Shrub, rarely attaining the size of a small tree, 1-3 (–5) m tall with pale branches. Pneumatophores 10-20 (—25) cm long. Leaves lanceolate to ovate-elliptic, coriaceous 3-8 cm long, 1.5-3.5 cm broad, very acute to acuminate, entire; glabrous and shining green above, whitish-tomentose beneath, turning somewhat blackish when dried; petiole short, 3-5 (—8) mm long, usually margined with a very narrow lamina. Flowers dingy yellow with somewhat orange throat, sessile, in heads at the apex of stout, angular peduncles and often with an opposite pair much down below on the same peduncle. Bract and 2 bracteoles concave, ovate to suborbicular, shorter than the sepals (except the bracts of the lowest flowers), ciliate; bract (2.5—) 3-4 mm long, 1.5-3 mm broad, acute; bracteole 2-3.5 mm long, 2-2.5 mm broad. Calyx 5-partite almost to the base, or sepals (3—) 3.5-4 mm long, 2.5-3 mm broad, broadly ovate to suborbicular, connate at the base, concave, obtuse, somewhat ciliate and tomentose on the back. Corolla c. 5 mm in diam., 5-6 mm long; tube very short; lobes 4, ovate, acute, subequal, slightly exceeding the calyx, c.1.5. mm in diam. Stamens 4, sub-sessile included, inserted at the mouth and alternating with corolla lobes. Ovary ellipsoid-linear, about as long as the tube of corolla, villous; style shorter than the ovary, 2-fid. Capsule broadly ellipsoid or ovoid, 12-18 mm long, 10-12 mm broad, compressed, ± apiculate, pale green or slightly greyish-tomentose; seed usually 1, large, often germinating on the plant (viviparous); embryo with plumule enlarged before falling.
Seed large, compressed, germinating within the fruit while still on the tree.
Usually a small evergreen tree 3–4 m tall, sometimes to 10(12) m tall, with a much-branched rounded crown and an extensive widely spreading horizontal root system, less often a shrub; roots, particularly in muddy places, giving rise to numerous erect pencil-like pneumatophores, 10–38 cm tall.
Trunk ± stout, up to c. 25 cm in diameter, sometimes with aerial ‘breathing’ roots (not reaching the ground) on the lower portion; bark smooth and somewhat powdery, whitish or yellow-green; branchlets decussate, slender, subterete or quadrangular, with a densely pulverulent (powdery)-puberulent whitish or greyish thin outer bark, nodes swollen.
Cotyledons reniform, light green.
Bracts and bracteoles 2–3 mm long, ovate to broadly ovate, concave, obtuse or rounded at the apex, ciliate, glabrous on the inner face, densely silvery-tomentose or sericeous on the outside, finally glabrescent, closely appressed to the calyx.
Cymes usually solitary in leaf axils towards the end of the branchlets, and usually with 3 at the apex of the branchlets, few- to many-flowered, capitate or subcapitate; the heads 7–15 mm in diameter; peduncles 0.6–4 cm long, quadrangular, sulcate when dry, densely thinly powdery-puberulent.
Leaves 3.5–12 × 1.3–5 cm, ovate or lanceolate to oblong-lanceolate or elliptic, acute or subacute at the apex, entire with margins slightly revolute, cuneate at the base or ± tapering into the petiole, glabrous or ± obscurely powdery on upper surface, densely pulverulent (powdery)-puberulent or felted-tomentellous on lower surface, coriaceous, usually light green on both surfaces or discolorous and silvery-greyish or greenish-yellow beneath, becoming dark olive-green to blackish above and sordid grey to yellowish beneath on drying; midrib slender and ± prominent on both surfaces, reticulation slightly raised above and obscured beneath; secondary nerves 8–15 on each side of midrib; petiole 3–14 mm long, flattened above, densely powdery-puberulent or tomentellous, rarely glabrescent.
Capsule 1.2–3 × 0.7–2 cm, subglobose, broadly ellipsoid or ovoid, somewhat asymmetric and abruptly tapering into a short narrow apical beak at least when young, yellowish or pale to greyish-green densely powdery-puberulent, the calyx and involucre persisting unchanged.
