Meliaceae

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Meliaceae

Description

Trees, treelets, often pachycaul or, more rarely, shrubs or suckering shrublets, monopodial or sympodial, rarely with Terminalia-branching (Vavaea), dioecious, polygamous, monoecious or with all flowers hermaphrodite. Leaves exstipulate (occasionally pseudostipules present), spirally arranged, rarely decussate, pinnate (sometimes with a terminal ‘bud’, i.e. pseudogemmula), trifoliolate, with a single blade (simple or unifoliolate) or rarely bipinnate (Melia); rachis very rarely winged; leaflets usually entire, rarely lobed or serrate (or spinous, not in Malesia), sometimes with minute black glandular dots. Inflorescences thyrsoid, racemose or spicate, sometimes reduced to fascicles or solitary flowers, axillary, supra-axillary, ramiflorous, cauliflorous to groundlevel or rarely epiphyllous (Chisocheton). Flowershermaphrodite and/or more usually, unisexual, with well developed rudiments of opposite sex. Petals 3–7(-14), in 1 whorl, rarely (some Chisocheton species) in a spiral to give up to 2 (apparent) whorls, green, white, cream, pink to claret and violet or yellow (Aglaia). Stamens usually partially or completely united by a tube with or without lobes; anthers 3–10(-30) in 1 or, rarely, 2 or more whorls, sometimes locellate, at tips of filaments or at the margin of the tube or within its throat. Ovary (l–)2–6(-20)-locular, each locule with 1-many ovules; stylehead discoid to capitate. Fruit a capsule, berry or drupe. The seeds of Meliaceae are some of the most diverse and intricate in structure so far investigated. The following is largely taken from Cheek’s thesis (1989). The seeds are usually pendulous and epitropous in relation to the placenta. They are usually anatropous (but hemi-anatropous in most Turraeeae and Cipadessa), occasionally orthotropous as in all Chisocheton and some Guarea spp., campylotropous in e.g. Nymania (Turraeaeae), usually with a distinct funicle and raphe. Integument vascularization occurs in a few bitegmic genera, e.g. Chisocheton and Heynea (vascularized tegmen), Dysoxylum and Trichilia (vascularized testa) and is usual in pachychalazal seedcoats. In the Guareeae, arillate seeds characterize genera with bitegmic seeds, sarcotestal ones the unitegmic genera, while both conditions are found in Chisocheton and Dysoxylum, the genus with the greatest variation in seed anatomy investigated by Cheek. The single most taxonomically useful layer of the seedcoat in the majority of genera is the exotegmen: dimensions of the fibres and their wall characters but also the number of cell layers. However, in Dysoxylum, for example, the type of seed appendage and its organization are more helpful in recognizing species groupings as the exotegmen is reduced and poorly developed there. From his survey of the family, Cheek concludes that the ancestral meliaceous seed was comparatively large and bitegmic, with a small chalaza and a funicular-raphe-aril. From such can be derived the unitegmic sarcotestal state and the unitegmic ‘pseudoarillate’ state seen in Malesian species. Seed with fleshy aril or sarcotesta or a combination of these or winged and then attached to a woody columella, or with corky outer layers, or very rarely without any of them, endosperm usually absent; cotyledons collateral, superposed or, rarely, oblique, emergent or not at germination, when scale leaves are sometimes produced before first foliage leaves, which may be opposite or spirally arranged, simple or pinnate with later ones simple to bipinnate.

Distribution

Africa: present Asia-Tropical:, Malaya (Peninsular Malaysiapresent) Throughout the Tropics and Subtropics, with weak penetration into temperate zones: present
Throughout the Tropics and Subtropics, with weak penetration into temperate zones, the family comprises 50–52 genera with about 550 species.

Since Pennington & Styles’s generic monograph (1975), Megaphyllaea Hemsl. is considered to belong in Chisocheton Blume and Pseudocarapa Hemsl. in Dysoxylum Blume, while Heynea Roxb. ex Sims is considered distinct from Trichilia L. and Pseudoclausena T.P. Clark has been segregated from Walsura Roxb.; Turraea breviflora may represent an undescribed genus and Naregamia Wight & Arn. may not be generically distinct from Turraea L., nor may Pseudobersama Verdc. from Trichilia L.

The family is best represented in the Malesian region for, although Africa is almost as diversified in terms of the number of genera, the Malay Peninsula alone has more species (91 in 17 genera) than the whole of Africa (84 species) and, furthermore, begins to approach the specific richness of the whole neotropical region (122), where only eight genera are found, so that the Malesian region is over twice as rich in genera and almost as much so in species as the Neotropics. The largest genus, Aglaia, is centred on Malesia, the great bulk of the rest of the species being in the closely interrelated genera Dysoxylum and Chisocheton.

