Shrubs or small trees, or less commonly medium-sized to tall trees. Leaves verticillate in alternate whorls of 3 or 4, occasionally 5, simple, margin entire or crenate-serrate; Stipules interpetiolar, the number per node equal to the number of petioles or rarely otherwise, simple, narrowly triangular, caducous. Inflorescences axillary and solitary or two subunits serially inserted, or less commonly terminal, paniculate, with branching at proximal nodes whorled and at peripheral nodes less regular and ± alternate, many-flowered, with peduncles up to half of total length, the axes bearing small caducous bracts at nodes. Flowers bisexual, 4-5(-6)-merous, apetalous, pedicellate. Sepals valvate, subcoriaceous, connate at base for 1/4-1/2 of their length. Stamens with filaments subulate, glabrous and anthers broadly cordate, retuse at apex and incised at base. Ovary superior, ± apocarpous, with 2-5 carpels, frequently not all maturing to fruiting stage; Fruit multiple, a follicetum with 2-5 free follicle-like fruitlets attached to receptacle at base and each dehiscing along the full length of the adaxial suture, the valves boat-shaped, stiff-coriaceous, their margins minutely thickened, the styles and calyx persistent. Seeds 1-4 per carpel, oblong, glabrous, with a lateral to terminal wing.
Asia-Tropical: Bismarck Archipelago (Bismarck Archipelago present); Maluku (Maluku present); New Guinea present, NE Australia present, New Caledonia present, Pacific: Fiji (Fiji present), Solomon Islands absent, Vanuatu absent
16 species; from Fiji (1 species), New Caledonia (10 species) and NE Australia (1 species) to Malesia: Moluccas and New Guinea; absent from the Bismarck Archipelago, Solomon Islands and Vanuatu.
2. In several Malesian species the leaves vary from small, coriaceous and sometimes bullate to larger, papyraceous and flat. This is probably related to habitat and exposure, and all Malesian species occur over a considerable altitudinal range. 5. The number of stipules per node is typically equal to the number of leaves although in A. davidsonii (F. Muell.) Hoogland in Australia it is sometimes twice the number of leaves (R.W. Barnes, pers. comm.). 3. The inflorescences are generally shorter than in most other Malesian genera, and flowering is often profuse. The flowers are fragrant and usually described as pale, varying from white, greenish cream to yellowish, the calyx being cream, yellow, yellow-green or rarely reddish (flowers old?), the filaments yellow or white and the stigmas white. The buds vary from creamy white to pale yellowish green. Young fruits are green or reddish, and mature, dehisced fruitlets are brown. Young leaves are sometimes pink. 1 Distinguished immediately from Spiraeanthemum, which in Malesia has been found only in the Bismarck Archipelago (New Britain and New Ireland), by the verticillate leaves. The only other genus in Malesia in which verticillate leaves regularly occur is Pullea, which is easily recognised in flower or fruit by the half-inferior ovary and imbricate calyx lobes. Only in a single Malesian case, in Acsmithia reticulata, have opposite and verticillate leaves both been found within the same individual, but here the opposite, as well as ± alternate, leaves are suspected to be teratological. 4. Venation. In the Malesian species there are comparatively few lateral veins per leaf, commonly c. 5, opposite or alternate, on each side of the midrib. The main lateral veins form an acute acroscopic angle with the midrib, and in addition, sometimes there are much weaker veins ± at right angles to midrib in between prominent laterals or arising near their base. The midrib is sometimes not completely straight towards the apex. 6. Species delimitation in Malesia is not straightforward and the key relies in part on characters that are difficult to observe (e.g. ovule number).
U.S. Explor. Exped. - in Phan. June 1854: et Atlas (1865) t. 83 B: specie lectotypica exclusa; et sensu: Schltr., Bot. Jahrb. Syst. 52 (1914) 139
Engl. - in Nat. Pflanzenfam., ed. 2. 1928: 237
Hutch. - in Gen. Flow. Pl. Dicot. 1967: 8
Hoogland, Fl. Nouv.-Caléd. m.s.: at P.
A.C. Sm. - in J. Arnold Arbor. 1952: 139