Chisocheton

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Chisocheton

Description

Trees pachycaul to leptocaul, unbranched or, usually, with sympodial crown, sometimes laticiferous or myrmecophilous, very rarely foetid, dioecious or polygamous. Leaves pinnate and pseudogemmulate or imparipinnate, very rarely paripinnate, to 2.4 m long; leaflets in 2–29 pairs. Inflorescence paniculate to thyrsoid or with long peduncle and congested racemose, axillary to supra-axillary, ramiftorous or rarely borne on congested cauliflorous branches, or epiphyllous (New Guinea). Flowers articulated with pedicel or inflorescence branches, sometimes with elongated receptacle (pseudopedicel). Petals (3–)4–6(–14) in 1 (or 2) whorls, free, imbricate, quincuncial or alternative, often merely at apices, or valvate, rarely weakly united below or with base of staminal tube. Staminal tube cylindrical, sometimes weakly expanded or contracted at the mouth, margin entire, crenate or with 4–10(–30) emarginate, truncate or narrowly lanceolate 2- (or 3-)fid lobes; anthers (3–)4–10(–30), usually attached within the tube, alternating with lobes, usually locellate. Ovary 2–8-locular, each locule with 1 or 2 collateral or superposed orthotropus ovules; stylehead clavate or discoid. Fruit a 2–5(–8)-valved loculicidal capsule, the valves 1– (or 2–)seeded; pericarp usually leathery or almost completely lignified, sometimes laticiferous. Seeds obovoid-spheroid to scutelliform or orange-segment- shaped, variously arillate or sarcotestal, orthotropous; hilum often large and heavily vascularized, whitish; aril reddish orange with ± free flap over black testa; sarcotesta red, tough; cotyledons collateral, oblique or superposed.

Distribution

New Hebrides present, continental Asia present, from Assam and tropical China throughout Malesia SE- wards to northern Queensland and the New Hebrides present
50 speciesfrom Assam and tropical China throughout Malesia SE- wards to northern Queensland and the New Hebrides. Of the 46 in Malesia, all but 5 are endemic; three species are found only in continental Asia and one in the New Hebrides

Morphology

From a consideration of the distributions and relationships of Chisocheton species occurring in southern Malaya, Corner considered the flora of the Sedili region to have been derived from the China Sea rivers of the glacial period. Whitmore , who illustrated the distribution of species according to Mabberley’s monograph, considered the genus to be Sundaic in origin and to have spread to East Malesia. Mabberley showed how the most pachycaul species of particular alliances are very restricted in distribution compared with their leptocaul allies, a conclusion to be predicted from Corner’s Durian Theory. The pseudogemmulate leaves with their indeterminate growth have attracted considerable morphological attention (see Mabb., l.c., for a summary) as have the epiphyllous species . Within the genus, there are species with imparipinnate leaves, paripinnate leaves (some forms of C. patens), but the majority have the leaf terminated by a pseudogemmula, which is a crozier-like bud of undeveloped leaflets, from which leaflets unfold at intervals. As in Guarea , the only other genus in which this occurs, some species are intermediate between the truly pseudogemmulate and the imparipinnate in that all the leaflets that will develop are produced in one flush, though the most apical may be tardy in expanding. Such is a cornmon state of affairs in some species of Dysoxylum (q. v.). Inflorescences are borne in axillary, supra-axillary or ramiflorous positions. In each of these places and also on the bole, the inflorescences may be borne on dwarf shoots with reduced leaves. Such shoots are also known in Melia (q.v.), where they continue growth after fruit set. The epiphyllous inflorescences are borne on the adaxial surface of the leaf rachis, their vascular supplies being connected directly with that of the adjacent rachis, there being no adnation or other ‘fusion’. In C. tenuis, there are also vegetative buds, their origin like that of the epiphyllous inflorescences in this species and C. pohlianus being considered heterotopic or, indeed, homoeotic. Notes.

Uses

Locally, wood is used for construction but is not especially sought after.

Citation

Mabb. 1979 – In: Bull. Brit. Mus. Nat. Hist, Bot.: 301.