sepals and petals from the bud (see ).


Species of sect. Cratoxylum and Tridesmos have hard, heavy wood. C. sumatranum is good for making charcoal and implements. C. cochinchinense has fairly durable wood, but is not used much for timber. Species of sect. Tridesmos, on the other hand, give a flexible durable timber, which is sometimes used by Indonesians for construction. The species of sect. Isopterygium have rather soft, red wood that splits badly and blunts tools on account of its high silica content. The Dayak of Indonesian Borneo, however, make drums of old hollow trunks of C. arborescens.
HEYNE () stated that the bark at the base of the trunk of C.formosum produces a resinous exudate (at first golden yellow, then red, finally black) that is used as a remedy for scabies and leg wounds.


Cratoxylum is closely related to, but distinct from the Madagascan monotypic genus Eliaea CAMBESS., according to GOGELEIN (1967) and BAAS (). It is intermediate in distribution between that genus and Triadenum RAFIN., a herbaceous genus that has been wrongly included in Hypericum but appears to have been derived from Cratoxylum. Triadenum has an E. Asia-E. North American disjunct distribution (Assam, Taiwan, Japan, Korea, Siberia—eastern U.S.A. and Canada).
This account is based largely on the revision of the genus by GOGELEIN (1967).


GOGELEIN 1967 – In: Blumea: 453
SPACH 1836 – In: Ann. Sc. Nat.: 352
Bl. 1852 – In: Mus. Bot. Lugd. Bat.: 18
Blume 1852 – In: Mus. Bot. Lugd. Bat.: 15
Blume 1825: Bijdr.: 144
Corner 1939 – In: Gard. Bull. S. S.: 21
SPACH 1836 – In: Ann. Sc. Nat.: 351
cf. STEEN. 1948 – In: Bull. Jard. Bot. Btzg: 459