Family Antoniaceae

Antoniaceae (Endl.) J.G. Agardh

~ Loganiaceae sensu lato, Strychnaceae

Habit and leaf form. Small to large trees, or shrubs, or lianas; non-laticiferous and without coloured juice. Self supporting, or climbing. Mesophytic. Leaves opposite; petiolate; connate, or not connate; simple. Lamina entire; pinnately veined; cross-venulate. Leaves stipulate (in the form of a short sheath), or exstipulate (then the stipules represented by a ciliolate rim, or an interpetiolar line). Stipules interpetiolar; with colleters (often), or without colleters. Lamina margins entire, or dentate. Leaves without a persistent basal meristem.

Leaf anatomy. Hairs present, or absent; when present, eglandular. Complex hairs absent (glabrous or with simple hairs).

Stem anatomy. Internal phloem present. Secondary thickening anomalous; from a single cambial ring. ‘Included’ phloem present. Xylem with tracheids (abundant, in Usteria), or without tracheids; with fibre tracheids (Usteria), or without fibre tracheids (the rest); with libriform fibres (mostly), or without libriform fibres (Usteria). Vessel end-walls oblique; simple. Vessels with vestured pits. Primary medullary rays narrow (usually), or wide (Usteria). Tile cells present (e.g., Usteria), or absent. Wood diffuse porous; not storied; parenchyma apotracheal (mostly), or apotracheal and paratracheal (Usteria).

Reproductive type, pollination. Plants hermaphrodite; homostylous.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in cymes, or in panicles. The ultimate inflorescence unit cymose. Inflorescences terminal (usually), or terminal and axillary (Norrisia); several to many flowered, repeatedly dichasially branched to thyrsoid. Flowers bracteate; bracteolate; regular to somewhat irregular (usually regular except for the sometimes unequal sepals), or very irregular (Usteria); of Usteria zygomorphic. The floral irregularity involving the perianth, or involving the perianth and involving the androecium. Flowers 5 merous (usually), or 4 merous (Usteria); cyclic; tetracyclic. Free hypanthium absent. Hypogynous disk small or absent.

Perianth with distinct calyx and corolla; 8–10; 2 whorled; isomerous. Calyx 4–5; 1 whorled; polysepalous, or gamosepalous; unequal but not bilabiate (having one lobe enlarged or petaloid), or regular; persistent; non-accrescent; imbricate, or valvate, or open in bud. Corolla 4 (Usteria), or 5 (usually); 1 whorled; gamopetalous (usually hairy inside). Corolla lobes markedly shorter than the tube, or about the same length as the tube. Corolla valvate; hypocrateriform, or tubular (the tube often slender); regular; white (or cream), or yellow, or pink, or purple, or blue (or violet, or mauve); fleshy, or not fleshy.

Androecium 5 (usually), or 1 (Usteria). Androecial members adnate (inserted at the mouth of the corolla tube); all equal; free of one another; 1 whorled. Androecium exclusively of fertile stamens. Stamens 5 (usually), or 1 (Usteria); inserted in the throat of the corolla tube; reduced in number relative to the adjacent perianth (Usteria), or isomerous with the perianth; oppositisepalous (the single stamen of Usteria inserted between the larger pair of corolla lobes); alternating with the corolla members. Anthers dorsifixed; dehiscing via longitudinal slits; latrorse, or introrse. Pollen grains aperturate; 3 aperturate; colporate.

Gynoecium 2 carpelled. Carpels reduced in number relative to the perianth. The pistil 2 celled. Gynoecium syncarpous; eu-syncarpous; superior (nearly always), or partly inferior (rarely). Ovary 2 locular. Gynoecium stylate. Styles 1 (deciduous or persistent); apical. Stigmas 1 (unbranched); 1 lobed, or 2 lobed. Placentation axile (the placental stalk central). Ovules 15–50 per locule (‘many’); anatropous, or amphitropous; tenuinucellate.

Fruit non-fleshy; dehiscent; a capsule. Capsules septicidal. Fruit 1–50 seeded (to ‘many’). Seeds endospermic (the endosperm fleshy or starchy); winged (the wing diaphanous, reticulate-veined). Embryo straight, or curved.

Physiology, biochemistry. Alkaloids absent (or only traces present). Iridoids not detected. Verbascosides not detected. Cornoside not detected. Aluminium accumulation demonstrated (in Antonia ovata).

Geography, cytology. Tropical. ‘Tropics’. 2n= 22 (only Usteria screened. Supposed basic chromosome number of family: 11. Ploidy levels recorded: 2.

Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Gentianiflorae; Gentianales. Cronquist’s Subclass Asteridae; Gentianales. APG (1998) Eudicot; core Eudicot; Asterid; Euasterid I. APG 3 (2009) Order: Gentianales (?).

Species 8. Genera 4; Antonia, Bonyunia, Norrisia, Usteria.

Leeuwenberg 1980, under Loganiaceae. Associated with Strychnaceae via cladistic analyses by Struwe et al (1994), but nearer Gentianaceae in terms of this description. See comments under Loganiaceae.

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