Pollination

Most species appear to be insect-pollinated, the agents possibly being bees, stingless sweatbees or syrphids in those cases examined (Aglaia spp., Xylocarpus spp.), while some species are strongly scented particularly in the evening, which, with their white flowers, suggests moth pollination in e.g. Chisocheton and Dysoxylum spp. as recorded in neotropical Cedrela and Guarea spp. Some species of these two Old World genera have long flagelliform inflorescences suggesting bat pollination, though the Bornean species are known to be visited by spiderhunters; whether these birds are efficacious pollinators is not known.

Dispersal

The fruits of species of Swietenioideae are dry dehiscent capsules, the winged seeds of Toona and Chukrasia being wind-dispersed, the irregular corky-coated ones of Xylocarpus being dispersed by saltwater in which they float just below the surface. The indehiscent fleshy fruits of Azadirachta indica are known to be dispersed by bats and baboons in Africa, those of Melia azedarach by birds.

Those species of Aglaia, Chisocheton, Dysoxylum (see Whittaker & Turner 1994) and Aphanamixis with dehiscent capsules and arillate or otherwise fleshy seeds are known to be taken by birds, apparently attracted by the contrasting colours of seeds and/or pericarp, while those species with indehiscent fruits are, at least in Aglaia and Reinwardtiodendron, eaten by primates which pass the seed divested of its fleshy layers (Pannell & Koziol 1987). The bird and primate ‘syndromes’ are associated in a sample of Aglaia spp. at least, with characteristic chemistry as might be expected, those taken by birds being high in lipid, those by primates higher in free carbohydrates, but it is clear that few if any tree species is restricted to any one species, or indeed group, of vertebrate dispersers. Moreover, as there are no native primates in some parts of the ranges of certain species, Aglaia elaeagnoidea in New Caledonia for example, it must be concluded that bats or birds are active dispersal-agents even for those species which are thought to be dispersed by primates or other terrestrial mammals elsewhere. The seeds of many species are taken by squirrels but whether these animals do more than harm is unknown. For further details on Aglaia, see below. A parallel to the situation within Aglaia appears to be bird-dispersed Heynea and the closely allied but mammal-dispersed Walsura (Clark & Mabberley 1991). In New Guinea, birds of paradise are the only known dispersal agents for Chisocheton lasiocarpus (‘C. weinlandii’) seeds (Beehler 1983).

Seeds of Dysoxylum angustifolium, and possibly Sandoricum borneense, are believed to be dispersed by fish like those of the neotropical Guarea guidonia (L.) Sleumer (Pennington 1981). This ‘syndrome’ has yet to be analysed chemically.

Cytology

There is a wide range of somatic chromosome numbers from 2n = 16 (Sandoricum koetjape) to c. 360 in some African Trichilia spp., with polyploid series in some genera, e.g. Aphanamixis and Aglaia and within species, e.g. Chisocheton cumingianus. Much is summarized by Khosla & Styles (1975) and Styles & Khosla (1976) with further discussion by Datta & Samanta (1977) and counts for Aglaia provided by Pannell (1992) and Chisocheton by Mabberley (1979). 2n = 16-c. 360.

Phytochemo

Meliaceae belong to Rutales s. str. comprising Rutaceae, Meliaceae, Simaroubaceae, Cneoraceae and Burseraceae (Waterman & Grundon 1983). A chemical key character of this order (if Burseraceae are excluded) is the synthesis and accumulation of bitter and biologically active nortriterpenoids called limonoids, meliacins and quassinoids depending on structural features and occurrence. These oligonortriterpenoids derive from tetracyclic triterpenes which are known as protolimonoids. Moreover, each family of this order has its own main patterns of secondary metabolites. Recently, Meliaceae have interested many phytochemists and biologists, because they yield many compounds with insect-antifeeding, insect-repellent or/and insecticidal properties, and because many members of this family are highly esteemed in traditional medicine of most continents.

A number of phytochemical review treatments of Meliaceae are available in recent literature, e.g. Hegnauer 1969, 1983, 1990; Waterman & Grundon 1983. Furthermore, many reviews are devoted to the chemically complex limonoids, which in the case of Meliaceae are sometimes called meliacins; see e.g. Arnason et al. 1989, 1993; Champagne et al. 1992; Ley et al. 1993; Rembold 1983, 1989; Rembold & Puhlman 1993; Saxena 1989; Taylor 1983; Triterpenes 1984–1994.

References alluded to in the above reviews are only exceptionally repeated in the following phytochemical survey in which metabolites of Meliaceae are arranged following Hegnauer (1983).
1. R. Hegnauer

Citation

Mabb. - in Fl. Nouv.-Caléd. et Dép. 1988: 17–89
T.D.Penn. & Styles - in Blumea. 1975: 419–540
Mabb. & Pannell - in Tree Fl. Malaya. 1989