Rose-mallow [Greek hibiscus or ibiscum, alluding to cohabitation with Ibis, stork, in marshes] Rose-mallow [Greek hibiscus or ibiscum, alluding to cohabitation with Ibis, stork, in marshes]

Orland J. Blanchard Jr.

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.

Species ca. 350 (21 in the flora): North America, Mexico, West Indies, Central America, South America, Eurasia, Africa, Indian Ocean Islands, Pacific Ocean Islands, Australia.

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.

SELECTED REFERENCES Bates, D. M. 1965. Notes on the cultivated Malvaceae, 1. Hibiscus. Baileya 13: 56–130. Blanchard, O. J. 1976. A Revision of Species Segregated from Hibiscus Sect. Trionum (Medicus) de Candolle Sensu Lato (Malvaceae). Ph.D. dissertation. Cornell University. Fryxell, P. A. 1980. A Revision of the American Species of Hibiscus Section Bombicella (Malvaceae). Washington. [U.S.D.A. Techn. Bull. 1624.] Hochreutiner, B. P. G. 1900. Révision du genre Hibiscus. Annuaire Conserv. Jard. Bot. Genève 4: 23–190. Kearney, T. H. 1955b. A tentative key to the North American species of Hibiscus L. Leafl. W. Bot. 7: 274–284. Menzel, M. Y., P. A. Fryxell, and F. D. Wilson. 1983. Relationships among New World species of Hibiscus section Furcaria (Malvaceae). Brittonia 35: 204–221.