Sp. Pl. 2: 693. 1753.
Gen. Pl. ed. 5, 310. 1754.
Herbs, annual or perennial, subshrubs, shrubs, or trees, glabrous or hairy. Stems erect, Inflorescences axillary, sometimes adnate to subtending petiole (H. moscheutos), flowers solitary or clustered; involucel present, bractlets usually persistent, rarely deciduous (H. mutabilis), 6–16, rarely minute or absent (H. denudatus), distinct, undivided, 2-fid or appendaged (H. acetosella, H. aculeatus, H. furcellatus, H. radiatus). Flowers usually lasting for a day; calyx persistent, sometimes accrescent, inflated or not, not spathaceous, primary-veins usually ± straight, rarely zigzag (H. trionum, sometimes H. dasycalyx), lobes triangular to trullate, sometimes strongly 3-ribbed (H. acetosella, H. aculeatus, H. furcellatus, H. radiatus), sometimes with nectary on midrib; corolla radial or weakly bilaterally symmetric, narrowly funnelform to broadly campanulate or rotate or petals sometimes recurved (H. clypeatus), white, cream, yellow, orange, pink, red, lavender, purple, or blue, usually red, purple, or brown basally; staminal column included or exserted (H. coccineus, H. poeppigii, H. schizopetalus); ovary 5-carpellate; ovules 8–60 per carpel; styles 5-branched from or beyond orifice of staminal column; stigmas capitate to discoid or wedge-shaped (H. striatus). Fruits capsules, 5-valved, ovoid or spheroid, apex usually apiculate, acute, or acuminate, sometimes rounded or depressed or impressed, glabrous or hairy. Seeds to 60 per locule, reniform-ovoid, reniform-globose, or subglobose, sometimes angulate, sometimes laterally compressed or impressed, papillose or not, glabrous or hairy. x = 10, 11, [12,] 14, [15–17,] 18, 19, [20,] 26, [27,] and probably higher.
North America, Mexico, West Indies, Central America, South America, Eurasia, Africa, Indian Ocean Islands, Pacific Ocean Islands, Australia
Species ca. 350 (21 in the flora).
Taxonomy of Hibiscus is in flux. Molecular studies place members of some other genera in Hibiscus as traditionally circumscribed, indicating paraphyly (B. E. Pfeil and M. D. Crisp 2005). Neither of the two solutions to this problem—vastly expanding the circumscription of Hibiscus to include the nested genera, or breaking Hibiscus into smaller genera—has been attempted here.
The 21 species of Hibiscus in the flora area are scattered among nine sections. The sections follows: sect. Hibiscus (species 1), sect. Bombicella de Candolle (species 2–6), sect. Furcaria de Candolle (species 7–10), sect. Lilibiscus Hochreutiner (species 11 and 12), sect. Muenchhusia (Heister ex Fabricius) O. J. Blanchard (species 13–17), sect. Venusti Ulbrich (species 18), sect. Striati O. J. Blanchard (species 19), sect. Trionum de Candolle (species 20), and sect. Clypeati O. J. Blanchard (species 21).
Most Hibiscus species in the flora area are native; seven were introduced into North America either for horticultural purposes (H. acetosella, H. mutabilis, H. rosa-sinensis, H. schizopetalus, H. syriacus, and H. trionum) or as fiber crops (H. radiatus). Experimental crosses among some native species (H. coccineus, H. grandiflorus, H. laevis, and H. moscheutos) have been the basis of selections of hardy Hibiscus available in the horticultural trade. A popular cultivated form in the South is the result of an experimental cross involving a complex interspecific hybrid combining H. coccineus, H. laevis, and H. moscheutos as the staminate parent and H. mutabilis as the pistillate parent (H. F. Winters 1970).
North American taxa in the speciose sect. Bombicella share a base chromosome number of × = 11 (chromosome numbers are unknown for Hibiscus coulteri); those in sect. Furcaria, × = 18; and those in sect. Muenchhusia, × = 19. Base numbers of the two sections represented in the flora area by one native species each are 10 and 26, and cannot be readily reconciled between themselves or with the others. The remaining four sections together include five species, all of which are non-natives and, except for H. trionum, have long histories in cultivation and multiple different chromosome numbers that are not easily evaluated. This overall chromosomal diversity supports the molecular evidence for a polyphyletic Hibiscus.
