Key for Acanthaceae

1Herbs, subshrubs, vines or climbers; seeds not borne on prominent, hook-shaped retinaculum (funicle), retinaculum papilliform or lacking
1'Herbs, shrubs or small trees (not vines or climbers); seeds borne on prominent, hook-shaped retinaculum (funicle)
2Vines, climbers or shrubs; capsule with a prominent sterile apical beak much narrower and longer than the fertile globose base; calyx unlobed (annular) or unequally 10-17-lobed; ovules 4
2'Herbs; capsule lacking a prominent sterile beak (a beak, if present, not conspicuous, similar in width to seed-bearing portion of capsule); calyx 2-5-lobed; ovules 6-24
3Bracteoles 2; calyx deeply 5-lobed, lobes ± equal; corolla tubular, limb subbilabiate; stamens 4; capsule oblong, obtuse, seed-bearing nearly its entire length; seeds numerous: 25-30 (only 6 in Gynocraterium), without numerous cristae
3'Bracteoles absent; calyx 4-lobed, lower lobe apically 2-dentate; corolla not tubular, limb bilabiate; stamens 2; capsule conical, beaked, seed-bearing only at base; seeds 8-28, with numerous cristae
4Ovules 6; stigma crateriform
4'Ovules numerous 25-30; stigma 2- or 3-parted
5Fertile stamens usually 4
5'Fertile stamens 2
6Anthers 1-thecous; cystoliths absent; corolla imbricate in bud
6'Anthers 2-thecous or anthers of the longer pair 2-thecous, those of the shorter pair 1-thecous (Herpetacanthus); cystoliths present; corolla contorted in bud
7Corolla limb bilabiate, 2-lobed
7'Corolla limb deeply divided to throat, forming a 5-lobed lip; plants cultivated
8Inflorescence of densely bracted, elongate, 4-sided dichasiate spikes; bracts imbricate, ovate-lanceolate to ovate to oblong to suborbicular, green or green and turning indigo upon drying
8'Inflorescence and bracts otherwise
9Plants sprawling or erect perennial herbs 30-70 cm tall; leaf blades narrowly ovate to elliptic, green on both surfaces; bracts species is cultivated in gardens in French Guiana and occasionally escapes broadly ovate to cordate, 5.5-14 mm wide; corolla pale lavender to purple to whitish
9'Plants low-growing, diffuse herbs 30-35 cm tall; leaf blades broadly ovate to ovate-oblong to cordate, lower surface purple, portions turning indigo upon drying; bracts ovate-lanceolate to oblong, 4.5 mm wide; corolla white; plants native to Malaysia, in French Guiana cultivated in gardens, occasionally escapes
10Anthers of the longer pair of stamens 2-thecous, thecae superposed or somewhat obliquely attached to connective, those of the shorter pair of stamens 1-thecous
10'Anthers of both pairs of didynamous stamens 2-thecous, thecae ± equally attached to connective
11Calyx lobes heteromorphic (anterior and posterior) lobes longer than inner (lateral) ones
11'Calyx lobes homomorphic or nearly regular (or if heteromorphic then not with lobes as described above)
12Calyx 4-lobed; corolla large and conspicuous, 35-45 mm long; erect herbs or shrubs, often spiny in branch axils
12'Calyx 5-lobed; corolla small, 2-lipped, 4.5-6.5 mm long; diffuse or rarely erect herbs, not spiny
13Large shrubs or trees; calyx lobes often rounded or obtuse apically
13'Herbs, often ± suffrutescent (rarely shrubs); calyx lobes subulate or lanceolate, acute or acuminate apically
14Corolla limb zygomorphic (2 lobes of upper lip considerably smaller than lobes of lower lip); flowers solitary or fascicled axillary; mature calyx tube often rupturing in weak hyaline regions between lobes; capsule cylindric, estipitate
14'Corolla limb subactinomorphic (or at least the 5 lobes subequal in size; flowers variously arranged but not appearing as verticels; mature calyx tube not splitting between lobes; capsule stipitate
15Inflorescence of secund racemes; corolla yellowish with purplish throat when dry
15'Inflorescence an axillary, branching, long peduncled dichasium or cyme or, 1-2(-3) more or less sessile, occasionally long pedicellate flowers in upper axils, combined into a terminal raceme or spike; corolla variously colored, but not yellowish with purple throat when dry
16Inflorescence narrow, terminal and axillary panicles; corolla tubular, not ventricose or distinctly curved, bright red or yellowish, limb short, bilabiate, not at all spreading, upper 2 lobes united into a bilobed upper lip; disk annular with distinct projections
16'Inflorescence branching axillary, once or twice dichasially branched, long-pedunculate dichasia or cyme; corolla infundibuliform or salverform, occasionally saccate, limb of 5 equal, spreading lobes, these nearly regular, purple, lavender, whitish, occasionally red or rose colored (then tube curved and ventricose); disk annular, without distinct projections
17Androecium of 2 fertile stamens and 2 staminodes; flowers sometimes heterostylous
17'Androecium of 2 fertile stamens and 0 staminodes; flowers never heterostylous
18Flowers heterostylous; corolla limb equally or subequally 5-lobed; bracts imbricate, conspicuously variegated white and green
18'Flowers rarely heterostylous; corolla limb 2-lipped (weakly so in Odontonema); bracts not imbricate, inconspicuous, small, green
19Corolla red to reddish-purple or sometimes white, weakly bilabiate, lobes not dotted, tube long, slender, straight; anthers included within corolla or exserted due to heterostyly; rachis and calyx glabrous or pubescent, rarely glandular-puberulent
19'Corolla lilac with darker spots on limb, strongly bilabiate, tube short, broad and curved; anthers exserted; rachis and calyx glandular-puberulent
20Anther 2-thecous, thecae parallel to subsagittate, nearly equal in length
20'Anthers variously 1- or 2-thecous, thecae superposed, usually ± dissimilar in length
21Inflorescence spicate; bracts conspicuous and/or imbricate, 4-17 mm wide
21'Inflorescence panicled racemes; bracts inconspicuous, triangular, 0.5 mm wide
22Stem and rachis brown-puberulous; bracts ovate, 30-44 x 11-17 mm, dark pink, purple or red; corolla white distally, grading to dark pink proximally; plants cultivated
22'Stem and rachis glabrous or nearly so; bracts ovate to lanceolate, 15-25 x 4-11 mm, green; corolla bright red, scarlet or becoming orange-red with age
23Stems hexagonal; inflorescence of axillary bracteate cymes bearing 1 or more sessile to pedunculate cymules, cymules consisting of 1 or more flowers subtended by an involucre of 2 or 4 bracteoles, outer pair of cymule bracteoles conspicuous and larger than inner pair(s); retinacula separating from inner capsule wall at maturity and protruding prominently from each valve of capsule, mature capsule conspicuously ruptured near base of head; corolla resupinate
23'Stems terete to quadrate; inflorescence various but not as described above, cymules never present, flowers subtended by 1 pair of bracteoles; retinacula remaining attached to inner capsule wall at maturity, protruding prominently from each valve of capsule, mature capsule not ruptured near base of head; corolla never resupinate