120 * ACANTHACEAE ¹

Marco F Duretto ²

Herbs (Tas.) or shrubs, rarely climbers or small trees; branches often longitudinally grooved or angled. Leaves opposite and decussate, simple or compound, margins entire or shortly toothed, or rarely spiny and deeply incised, often with cystoliths (these detected with a hand lens if the leaf is held against a strong light, where they appear as white streaks). Inflorescences axillary or terminal, a spike (Tas.), cyme or racemes or flowers solitary, often with both chasmogamous and cleistogamous flowers; flowers often clustered, frequently in axil of a bract and with 2 leafy bracteoles. Flowers bisexual, usually zygomorphic, 4–5-merous. Calyx segments usually 5, equal and fused only at base, rarely 4 or 8–20-lobed or unequal and fused to a greater degree. Corolla tubular; lobes 5, ± equal or 2-lobed. Stamens epipetalous, 2 or 4 fertile, sometimes with 2 staminodes; filaments free or basally fused in pairs; anthers 2-locular, dehiscing by longitudinal slits. Ovary superior, 2-locular, 2–12 ovules per loculus; style terminal. Fruit a loculicidal capsule, often opening explosively after drying or on contact with water, usually with seed-bearing hooks (jaculators) that persist after the seeds have been ejected; seeds 2-many, usually compressed and discoid, with or without mucilaginous hairs, usually without endosperm.

A family of about 2500 species in 250 genera found chiefly of tropical regions. In Australia there are about 30 genera and 60 species (both native and introduced) with representatives in all States and mainland Territories. In Australia native species are found mostly in tropical and subtropical regions and 3 genera are restricted to arid and semi-arid areas. The family is placed in the Lamiales. A number of species are cultivated as ornamentals for their showy flowers and/or bracteoles.

Synonymy: Avicenniaceae.

Key reference: Barker (1986).

External resources: accepted names with synonymy & distribution in Australia (APC); author & publication abbreviations (IPNI); mapping (AVH, NVA); nomenclature (APNI, IPNI).

1 * ACANTHUS

Acanthus L., Sp. Pl. 2: 639 (1753).

Perennial herbs or shrubs. Leaves in a large radical rosette, variously lobed, generally spiny. Inflorescence terminal, a long spike; bracts leaf-like, spiny. Calyx 4-lobed, the upper and lower lobes large, the lateral lobes small. Corolla with a short tube and relatively large 3-lobed lower lip, no upper lip developed. Stamens 4, didynamous, shorter than corolla; filaments angled; anthers unilocular, connivent in pairs. Style filiform; stigma shortly bifid. Fruit with jaculators well developed.

A genus of more than 30 species indigenous to the Mediterranean region, Africa, tropical Asia and northern Australia. The two species indigenous to northern Australia, A. ilicifolius L. and A. ebracteatus Vahl, are mangroves. Several species are cultivated in gardens and can persist or become weedy.

1 * Acanthus mollis L., Sp. Pl. 2: 639 (1753)

Bear’s-breeches

Acanthus cf. mollis sensu R.Barker, J. Adelaide Bot. Gard. 9: 74 (1986).

Illustrations: Spencer, Horticultural Flora of South-eastern Australia 3: 283 (2002); Richardson et al., Weeds of the South-East, an Identification Guide for Australia 85 (2006).

A robust perennial herb. Leaves in a large basal rosette; first-formed leaves with petiole about as long as the lamina; lamina 30–60 cm. long, 20–30 cm broad, oblong-ovate in outline, deeply pinnately lobed or compound with very large pinnate upper lobe and 1 or 2 small leaflets below; lobes also cut and with large irregular teeth; adaxial surface bright green, shining, with veins slightly impressed, becoming glabrous; abaxial surface paler with veins puberulent; rachis puberulent. Inflorescence a large, erect, terminal spike, 60–120 cm high; bracts 3–4 cm long, ovate, spinous-dentate, bracteoles 2, narrow-linear, pungent. Calyx with an upper lobe 4–5 cm long, a lower lobe slightly smaller and with 2 very small lateral lobes. Corolla white or pale pink, sometimes with purple veins, larger than calyx, the 3-lobed lower lobe projecting beyond the calyx, the basal tube c. 4 mm long, and having a ring of hairs below the insertion of the stamens and covering the top of the ovary. Ovary superior, sessile on a nectar-secreting disk, bilocular with large axile placenta; ovules 2 in each loculus; seeds lenticular, 12–14 mm long, c. 8 mm broad. Flowering Jun.–Jan.; fruiting Jan.?–Jun.

Tas. (FUR, TNS, TSE); also naturalised in SA, Qld, NSW?, Vic.; native in S Europe. Recorded from near Wynyard, George Town and the Hobart area and possibly more widespread. Introduced as a garden-plant and persisting or becoming naturalised in wet and/or shaded sites, usually where formerly cultivated or nearby. Barker (1986) indicates that what is being called A. mollis in Australia may be an intermediate between A. mollis and A. spinosus L. and so lists what is found in this country as A. cf. mollis.

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