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Section Furcaria is the most diverse section of Hibiscus, containing over 100 species. It contains a number of species of economic importance, such as kenaf (Hibiscus cannabinus), roselle (Hibiscus sabdariffa) and false roselle (Hibiscus acetosella). Several species are also grown as ornamentals, though they don't have the popularity of Hibiscus rosa-sinensis, Hibiscus syriacus or Hibiscus moscheutos. As a result of these uses the group is relatively well studied.
The section was originally conceived as being composed of those species of Hibiscus whose bracteoles are either forked, or possess distinct terminal appendages. The current circumscription is wider. The key character is a calyx with each calyx lobe possessing a thickened midrib, and two thickened marginal ribs. [1]
F.D. Wilson surveyed the section in 2006 [1], identifying 103 species, and 6 subspecies and varieties, building on earlier reviews by himself and others of the section in Australia [2], Africa and Asia [3], Polynesia [4], and South America [5]. The 2006 review does not mention 4 species (Hibiscus bricchettii, Hibiscus keilii, Hibiscus paolii and Hibiscus saxicola) mentioned, but not explicitly rejected or accepted in the earlier African review, and also fails to mention an additional species, Hibiscus ceratophorus, described in the intervening period.
Some additional species have been described since 2006 [6, 7, 8].
Section Furcaria has a base (haploid) chromosome number of 18. There are 11 known diploid species, 1 native to the Americas, and the remainder native to Africa. The remaining species range from tetraploids to decaploids, and experimentally produced hybrids also include triploids, pentaploids, heptaploids and dodecaploids. On the basis of chromosome pairing in hybrids thirteen diploid genomes, have been identified, but more may exist among species that have not been investigated in this fashion. The A, B, G, X and Y genomes are found in diploids. With the exception of the X genome these are also known from polyploid species. Another 8 genomes, the C, D, E, H, J, P, R and V genomes, are only known from polyploid species. Ploidy level and genome composition, where known, are given below in the summary of the species. [9, 10, 11, 12, 13, 14, 15]
Hibiscus diversifolius (8x; CDEG) is pantropical, being found in Africa, Madagascar, Australia, the Pacific, and central and southern America. Two subspecies are recognised. Subsp. rivularis is found in Africa and eastern Brasil, and subsp. diversifolius throughout the range of the species.
Several species are shared between North and South America. In addition to Hibiscus diversifolius, Hibiscus furcellatus (4x: GP) is found from southern Florida, the Caribbean, and southern Mexico to Argentina and Bolivia, and also in Hawaii. Hibiscus bifurcatus (4x; PQ) extends from the Florida Keys, the Caribbean and Central America to Columbia, Venezuela, Surinam and northern Brasil (Para, Amazonas). [16] Hibiscus maculatus (10x; CDEGR), is native to Cuba, and to Colombia in South America.
North America has 3 endemic species. These are Hibiscus aculeatus (4x; GP) (southeastern USA), Hibiscus costatus (2x) (southern Mexico, Central America and Cuba) and Hibiscus uncinellus (4x; GP) (southern Mexico).
South America has 42 species, 5 of which are introduced (Hibiscus acetosella, Hibiscus cannabinus, Hibiscus mechowii, Hibiscus radiatus, Hibiscus sabdariffa). Endemic species are Hibiscus adscensionis (4x) (Bolivia), Hibiscus amambayensis (southern Brasil and northern Paraguay), Hibiscus andersonii (Mato Grosso), Hibiscus benensis (Bolivia), Hibiscus cabralensis (Minas Gerais), Hibiscus capitalensis (4x; GP) (Brasilian Distrito Federale), Hibiscus chancoae (Peru), Hibiscus chapadensis (Goias), Hibiscus conmixtus (Bolivia), Hibiscus conceptionis (Bolivia), Hibiscus cucuberitaceus (4x; GP) (Bahia, Minas Gerais and Paraguay) [16], Hibiscus ferreirae (eastern Bolivia and western Brasil), Hibiscus flagelliformis (4x) (Goias, Minas Gerais) [16], Hibiscus gregoryi (Goias), Hibiscus hasslerianus (Paraguay) [16], Hibiscus henningsianus (Matto Grosso) [16], Hibiscus hilairianus (Minas Gerais), Hibiscus