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The families of flowering plants

L. Watson and M.J. Dallwitz

Acanthaceae Juss.

Including Justiciaceae Rafin., Thomandersiaceae Sreemadhavan; excluding Nelsoniaceae, Mendonciaceae, Thunbergiaceae.

Habit and leaf form. Shrubs, or herbs, or trees (rarely, but including a few mangroves). ‘Normal’ plants, or switch-plants (rarely). Leaves well developed (usually), or much reduced. The herbs annual to perennial; with a basal aggregation of leaves, or without conspicuous aggregations 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); flat; gland-dotted, or not gland-dotted; simple. Lamina dissected, or entire; pinnately veined; cross-venulate. Leaves exstipulate. Lamina margins entire, or crenate, or serrate, or dentate; flat, or revolute, or involute. Domatia occurring in the family (recorded in 3 genera); manifested as hair tufts.

Leaf anatomy. The leaf lamina dorsiventral (sometimes incompletely so), or bifacial (sometimes isobilateral in several genera); exhibiting epidermal salt glands (reported on both leaf surfaces in Acanthus ilicifolius), or without epidermal salt glands (usually, assuming that “glandular hairs” which are very widespread in the family are not concerned with salt secretion). Abaxial epidermis papillose, or not papillose. Mucilaginous epidermis absent. Stomata mainly confined to one surface (abaxial), or on both surfaces; diacytic (nearly always), or paracytic (recorded only for Lepidagathis). Hairs of diverse kinds present; eglandular, or glandular (the former mostly unicellular or uniseriate, the latter occurring throughout the family, mostly small and short-stalked); unicellular and multicellular. Unicellular hairs branched, or simple. Multicellular hairs branched, or simple. Adaxial hypodermis present (rarely), or absent. Lamina without secretory cavities. Cystoliths very commonly present (showing as streaks in the lamina), or absent (Acantheae, Aphelandreae). The mesophyll with sclerenchymatous idioblasts (as bundles of acicular fibres, supposedly peculiar to the family and recorded in numerous genera); containing crystals, or without crystals. The crystals raphides (rarely), or solitary-prismatic. Main veins embedded. Minor leaf veins with phloem transfer cells (Ruellia), or without phloem transfer cells (9 genera).

Axial (stem, wood) anatomy. Cork cambium present; initially deep-seated (sometimes), or initially superficial. Nodes unilacunar. Primary vascular tissues in a cylinder, without separate bundles; collateral, or bicollateral. Internal phloem present (noted as conspicuous groups in about 10 genera), or absent. Cortical bundles absent. Medullary bundles present (with groups of collateral and inversely orientated bundles in some Acanthus spp.), or absent. Secondary thickening developing from a conventional cambial ring (nearly always?), or absent (with a ring of separate steles surrounding a central one in aquatic Justicia). Primary medullary rays narrow.

The wood diffuse porous (mostly), or ring porous to semi-ring porous. The vessel end-walls simple. The vessels without vestured pits; without spiral thickening. The axial xylem without fibre tracheids; with libriform fibres; nearly always including septate fibres. The fibres without spiral thickening. The parenchyma usually sparse paratracheal. ‘Included’ phloem present (especially in Barlerieae), or absent. The wood not storied. Tyloses present, or absent.

Reproductive type, pollination. Plants hermaphrodite. Pollination entomophilous; mechanism conspicuously specialized (commonly exhibiting a loose-pollen mechanism, cf. Scophulariaceae etc. — e.g. the large bee-flowers of Acanthus), or unspecialized.

Inflorescence, floral, fruit and seed morphology. Flowers solitary, or aggregated in ‘inflorescences’; when aggregated, in cymes, or in racemes, or in verticils. The ultimate inflorescence units 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 irregularity 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; variously entire, or lobulate, or blunt-lobed. Calyx lobes markedly shorter than the tube to markedly longer than the tube. Degree of gamosepaly (maximum length joined/total calyx length) 0.5–0.9. Calyx imbricate, or valvate, or contorted, or open in bud; when K5, with the median member posterior. Corolla 4, or 5, or 3 (when the upper lip is suppressed); 1 whorled; gamopetalous (at least basally). Corolla tube not noticeably adaxially split, or adaxially deeply split (in Acanthus and relatives, where the upper lip of the corolla is cut away almost to the base of the tube). Corolla lobes markedly shorter than the tube to markedly longer than the tube. Degree of gamopetaly 0.5–0.75. Corolla imbricate (ascending cochlear or quincuncial), or contorted (left or right), or with open aestivation (only in Acanthus?); 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 (rarely, e.g. Pentstemonacanthus), or including staminodes. Staminodes when present, 1–3; in the same series as the fertile stamens; representing the posterior median member, or the posterior median member and the posterior-lateral pair, or the anterior-lateral pair. Fertile stamens representing the anterior-lateral pair, or the posterior-lateral pair and the anterior-lateral pair (commonly), or the posterior-lateral pair (Brillantaisia only). Stamens 4(–5), or 2; inserted near the base of the corolla tube, or midway down the corolla tube, or in the throat of the corolla tube; didynamous (in about 75% of the species), or not didynamous, not tetradynamous; reduced in number relative to the adjacent perianth (mostly), or isomerous with the perianth; oppositisepalous; 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. Endothecium developing fibrous thickenings (usually), or not developing fibrous thickenings (e.g. Barleria, Justicia, Ruellia). Anther epidermis persistent. Microsporogenesis simultaneous. Anther wall initially with one middle layer; of the ‘dicot’ type. Tapetum glandular. Pollen monosiphonous; shed as single grains. Pollen grains aperturate, or nonaperturate (rarely); 2–8 aperturate; colpate, or porate, or colporate, or foraminate; 2-celled (recorded in 11 genera), or 3-celled (in Barleria and Ruellia).