Extensive experimental hybridization work in sect. Furcaria, and the study of chromosome pairing relationships in these hybrids, indicate that the native species Hibiscus aculeatus and H. furcellatus, both tetraploids, share the genomic makeup GGPP, while the introduced species H. acetosella and H. radiatus, also tetraploids, share AABB (F. D. Wilson 1994).
A naturally occurring hybrid between Hibiscus coulteri and H. denudatus (Hibiscus ×sabei Weckesser) has been documented from western Texas (W. Weckesser 2011).
Some desert species of Hibiscus sometimes produce cleistogamous flowers. Foliar nectaries are present abaxially near the base of the midvein in some species.
Three species of Hibiscus are of doubtful status in the flora area. Hibiscus cannabinus Linnaeus and H. sabdariffa Linnaeus have both been cultivated in the southern states as fiber crops, and the latter also for its fleshy calyces, which are used to flavor beverages. It is doubtful that either has become established in the flora area. Hibiscus bifurcatus Cavanilles is widely distributed from the West Indies and Guatemala to South America; it was documented with two collections from Dade County in Florida by R. Woodbury in 1949 and 1950, but since Woodbury was involved at the time in establishing what later became the John C. Gifford Arboretum in Coral Gables south of Miami, there is a good chance that the source was a plant in cultivation.
|1||Leaf blades glabrous or glabrate abaxially, sometimes with few hairs or prickles on veins||> 2|
|1||Leaf blades variously hairy abaxially: stellate-hairy, scabrous, scabridulous, tomentose, stellate-tomentose, tomentulose, or velvety||> 12|
|2||Calyx lobes conspicuously 3-ribbed, 2 marginal, 1 medial||> 3|
|2||Calyx lobes not conspicuously 3-ribbed||> 4|
|3||Calyx lobes with nectary on medial rib; herbage usually dark red.||Hibiscus acetosella|
|3||Calyx lobes without nectary; herbage not dark red.||Hibiscus radiatus|
|4||Plants annual, to 0.6(–1) m; petals mostly 1.5–3(–4) cm; calyx: primary veins zigzag; leaf blades 3(–5)-parted, segments pinnately lobed, lobes apically rounded or truncate.||Hibiscus trionum|
|4||Plants perennial, usually 1–5 m; petals 3.5–10.5 cm; calyx: primary veins not zigzag (except sometimes in H. dasycalyx, then petals 4–7 cm); leaf blades unlobed or, if parted, with segments not both pinnately lobed and lobes apically rounded or truncate||> 5|
|5||Leaf blades usually unlobed (rarely lobed in H. rosa-sinensis)||> 6|
|5||Leaf blades 3-lobed, sometimes hastately, or palmately 3–5-lobed||> 9|
|6||Petals pinnatifid-laciniate, strongly reflexed; involucellar bractlets 0.06–0.18 cm.||Hibiscus schizopetalus|
|6||Petals not pinnatifid-laciniate, spreading or slightly reflexed; involucellar bractlets 0.3–3 cm||> 7|
|7||Calyces conspicuously enlarging in fruit; widespread native herbaceous perennials of open wetlands.||Hibiscus laevis|
|7||Calyces not or little enlarging in fruit; woody plants of cultivation, occasionally escaping and then into nonwetland habitats||> 8|
|8||Staminal column bearing filaments nearly throughout; capsules minutely densely stellate-hairy; temperate North America.||Hibiscus syriacus|
|8||Staminal column bearing filaments in distal 1/2; capsules seldom produced, glabrous; s California, s Florida.||Hibiscus rosa-sinensis|
|9||Leaf blades 3–5-lobed; petals bright red.||Hibiscus coccineus|
|9||Leaf blades 3-lobed; petals pink, lavender, blue, white, creamy white, or cream, reddish basally||> 10|
|10||Calyces divided 1/2 length, little enlarging in fruit; seeds flattened, reniform-ovoid, glabrous laterally, hairy dorsally; cultivated shrubs escaping into nonwetland habitats.||Hibiscus syriacus|