Filaments erect; anthers subequalling the filaments, suborbicular, sulphur-yellow, turning black.
Corolla white at first, turning yellow or orange to dark orange or reddish-orange, becoming blackish when dry, rigid, caducous; tube 1–2 mm long, glabrous; lobes 3–4 mm long, ovate, densely tomentellous or sericeous outside, glabrous inside.
Calyx green; lobes 2–4 mm long, ovate or broadly ovate to elliptic, rounded at the apex, densely tomentellous outside, fimbriate-ciliate on the margins, persistent.
Seed usually single, compressed.
Capsule subglobose, broadly ellipsoid or ovoid, usually not beaked when mature, 1.2–3 cm. long, 0.7–2.5 cm. wide, velvety scaly-tomentose.
Ovary yellow-green, narrowly conical, 2.5 mm. long, pubescent above, glabrous below; style 0.8 mm. long, glabrous, 2-fid.
Shrub or small tree 1–9 m. tall or even attaining 15 m. when left in favourable conditions; bark brownish yellow-green, smooth.
Pneumatophores 10–25(–40) cm. long. Stems finely grey-tomentose.
Leaf-blades elliptic or ovate-elliptic to elliptic-lanceolate, 3–12 cm. long, 1.5–5 cm. wide, acute to acuminate or even obtuse at the apex, cuneate at the base, green or yellow-green and glabrous above, minutely silvery grey or whitish tomentose beneath, glaucous, sometimes blackening on drying; petiole 3–8(–14) mm. long, gradually passing into the lamina.
Flowers in small dense heads 0.7–1.2 cm. diameter, with 3 heads per terminal inflorescence but lateral branches originating from lower leaflets or leafy nodes; sometimes a pair of additional opposite flowers borne on central peduncle well below the head; bracts and bracteoles ovate or ± round, concave, adpressed to calyx, 2–4 mm. long, 1.5–3 mm. wide, acute, ciliate.
Sepals ovate, elliptic or ± round, 3.5–4 mm. long, 2.5–3 mm. wide, obtuse, ± densely ciliate and tomentose outside.
Corolla yellow, apricot or dark orange, turning black; tube 2–3 mm. long, glabrous; lobes ovate, 2.5–4 mm. long, 2–3 mm. wide, pubescent outside.
Anthers sulphur-yellow turning black.
Often a small tree, 3 to 5 m in height, but it can reach 10 m, with a much-branched rounded crown; a common and often dominant constituent of mangrove swamps, but also away from the sea, encroaching back up the feeder streams, and growing on the banks of fresh water rivers. No prop or stilt roots are produced, but the underground root system is extensive and, in soft mud, throws up a forest of pencil-like pneumatophores, 15 to 38 cm long. The tree is a first colonizer of poor swamp land where little else will grow. Mud and silt accumulate among the pneumatophores and conditions become suitable for the establishment of the other mangroves, Ceriops and Rhizophora. In mangrove swamp forests Avicennia has usually been forced back to the landward side. Bark: yellowish-green, inclined to be powdery. Leaves: opposite, simple, ovate, lanceolate to elliptic, 3 to 10 x 1.2 to 4 cm, usually about 7 x 2.5 cm, without hairs, green above, pallid grey below; apex and base tapering; margin entire; petiole thickset, about 5 mm long. Flowers: white or cream to yellow, sweetly scented, small, in dense spherical terminal or axillary heads, or capitate cymes, on thickset square stalks, about 2 to 3 cm long. Bisexual; floral parts in fours to fives; corolla tube bell-shaped, rather shorter than 4 to 5 petal lobes, somewhat fleshy; stamens 4, enclosed within the tube; ovary 4-chambered. Fruit: a rather flattened capsule, about 2 to 2.5 cm in diameter, dehiscing by 2 valves (March to September).The seed germinates on the tree before it is liberated but, unlike the other mangroves, A. marina does not produce the torpedo-shaped hypocotyl; the fruits are frequently washed up on beaches.