Gynoecium 2 carpelled. The pistil 2 celled. Gynoecium syncarpous; synstylovarious to eu-syncarpous; superior. Ovary 2 locular. Gynoecium median. Ovary sessile. Styles 1; attenuate from the ovary; apical; much longer than the ovary (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; unitegmic. Endothelium not differentiated. Embryo-sac development Polygonum-type. Polar nuclei fusing only after one has been fertilized. Antipodal cells formed; when not proliferated, 3; proliferating (occasionally, to 4–18 cells), or not proliferating; ephemeral (usually), or persistent. Synergids pear-shaped. Endosperm formation cellular. Endosperm haustoria present; chalazal and micropylar (‘terminal’, the latter usually the more aggressive). Embryogeny onagrad, or solanad.

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; large, planoconvex or crumpled. Embryo achlorophyllous (3/3); large. Testa sometimes covered with hairs or scales which become sticky or slimy when wet. Polyembryony recorded (and common).

Seedling. Germination phanerocotylar.

Physiology, phytochemistry. C3, or C4. C3 physiology recorded directly in Adhatoda, Barleria, Beleropone, Fittonia, Graptophyllum, Justicia, Lepidogathis. C4 physiology recorded directly in Blepharis. Anatomy non-C4 type (Acanthopale, Acanthus, Adhatoda, Asystasia, Barleria, Crabbea, Crossandra, Dyschoriste, Echolium, Eremomastax, Hypoestes, Isoglossa, Justicia, Lepidagathis, Monechma, Monothecium, Peristrophe, Phaulopsis, Rhinacanthus, Ruellia, Ruttya, Whitfieldia), or C4 type (Blepharis). Cyanogenic (rarely), or not cyanogenic. Alkaloids present, or absent. Anthraquinones detected (Barleria); derived from shikimic acid. Verbascosides detected (5 genera). Iridoids detected (in subfamilies Acanthoideae and Ruellioideae); ‘Route II’ type (normal and decarb.). Saponins/sapogenins present (rarely), or absent. Proanthocyanidins absent. Flavonols present (rarely), or absent; when present, kaempferol and quercetin (traces). Ellagic acid absent (8 species, 7 genera). Aluminium accumulation not found.

Special distinguishing feature. The seeds on elongated, indurated, hook-shaped funicles (‘retinacula’).

Geography, cytology. Holarctic, Paleotropical, Neotropical, Cape, and Australian. Temperate to tropical (mainly tropical). Centred on Indomalaysia, Africa, Brazil and central America. X = 7–21.

Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Lamiiflorae; Scrophulariales. Cronquist’s Subclass Asteridae; Scrophulariales. APG 3 core angiosperms; core eudicot; Superorder Asteranae; lamiid; Order Lamiales.

