Family Alangiaceae

Alangiaceae DC.

Including Metteniusaceae Karst.

Habit and leaf form. Trees, or shrubs (sometimes spiny), or lianas (occasionally); laticiferous. Self supporting, or climbing (occasionally). Leaves alternate; spiral; petiolate; non-sheathing; gland-dotted, or not gland-dotted; simple. Lamina sometimes dissected (lobed), or entire; pinnately veined, or palmately veined; cross-venulate. Leaves exstipulate. Domatia occurring in the family (in several species); manifested as pits.

General anatomy. Plants with laticifers, or without laticifers (? — not mentioned by Metcalfe and Chalk).

Leaf anatomy. Stomata present; usually anomocytic. Hairs present, or absent (? sometimes with unequally 2–armed hairs).

Lamina dorsiventral, or isobilateral, or centric.

Stem anatomy. Secretory cavities present (?). Nodes tri-lacunar. Secondary thickening developing from a conventional cambial ring. Xylem with libriform fibres; with vessels. Vessel end-walls oblique; scalariform, or simple. Wood parenchyma apotracheal (diffuse).

Reproductive type, pollination. Plants hermaphrodite, or dioecious (in Madagascar).

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’ (with articulated pedicels); in cymes. The ultimate inflorescence unit cymose. Inflorescences axillary; cymes. Flowers regular.

Perianth with distinct calyx and corolla; 8–20; 1 whorled, or 2 whorled; isomerous, or anisomerous. Calyx 4–10 (or obsolete); 1 whorled; gamosepalous; entire, or lobulate, or blunt-lobed, or toothed. Calyx lobes markedly shorter than the tube. Degree of gamosepaly (maximum length joined/total calyx length) 0.75–1. Calyx regular (the lobes lanceolate or truncate). Corolla 4–10, or 5; 1 whorled; polypetalous, or gamopetalous (the reflexing, linear petals sometimes basally coherent). Corolla lobes when gamopetalous, markedly longer than the tube. Corolla valvate.

Androecium 4–40. Androecial members free of the perianth, or adnate, or free of the perianth and adnate; free of one another; 1 whorled. Androecium exclusively of fertile stamens. Stamens 4–40; isomerous with the perianth, or diplostemonous to polystemonous. Filaments not appendiculate. Anthers dorsifixed (rarely), or basifixed; when dorsifixed versatile, or non-versatile; introrse; tetrasporangiate. Endothecium developing fibrous thickenings. The initial microspore tetrads isobilateral. Anther wall initially with one middle layer. Tapetum glandular (?). Pollen grains aperturate; (2–)3–4(–8) aperturate; colpate, or porate, or colporate (colporoidate); 2-celled.

Gynoecium 2(–3) carpelled. The pistil 1 celled, or 2 celled. Gynoecium syncarpous (but often pseudomonomerous); eu-syncarpous; inferior. Ovary 1 locular, or 2 locular. Epigynous disk usually present (covering the top of the ovary), or absent. Styles 1. Stigmas 1; 1–3 lobed; truncate, or clavate. Placentation when unilocular apical; when bilocular apical. Ovules in the single cavity when unilocular, 1; 1 per locule; pendulous; with lateral raphe (and lateral micropyle), or with lateral raphe to with dorsal raphe; anatropous; unitegmic (Davis), or bitegmic (? - according to Hutchinson, who uses this feature in his key); crassinucellate. Embryo-sac development Polygonum-type. Polar nuclei fusing prior to fertilization. Antipodal cells formed, or not formed; proliferating (to 12 or more cells). Synergids pear-shaped. Hypostase present. Endosperm formation cellular, or nuclear.

Fruit fleshy; indehiscent; a drupe. The drupes with one stone (endocarp crustaceous or woody, one-seeded). Dispersal unit the fruit. Fruit 1 seeded. Seeds endospermic. Endosperm oily (and fleshy). Cotyledons 2 (foliaceous). Embryo chlorophyllous (1/1); straight.

Seedling. Germination phanerocotylar.

Physiology, biochemistry. Not cyanogenic. Alkaloids present, or absent. Iridoids detected; ‘Route I’ type (normal and seco). Proanthocyanidins absent. Ellagic acid absent. Saponins/sapogenins present. Aluminium accumulation not found.

Geography, cytology. Tropical. Alangium is represented in tropical Africa, Madagascar, China, SE Asia, Indo-malesia and SE Australia, while Metteniusa is restricted to NW tropical S. America. X = 11 (mainly), or 8 or 9.

Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Corniflorae; Cornales. Cronquist’s Subclass Rosidae; Cornales. APG (1998) Eudicot; core Eudicot; Asterid; unassigned to Euasterid I or Euasterid II. APG 3 (2009) Order: Garryales.

Species about 20. Genera 2; Alangium (about 17 species), Metteniusa (3 species).

This family exemplifies the well known difficulties in distributing certain Dicot families between Dahlgren’s Araliiflorae and Corniflorae. It is equally hard to assign them with confidence to the higher level groupings Crassinucelli and Tenuinucelli. This is interesting, given that the latter evidently represent a major divergence in the Dicot line of descent (cf.Young and Watson 1970, Chase et al. 1993).

Illustrations.
• Technical details: Alangium begonifolia.
• Alangium platanifolia: as Marlea begonifolia, Bot. Reg. XXIV, 61 (1838).

Support our developers