Hydnocarpus Gaertn.

Trees, sometimes shrubs, usually dioecious, occasionally monoecious (H. castanea, H. curtisii). Leaves alternate, entire or serrate, penninerved; petioles thickened at the apex. Stipules mostly early caducous. Male flowers in axillary (rarely supra-axillary) peduncled and ± branched cymes (these sometimes very short or reduced to ± sessile fascicles, very rarely to a solitary flower) from younger branches, or rarely in elongate raceme-like panicles from the trunk or the old branches. ♀ Flowers similarly arranged, but mostly solitary or in (very shortly peduncled) fascicles of 2-3 from the axils of young branches. Bracts small or minute, sometimes subpersistent. Sepals (3-)4-5, rarely 7-11, free or rarely slightly connate at the base, concave, ± equal, imbricate, ± reflexed at anthesis, caducous. Petals 4-5, rarely up to 14, free or rarely slightly connate at the base, mostly membranous, with a somewhat fleshy and mostly densely pilose scale at their inner base, caducous. ♂ Flowers: stamens 5-∞(-115); filaments free, sometimes very short; anthers oblong to ovate-cordate or didymous; cells divergent by the dilated connective. Rudimentary ovary sometimes present. ♀ Flowers: staminodes 5-∞, their anthers mostly reduced in size and sterile, or entirely absent. Ovary sessile, unilocular, with 3-6 placentas. Stigma sessile, with 3-5 short or elongate radial branches, these mostly dilated towards the apex and shortly bifid, rarely narrow, ± reflexed. Fruit indehiscent, globose or ovoid, rarely cylindrical or cucumber-like, few-to many-seeded; pericarp thick and hard to thin and fragile; exocarp brown, sometimes with distinct fibrose structure; mesocarp light-yellowish, very hard (stone-cells), H. cauliflora excepted; endocarp soft, mostly granular, dark-brown. Seeds densely packed in a pulp, angular-ovoid, with a membranous aril and very hard testa. Endosperm albuminous-oily. Embryo erect; cotyledons foliaceous.

Most species occur as substage shrubs or trees in evergreen rain-forests at low altitudes.

Uses. The oil extracted from the seeds of the greater part of the species is used for curing wounds and eczemes by the native peoples since very old times, especially in China, where the seeds are imported up to the present time. The oil of the Burmese H. kurzii is known as 'chaulmoogra-oil'; since 1854 is has been used as a remedy against lepra, but this has practically been abandoned today in Hawaii. It contains the glycerides of 2 fatty acids, viz chaulmoogric acid and hydnocarpic acid. These acids occur also abundantly in certain Malaysian representatives as H. alcalae, H. cauliflora, H. subfalcata, and H. woodii (cf. H. Schlossberger Chaulmoograol und Verwandtes Heffter Handb. Pharmak., Erg.-Werk vol. 5 1937 , containing a complete review on the subject). To cover the great need of chaulmoogra-oil, three species are or have been cultivated in tropical areas: H. kurzii (from Burma), H. alcalae (from the Philippines) and H. anthelminthica Pierre (from Indo-China). Besides the above-mentioned fatty acids theseeds of several species contain glycosides which discharge hydrocyanic acid; they are used for fishpoisoning in the same manner as those of Pangium edule.