Plants → Magnoliophyta → Magnoliopsida → Lamiales → Acanthaceae Juss. → Browse taxa…
Common name. Acanthus Family.
Habit and leaf form. Shrubs, or herbs, or trees (rarely). ‘Normal’ plants, or switch-plants (rarely). Leaves well developed (usually), or much reduced. The herbs annual to perennial; plants with a basal concentration of leaves, or with neither basal nor terminal concentrations of leaves. Self supporting (mostly, by contrast with Thunbergiaceae), or epiphytic, or climbing (sometimes, e.g Adhatoda); when climbing, stem twiners, or root climbers, or scrambling. The twiners twining clockwise. Trees leptocaul. Hydrophytic, or helophytic (including a few mangroves), or mesophytic (many in damp places in tropical forests), or xerophytic. Leaves opposite (decussate); gland-dotted, or not gland-dotted; simple. Leaf blades dissected, or entire; flat; pinnately veined; cross-venulate. Leaves without stipules. Leaf blade margins entire, or crenate, or serrate, or dentate; flat, or revolute, or involute. Domatia recorded (from 3 genera); represented by hair tufts. Stem anatomy. Nodes unilacunar. Secondary thickening developing from a conventional cambial ring. Roots. Aerial roots present, or absent.
Reproductive type, pollination. Fertile flowers hermaphrodite. Unisexual flowers absent. Plants hermaphrodite. Entomophilous. Pollination mechanism conspicuously specialized (commonly exhibiting a loose-pollen mechanism, cf. Scrophulariaceae etc. — e.g. the large bee-flowers of Acanthus), or unspecialized.
Inflorescence and flower features. Flowers solitary, or aggregated in ‘inflorescences’; in cymes, in racemes, and in verticils. The terminal inflorescence unit cymose (in about 75%), or racemose. Inflorescences commonly dichasial cymes, becoming monochasial in the ultimate branches, and frequently condensed in the leaf axils, cf. Labiatae; pseudanthial, or not pseudanthial. Flowers bracteate; bracteolate (the bracts and bracteoles often showy); somewhat irregular to very irregular (in about 75% of the genera), or regular; usually more or less zygomorphic. The floral asymmetry involving the perianth and involving the androecium. Flowers 4 merous, or 5 merous; tetracyclic. Free hypanthium absent. Hypogynous disk present. Perianth with distinct calyx and corolla; (6–)8, or 10; 2 -whorled; isomerous, or anisomerous. Calyx (3–)4, or 5; 1 -whorled; gamosepalous; entire, or lobed; variously lobulate, or blunt-lobed; imbricate, or valvate, or contorted, or open in bud. Degree of gamosepaly, maximum length joined/total calyx length 0.5–0.9. Calyx when K5, with the median member posterior. Corolla 4, or 5; 1 -whorled; gamopetalous (at least basally). Degree of gamopetaly 0.5–0.75. Corolla imbricate, or contorted, or with open aestivation (in Acanthus only); bilabiate, or unequal but not bilabiate (the upper lip sometimes suppressed). Androecium 2, or 4(–5). Androecial members adnate (usually exserted, the filaments inserted on the corolla tube); all equal, or markedly unequal; free of one another, or coherent; when coherent, 2 - adelphous (partially connate, in pairs); 1 -whorled. Androecium exclusively of fertile stamens, or including staminodes. Staminodes when present, 1–3. Stamens 4(–5), or 2; didynamous (in about 75% of the species), or not didynamous, not tetradynamous; reduced in number relative to the adjacent perianth, or isomerous with the perianth; oppositisepalous; all alternating with the corolla members. Anthers separate from one another, or connivent; dorsifixed (often with one lobe reduced or abortive); dehiscing via longitudinal slits; unilocular to bilocular; tetrasporangiate; appendaged (the connective often long, cf. Salvia), or unappendaged. Pollen shed as single grains. Gynoecium 2 carpelled. The pistil 2 celled. Gynoecium syncarpous; synstylovarious to eu-syncarpous; superior. Ovary plurilocular; 2 locular. Gynoecium median. Ovary sessile. Styles 1; attenuate from the ovary; apical; much longer than the ovary at anthesis (usually). Stigmas 2 (the posterior often smaller); dry type; non-papillate; Group II type. Placentation axile. Ovules 2–50 per locule (i.e., 2 to many); non-arillate, or arillate (occasionally exhibiting what may be a funicular aril - cf. Corner); anatropous to campylotropous.
Fruit and seed features. Fruit non-fleshy; dehiscent; a capsule. Capsules loculicidal. Fruit elastically dehiscent. Dispersal unit the seed. Seeds non-endospermic; borne on minute, hook-like outgrowths (‘retinacula’); conspicuously hairy, or not conspicuously hairy; with amyloid, or without amyloid. Embryo well differentiated. Cotyledons 2. Embryo achlorophyllous (3/3); large. Testa sometimes covered with hairs or scales which become sticky or slimy when wet. Seedling. Germination phanerocotylar.
Physiology, biochemistry. Aluminium accumulation not found. Photosynthetic pathway: C3, or C4.
Special features. The seeds on elongated, indurated, hook-shaped funicles (‘retinacula’). Mangroves (a few), or non-mangrove species.
Geography, cytology, number of species. Holarctic, Paleotropical, Neotropical, Cape, and Australian. World distribution: centred on Indomalaysia, Africa, Brazil and central America. X = 7–21. 2500 species.
Economic uses, etc. A few cultivated ornamentals: Acanthus, Aphelandra, Fittonia, Beloperone, Justicia etc.
TD Macfarlane, L Watson & NG Marchant
FloraBase is produced by the staff of the Western Australian Herbarium, Biodiversity and Conservation Science, Department of Biodiversity, Conservation and Attractions. Publication or other use of content on this site is unauthorised unless that use conforms with the copyright statement.
Western Australian Herbarium (1998–). FloraBase—the Western Australian Flora. Department of Biodiversity, Conservation and Attractions. https://florabase.dpaw.wa.gov.au/