|10||Calyces divided 1/3–1/2 length, conspicuously enlarging in fruit; seeds reniform-globose, hairy throughout; native herbs of open wetlands||> 11|
|11||Calyces and capsules glabrous; e, c United States.||Hibiscus laevis|
|11||Calyces and capsules hairy; Texas.||Hibiscus dasycalyx|
|12||Involucellar bractlets: apex 2-fid or appendaged; calyx lobes with nectaries on medial ribs; petals maroon, red, or purple-brown basally||> 13|
|12||Involucellar bractlets (often absent in H. denudatus): apex not 2-fid or appendaged; calyx lobes without nectaries; petals with or without maroon, red, or purple-brown basally||> 14|
|13||Stems and leaf blades scabrous; petals pale yellow to white.||Hibiscus aculeatus|
|13||Stems and leaf blades stellate-tomentulose; petals pink.||Hibiscus furcellatus|
|14||Plants annual; calyces: primary veins zigzag; leaf blades 3(–5)-parted, segments pinnately lobed, lobes apically rounded or truncate.||Hibiscus trionum|
|14||Plants perennial: subshrubs, shrubs, trees, or herbaceous perennials; calyces: primary veins not zigzag; leaf blades unlobed or, if parted, with segments not both pinnately lobed and lobes apically rounded or truncate||> 15|
|15||Petals abaxially tomentose, somewhat revolute, dull red or dull orange; seeds glabrous; s Texas.||Hibiscus clypeatus|
|15||Petals not abaxially tomentose (sometimes sparsely hairy abaxially where exposed in bud), bright red, yellow, cream, pink, maroon, mauve, pale purple, or white, often with pink, red, or maroon lines or spot basally; seeds verrucose-papillose or hairy; s Florida and sw United States including Texas||> 16|
|16||Petals bright red throughout||> 17|
|16||Petals yellow, cream, pink, mauve, pale purple, or white, usually with contrasting spots or lines near base||> 18|
|17||Flowers horizontal or ascending, corolla broadly campanulate to rotate; involucellar bractlets 1.2–2(–2.4) cm; s Texas.||Hibiscus martianus|
|17||Flowers nodding or pendulous, corolla narrowly funnelform; involucellar bractlets 0.5–0.9 cm; s Florida.||Hibiscus poeppigii|
|18||Pedicels nearly always much longer than subtending leaves||> 19|
|18||Pedicels shorter than subtending leaves (or else subtending leaves much reduced or absent in subcorymbose inflorescences of some H. mutabilis)||> 20|
|19||Stellate hairs of young stems dense, appressed, 4-armed, aligned with stem axis; seeds silky-hairy ± throughout.||Hibiscus coulteri|
|19||Stellate hairs of young stems sparse, few- to many-armed, 2- or 3-dimensionally radiate; seeds glabrous laterally.||Hibiscus biseptus|
|20||Leaves mostly 1.2–3 cm; petals 1.3–3 cm; desert Southwest.||Hibiscus denudatus|
|20||Leaves mostly 4–30 cm; collectively widespread but almost never in desert Southwest||> 21|
|21||Stems at least remotely prickly; free portion of stamen filaments 1–1.5 mm; stigmas wedge-shaped; seeds tomentulose||Hibiscus striatus|
|21||Stems unarmed; free portion of stamen filaments 2–9 mm; stigmas capitate or discoid; seeds verrucose-papillose or with long straight hairs dorsally and dorsolaterally||> 22|
|22||Subshrubs, shrubs, or trees; capsules: apex impressed; seeds with long straight hairs dorsally and dorsolaterally; plants of cultivation, escaping rarely (Alabama, Louisiana), and then into nonwetland habitats||Hibiscus mutabilis|
|22||Perennial herbs; capsules: apex apiculate; seeds verrucose-papillose; widespread (Ontario, e, sc United States and California) species of open wetlands||> 23|
|23||Staminal columns: length 1/2 petals; filaments: free portions not secund; pedicels of later-produced flowers often adnate to petioles.||Hibiscus moscheutos|
|23||Staminal columns: length 2/3 petals; filaments: free portions secund; pedicels never adnate to petioles.||Hibiscus grandiflorus|