Acantheae

Manzitto-Tripp, Erin A., Darbyshire, Iain, Daniel, Lucinda A. McDade Thomas F. & Kiel, Carrie A., 2022, Revised classification of Acanthaceae and worldwide dichotomous keys, TAXON 71 (1), pp. 103-153 : 122

Key to the genera of Acantheae

1 Corolla regularly 5-lobed or bilabiate, not comprising a single lip.... 2

1 Corolla lobes comprising a single lip, entire or 3- or 5-lobed, held either ventrally or dorsally, or if (rarely) not markedly 1-lipped [3] then at least with the sinus between the 2 uppermost (outermost) lobes clearly at a wider angle than that of the other sinuses ........ 8

2 Plants of tropical Africa and Madagascar........ Stenandriopsis [4]

2 Plants of the Americas................................................................. 3

3 Corolla zygomorphic, the lobes dissimilar in form ..................... 4

3 Corolla usually subactinomorphic, the lobes more or less similar in form (or nearly zygomorphic with lobes of upper lip dissimilar from those of lower lip in some Stenandrium ) ............................ 6

4 Calyx deeply 3-partite............................................. Cyphacanthus

4 Calyx 5-partite ............................................................................. 5

5 Leaves opposite (rarely subopposite), not quaternate; bracts entire or dentate, green or often brightly colored; corollas rarely with linear nectar guides, mostly 25–85 mm long; at least distal portion of filaments of stamens usually exserted from corolla tube; pollen with colpi not expanded or bifurcating (usually narrowed) toward poles, interapertural exine usually heterogeneously sculptured; plants typically of wet habitats; widespread in NW.................. Aphelandra [5]

5 Leaves opposite (rarely subopposite) or quaternate; bracts entire and usually green; corolla often with colored linear nectar guides, 6.5–24 mm long (or if longer [to 40 mm], then plants with quaternate leaves); filaments of stamens often entirely included in corolla tube; pollen with colpi sometimes expanded or bifurcating toward poles, interapertural exine homogeneously sculptured; plants of dry habitats; Mexico.................................................. Holographis

6 Pollen 3-colpate with each colpus longitudinally bisected by an operculum (elongate band of exine), opercula either isolated within the colpi (operculate) or connected at each end to the interapertural exine (pontoperculate); Jamaica................................ Salpixantha [6]

6 Pollen 3-colpate with colpi not bisected by elongate bands of exine or pollen pantoforate (i.e., sometimes in Stenandrium dulce ) or pollen pantoaperturate (rugate) with rugae arranged ± tangentially or irregularly over surface or pollen 3-colpate and with prominent margines and mesocolpial ridges (appearing 9-colpate); widespread, but not in Jamaica............................................................ 7

7 Plants usually small, up to 25(–70) cm; leaves often borne at or near ground level (plants acaulescent to subcaulescent); bracts usually green; widespread .............................................. Stenandrium

7 Plants usually shrubby, up to 1.5 m tall; leaves disposed along conspicuous stems; bracts whitish, pinkish, or reddish-brown; Central America and South America............................... Neriacanthus [6]

8 Corolla tube twisted through 180°, the single corolla lip held dorsally, entire or 3-lobed; Tanzania............................. Streptosiphon

8 Corolla tube not twisted, corolla lip held ventrally, 3- or 5-lobed or sometimes only undulate ............................................................. 9

9 Stamens included in corolla tube, anthers subsessile, not inserted on a thickened flange................................................................. 10

9 Stamens exserted from corolla tube, with flattened bone-like filaments, inserted on a thickened flange........................................ 11

10 Calyx 4-lobed, anterior lobe bifid; bracts not imbricate, smaller than bracteoles; bracteoles conspicuous, elliptic or obovate, diverging widely from inflorescence axis; corolla tube not narrowly cylindrical, limb obscurely 5-lobed or erose .......................... Crossandrella

10 Calyx 5-lobed; bracts usually imbricate, larger than and enclosing bracteoles; bracteoles linear to lanceolate, not diverging widely from inflorescence axis; corolla tube narrowly cylindrical, limb 5-lobed........................................................................ Crossandra

11 Calyx 5-lobed; seeds sculpted with pectinate scales or concentric rings; bracts, bracteoles and calyx lobes glumaceous ... Sclerochiton

11 Calyx 4-lobed; seeds either covered in hygroscopic trichomes, puberulous or glabrous, or seeds tuberculate, without scales or concentric rings; bracts, bracteoles and calyces only rarely glumaceous......................................................................... 12

12 Anterior pair of staminal filaments flattened and either with an obtuse or acute tooth-like appendage or truncate to rounded towards apex ventrally ............................................................................ 13

12 Anterior staminal filaments lacking appendages, if flattened then gradually narrowed towards apex .............................................. 14

13 Leaves opposite; flowers solitary or paired in leaf axils, each subtended by 2 pairs of bracteoles, outer pair entire, inner pair trifid; ovary without apical tufts of glandular trichomes; seeds tuberculate; India............................................................ Cynarospermum

13 Leaves in pseudowhorls of (3) 4; inflorescences variable but not with single or paired flowers in leaf axils; bracteoles entire or toothed, not trifid; ovary with 2 apical tufts of glandular trichomes; seeds with branched hygroscopic trichomes; widespread.............. ....................................................................................... Blepharis

14 Seeds glabrous or sericeous-puberulous; stigma bilobed; bracts terminating in a single spine; plants often robust, ± tall perennial herbs, shrubs or small trees; widespread ........................ Acanthus

14 Seeds covered in long hygroscopic trichomes; stigma 1-lobed; bracts terminating in 3 or 5 simple or compound spines; plants often compact shrublets or acaulescent perennial herbs, if taller then slender; SW Africa .................................................... Acanthopsis