Species about 2400. Genera about 250; Acanthopale, Acanthopsis, Acanthostelma, Acanthura, Acanthus, Achyrocalyx, Adhatoda, Afrofittonia, Ambongia, Ancistranthus, Ancistrostylis, Andrographis, Angkalanthus, Anisacanthus, Anisosepalum, Anisostachya, Anisotes, Apassalus, Aphanosperma, Aphelandra, Aphelandrella, Ascotheca, Asystasia, Asystasiella, Ballochia, Barleria, Barleriola, Beloperone, Benoicanthus, Blechum, Blepharis, Borneacanthus, Boutonia, Brachystephanus, Bravaisia, Brillantaisia, Buceragenia, Calacanthus, Calophanoides, Calycacanthus, Camarotea, Carlowrightia, Celerina, Cephalacanthus, Chaetacanthus, Chalarothyrsus, Chameranthemum, Championella, Chileranthemum, Chlamydocardia, Chlamydostachya, Chroesthes, Clinacanthus, Clistax, Codonacanthus, Conocalyx, Corymbostachys, Cosmianthemum, Crabbea, Crossandra, Crossandrella, Cyclacanthus, Cylindrosolenium, Cyphacanthus, Dactylostegium, Danguya, Dasytropis, Dichazothece, Dicladanthera, Dicliptera, Didyplosandra, Dipteracanthus, Dischistocalyx, Dolichostachys, Drejera, Drejerella, Duosperma, Dyschoriste, Ecbolium, Echinacanthus, Encephalosphaera, Epiclastopelma, Eranthemum, Eremomastax, Eusiphon, Filetia, Fittonia, Forcipella, Forsythiopsis, Gastranthus, Geissomeria, Glossocheilus, Golaea, Graphandra, Graptophyllum, Gymnophragma, Gymnostachyum, Gynocraterium, Gypsacanthus, Habracanthus, Hansteinia, Haplanthodes, Harpochilus, Henrya, Herpetacanthus, Heteradelphia, Holographis, Hoverdenia, Hulemacanthus, Hygrophila, Hypoestes, Ichthyostoma, Indoneesiella, Ionacanthus, Isoglossa, Isotheca, Jadunia, Juruasia, Justicia, Kalbreyeracanthus, Kalbreyeriella, Kosmosiphon, Kudoacanthus, Lankesteria, Lasiocladus, Leandriella, Lepidagathis, Leptostachya, Liberatia, Linariantha, Lindauea, Lophostachys, Louteridium, Lychniothyrsus, Mackaya, Marcania, Megalochlamys, Megalostoma, Megaskepasma, Melittacanthus, Mellera, Metarungia, Mexacanthus, Mimulopsis, Mirandea, Monothecium, Morsacanthus, Neohallia, Neriacanthus, Neuracanthus, Odontonema, Odontonemella, Ophiorrhiziphyllon, Oplonia, Oreacanthus, Orophochilus, Pachystachys, Pelecostemon, Pentstemonacanthus, Perenideboles, Pericalypta, Periestes, Peristrophe, Petalidium, Phaulopsis, Phialacanthus, Phidiasia, Phlogacanthus, Physacanthus, Podorungia, Poikilacanthus, Polylychnis, Pranceacanthus, Pseuderanthemum, Pseudodicliptera, Pseudoruellia, Psilanthele, Ptyssiglottis, Pulchranthus, Pupilla, Razisea, Rhinacanthus, Rhombochlamys, Ritonia, Rostellularia, Ruellia, Ruelliopsis, Rungia, Ruspolia, Ruttya, Salpinctium, Salpixantha, Samuelssonia, Sanchezia, Santapaua, Sapphoa, Satanocrater, Sautiera, Schaueria, Schwabea, Sciaphyllum, Sclerochiton, Sebastiano-schaueria, Siphonoglossa, Spathacanthus, Sphacanthus, Sphinctacanthus, Spirostigma, Standleyacanthus, Steirosanchezia, Stenandriopsis, Stenandrium, Stenostephanus, Stephanophysum, Streblacanthus, Streptosiphon, Strobilanthes, Strobilanthopsis, Styasasia, Suessenguthia, Synchoriste, Taeniandra, Tarphochlamys, Teliostachya, Tessmanniacanthus, Tetramerium, Theileamea, Thomandersia (Thomandersiaceae), Thyanostigma, Tremacanthus, Triaenanthus, Trichanthera, Trichocalyx, Ulleria, Vavara, Vindasia, Warpuria, Xantheranthemum, Xerothamnella, Yeatesia, Zygoruellia.

General remarks. For summarised differences between this attempted compilation of data for Acanthaceae sensu stricto and seemingly closely related segregate families, see the descriptions of Nelsoniaceae, Mendonciaceae and Thunbergiaceae.

Economic uses, etc. A few cultivated ornamentals: Acanthus, Aphelandra, Fittonia, Beloperone, Justicia, etc.

Illustrations. • Technical details - Adhatoda (~Justicia), Ruellia. • Technical details - Justicia (Thonner). • Acanthus (inflorescence). • Aphelandra acanthifolia: Hook. Ic. Pl. 2 (1837). • Brachystephanus giganteus, as Oreacanthus mannii: Hook. Ic. Pl. 13 (1877–79). • Barleria hochstetteri: Hook. Ic. Pl. 9 (1852). • cf. Barleria argentea, as Somalia diffusa: Hook. Ic. Pl. 16 (1886). • Beloperone oblongata: Bot. Reg. 1657, 1835. • Justicia peruviana: Bot. Mag. 430, 1799. • Justicia patentiflora: Hook. Ic. Pl. 28 (1905). • Justicia quadrangularis: Bot. Reg. 1340, 1830. • Justicia venusta: Bot. Reg. 1380, 1830. • Pachystachys coccinea: Bot. Mag. 432, 1799. • Satanocrater paradoxa: Hook. Ic. Pl. 30 (1913). • Strobilanthes sabinianus: Bot. Reg. 1238, 1829. • Strobilanthes scaber: as S. scabra, Bot. Reg. 32, 1841. • Thomandersia laurentii, as Scytanthus laurifolius: Hook. Ic. Pl. 13 (1877–79). • Foliar cystoliths in Asystasia, Barleria, Justicia, Sanchezia and Stephanophysum (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: 20th June 2017.’.