| # The Families of Angiosperms |

L. Watson and M.J. Dallwitz

### Avicenniaceae Endl. ex Schnizl.

~ Verbenaceae, Acanthaceae-Avicennioideae.

Habit and leaf form. Small mangrove trees and shrubs (with articulate branchlets and conspicuous aerial prop-roots and pneumatophores). Helophytic. Leaves opposite (decussate); leathery; simple. Lamina entire. Leaves exstipulate.

Leaf anatomy. Stomata diacytic. Adaxial hypodermis present.

Axial (stem, wood) anatomy. Primary vascular tissues in a cylinder, without separate bundles, or comprising a ring of bundles, or comprising two or more rings of bundles; collateral. Internal phloem present (but transient), or absent. Secondary thickening developing from a conventional cambial ring, or anomalous. The anomalous secondary thickening when present, via concentric cambia.

The vessel end-walls simple. The vessels without vestured pits. The axial xylem with libriform fibres; including septate fibres (these thick-walled). The parenchyma apotracheal. ‘Included’ phloem present.

Reproductive type, pollination. Unisexual flowers absent. Plants hermaphrodite; viviparous.

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in cymes, in panicles, and in umbels. The ultimate inflorescence units 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, phytochemistry. C3. C3 physiology recorded directly in Avicennia. Anatomy non-C4 type (Avicennia). Not cyanogenic. Iridoids detected; ‘Route II’ type (normal and decarb.). Proanthocyanidins absent. Flavonols absent. Ellagic acid absent.

Special distinguishing feature. Mangroves.

Geography, cytology. Tropical. Tropical coasts.

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

Species 11. Genera 1; only genus, Avicennia.

General remarks. Differing conspicuously from Acanthaceae in the regular corolla, 4-celled ovary with secondary septa, the differently orientated ovules with conventional funicles, and valvular capsule dehiscence. Records relying on limited sampling show further differences in anther wall development and embryology.

Illustrations. • Avicennia germinans: Standley et al., Flora of Guatemala 2 (1970). • Avicennia officinalis: Nat. Pflanzenfam. IV (1897). • Avicennia officinalis, embryology: Nat. Pflanzenfam. IV (1897). • Foliar hairs of Avicennia nitida, with Clerodendron and Petraea (Verbenaceae) and Pityrodia (Dicrastylidaceae) (Solereder, 1908).

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, genera included in each family, and classifications (Dahlgren; Dahlgren, Clifford, and Yeo; Cronquist; APG). See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 8th June 2026. delta-intkey.com’.

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