Shrubs (sometimes scrambling or rarely somewhat climbing) or rarely small trees, monoclinous or andromonoecious, armed or unarmed, apparently without oil glands. Stipules absent. Leaves alternate, simple, odd-pinnate, or digitately trifoliolate; blades of simple leaves entire at margin, those of compound leaves crenulate, crenate, lobulate, or rarely entire at margin. Flowers solitary and axillary or in terminal and/or axillary cymes, racemes, or rarely thyrses, actinomorphic, hypogynous, 3-5(or 6)-merous. Sepals distinct or connate to ± half their length. Petals distinct, imbricate or narrowly so in bud. Stamens equal to or 2 × as many as petals, inserted in lateral pits on disk or at base of disk; filaments distinct, linear, with or without adaxial ligulate appendage at base; anthers longitudinally dehiscent. Disk within androecium, nectariferous, columnar to barrel-shaped or pulvinate to cup-shaped. Gynoecium 3-5(or 6)-carpelled and -loculed; ovaries axially or ± completely connate; placentation apical-axile; ovules pendulous, solitary or collateral in each locule; style terminal, stylar elements coherent or rarely distinct at base; stigma 3- or 4-branched or capitate (often slightly lobed). Fruit drupaceous, of separating mericarps or ± completely syncarpous, drying brown to black or rarely pale gray-brown when ripe; abortive carpels, if any, persistent; outer pericarp (exocarp and mesocarp) ± fleshy; endocarp bony next to locule(s), otherwise woody, in mericarps developed from 2-ovuled carpels forming a median longitudinal partial partition within locule. Seeds pyriform or rarely irregular in shape; seed coat membranous or thin and brittle; endosperm copious or ± scant, fleshy; embryo relatively large, bent double or rarely broadly horseshoe-shaped; cotyledons plano-convex and linear or ± flattened and elliptic-oblong; hypocotyl superior.
Five genera and 24 species: tropical and S Africa, S and SE Asia, N Australia, Canary Islands, W Mediterranean region, South America, West Indies; one species in China.
So far as is known, Harrisonia belongs with Cneorum Linnaeus, Dictyoloma A. Jussieu, Ptaeroxylon Ecklon & Zeyher, and Spathelia Linnaeus, which together form a monophyletic group, here treated as Cneoraceae, that is sister to Rutaceae s.str. Despite the fact that only rbcL data are known for Harrisonia according to Chase et al. (Amer. J. Bot. 86: 1191-1199. 1999), those authors were correct in excluding Harrisonia from Simaroubaceae. Harrisonia and the other four genera of Cneoraceae have a very similar chemistry, including limonoids (as in Meliaceae and Rutaceae) but no quassinoids (as in Simaroubaceae). These genera do, however, have ptaeroxylans in common, not found in these other groups. It appears that there are no gland dots in Harrisonia, and Cneorum and possibly other members of this clade also lack gland dots. Harrisonia has a more syncarpous gynoecium than in Simaroubaceae. Other aspects of Harrisonia are somewhat characteristic of Rutaceae, such as its color on drying and its thorns.
In the study of five collections each of Cneorum pulverulentum and C. tricoccum, and two of C. trimerum, the second author has observed glandlike structures in some of the leaf blades of each species, but in being opaque, very irregular in distribution on the blade, and irregular in shape (mostly ± isodiametric but some considerably longer than wide) they are quite unlike those seen in Rutaceae (see discussion paragraph following the description of Rutaceae in this volume) and are probably not oil glands.
More traditionally, Cneoraceae s.str. consists of the single genus Cneorum Linnaeus, comprising three species: C. tricoccum Linnaeus, native of the NW Mediterranean region; C. pulverulentum Ventenat, of the Canary Islands; and C. trimerum (Urban) Chodat, of Cuba.
Chen Pangyu. 1997. Harrisonia. In: Chen Shukun, ed., Fl. Reipubl. Popularis Sin. 43(3): 15-16.