The families of flowering plants.                                                                                                                                                                

Avicenniaceae Endl. ex Schnizl.



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~Acanthaceae, Verbenaceae

Habit and leaf form. Small mangrove trees and shrubs (branchlets articulate). Helophytic. Leaves opposite (decussate); leathery; simple. Lamina entire. Leaves exstipulate.

Leaf anatomy. Stomata diacytic.

Adaxial hypodermis present.

Stem anatomy. Internal phloem present. Secondary thickening anomalous; via concentric cambia. ‘Included’ phloem present. Xylem with libriform fibres. Vessel end-walls simple. Vessels without vestured pits. Wood parenchyma apotracheal.

Reproductive type, pollination. Plants hermaphrodite; viviparous.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in cymes, in panicles, and in umbels. The ultimate inflorescence unit cymose. Inflorescences terminal and axillary; cymose or thyrsiform, condensed or spiciform. Flowers bracteate; small; regular; cyclic; tetracyclic.

Perianth with distinct calyx and corolla; 9; 2 whorled; anisomerous. Calyx 5; 1 whorled; gamosepalous. Calyx lobes about the same length as the tube. Degree of gamosepaly (maximum length joined/total calyx length) about 0.5. Calyx slightly bilabiate; imbricate. Corolla 4; 1 whorled; gamopetalous. Corolla lobes about the same length as the tube, or markedly longer than the tube. Corolla imbricate; rotate, or campanulate; regular; yellow.

Androecium 4. Androecial members adnate (in the throat of the corolla); all equal to markedly unequal; free of one another; 1 whorled. Androecium exclusively of fertile stamens. Stamens 4; inserted in the throat of the corolla tube; didynamous (slightly), or not didynamous, not tetradynamous; isomerous with the perianth; oppositisepalous; alternating with the corolla members; filantherous to with sessile anthers. Anthers dehiscing via longitudinal slits; tetrasporangiate. Microsporogenesis simultaneous. Anther wall initially with more than one middle layer (up to three in A. officinalis). Tapetum glandular. Pollen grains aperturate; (2–)3 aperturate; colporate (colporoidate); 2-celled.

Gynoecium 2 carpelled. Carpels reduced in number relative to the perianth. The pistil imperfectly 4 celled. Gynoecium syncarpous; synstylovarious; superior. Ovary 2 locular. Locules partially secondarily divided by ‘false septa’. Styles 1. Ovules 2 per locule (one per locellus); pendulous; orthotropous to hemianatropous (the curvature arrested early, the ovule remaining almost orthotropous); unitegmic (but with incomplete growth of the integument, which does not form a micropyle); tenuinucellate. Endothelium not differentiated. Embryo-sac development Polygonum-type. Antipodal cells not formed (the 3 nuclei soon degenerating). Synergids hooked. Endosperm formation cellular. Endosperm haustoria present; chalazal and micropylar (of few cells). Embryogeny onagrad.

Fruit non-fleshy; dehiscent; a capsule. Capsules valvular (bivalved). Cotyledons 2. Embryo chlorophyllous.

Physiology, biochemistry. Not cyanogenic. Iridoids detected; ‘Route II’ type (normal and decarb.). Proanthocyanidins absent. Flavonols absent. Ellagic acid absent. C3. C3 physiology recorded directly in Avicennia. Anatomy non-C4 type (Avicennia).

Peculiar feature. Mangroves.

Geography, cytology. Tropical. Tropical coasts.

Taxonomy.Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Lamiiflorae; Lamiales. Cronquist’s Subclass Asteridae; Lamiales. APG 3 core angiosperms; core eudicot; Superorder Asteranae; lamiid; Order Lamiales (as a synonym of Acanthaceae?).

Species 11. Genera 1; only genus, Avicennia.