hochreutineri (Mato Grosso, Tocantins), Hibiscus itirapinensis (Sao Paulo), Hibiscus kitaibelifolius (4x) (Minas Gerais, Sao Paulo) [16], Hibiscus laxiflorus (4x) (Goias, Distrito Federale, Minas Gerais, Matto Grosso) [16], Hibiscus mariae (Minas Gerais), Hibiscus matogrossensis (Mato Grosso, Goias), Hibiscus multiformis (4x; GP) (Minas Gerais), Hibiscus nanuzae (Minas Gerais), Hibiscus paludicola (north east Bolivia, north west Brasil), Hibiscus peruvianus (4x; GP) (western Amazon basin of Peru, Venezuela and Brasil) [16], Hibiscus pohlii (4x) (Brasilian Distrito Federale, Goias), Hibiscus saddii (Mato Grosso), Hibiscus sebastianii (Roraima) [17], Hibiscus trilineatus (Tocantins), Hibiscus urticifolius (Rio Grande do Sul) [16], Hibiscus wilsonii (4x) (central Brasil) [16] and Hibiscus windischii (Mato Grosso)
Africa (excluding Madagascar) has 32 species. Endemic species are Hibiscus acetosella (4x; AB) (widely naturalised outside Africa), Hibiscus altissimus (8x; BGS--) (southeastern Africa), Hibiscus asper (2x; A), H. berberidifolius (2x), Hibiscus cannabinus (2x; A), Hibiscus ceratophorus (Somalia), Hibiscus cuanzensis (Angola), Hibiscus elongatifolius (Cameroon), Hibiscus fabiana (West Africa) [7], Hibiscus flavo-roseus (Angola), Hibiscus furcellatoides (Guinea), Hibiscus gilletii (2x; X) (central Africa) (including subsp. hiernianus and subsp. lundaensis), Hibiscus goossensii (Congo), Hibiscus greenwayi (2x; A) (East Africa), Hibiscus mastersianus (2x; XMAS) (South and South West Africa, introduced into India), Hibiscus mechowii (2x; YMEC), Hibiscus moxicoensis (Angola), Hibiscus nigricaulis (2x) (southern Africa) (including Hibiscus meeusii), Hibiscus noldeae (4x) (west to east central Africa), Hibiscus parvilobus (Kenya), Hibiscus reekmansii (East Africa), Hibiscus rostellatus (4x; GH) (west to east central Africa), Hibiscus sabdariffa (4x; AY) (Angola to Ghana), Hibiscus scotellii (West Africa), Hibiscus sineaculeatus (Nigeria), Hibiscus sparseaculeatus (East Africa), Hibiscus sudanensis (2x; G) and Hibiscus torrei (southern East Africa). The remaining species are Hibiscus diversifolius and Hibiscus surattensis.
Madagascar has two endemic species, Hibiscus partitus and Hibiscus subdiversifolius. Hibiscus cannabinus, Hibiscus diversifolius and Hibiscus surratensis are also found in Madagascar.
Hibiscus surattensis (2x; B) is shared between Africa, India and south east Asia.
Four species are endemic to Asia. These are Hibiscus furcatus, which is native to India and Thailand, Hibiscus hispidissimus (8x; BG-- or BGWZ), which is an Indian species, also naturalised in South Africa, Hibiscus hoshiarpurensis, of northwest India, and Hibiscus radiatus (4x; AB), which is a recent allopolyploid hybrid between Hibiscus cannabinus and Hibiscus surratensis, originating in India, but now widely cultivated in the Old and New World tropics. Some African species (Hibiscus cannabinus, Hibiscus mastersianus, Hibiscus sabdariffa) are naturalised in India.
Australia has 33 species, including the pantropical Hibiscus diversifolius and the naturalised Hibiscus sabdariffa. Hibiscus meraukensis (6x; GJV) is found in northern Australia, New Guinea and the Moluccas. The 30 endemic species are Hibiscus aneuthe, Hibiscus aphelus (6x), Hibiscus arnhemensis (6x; GJV), Hibiscus bacalusius, Hibiscus byrnesii (6x; GJV), Hibiscus divaricatus (6x; GJV), Hibiscus fallax, Hibiscus forsteri, Hibiscus fryxellii (including var. mollis) (6x; GJV), Hibiscus graniticus, Hibiscus heterophyllus (6x), Hibiscus inimicus, Hibsicus kenneallyi, Hibiscus kirstyae, Hibiscus marenitensis (6x), Hibiscus menzeliae (6x; GJV), Hibiscus minutibracteolus (6x), Hibiscus petherickii, Hibiscus reflexus (6x), Hibiscus riceae, Hibiscus sankowskyorum, Hibiscus saponarius. Hibiscus splendens (6x; GJV), Hibiscus squarrulosus, Hibiscus stewartii, Hibiscus superbus (6x), Hibiscus symonii (6x; GJV), Hibiscus thegaleus, Hibiscus townsvillensis and Hibiscus zonatus (including Hibiscus mustiae). The status of Hibiscus sp. Barambah Creek and Hibiscus sp. Glen Geddes remains unclear.
5 species are found in the Pacific Islands, 3 are of which are endemic: Hibiscus australensis to the Tubuai or Austral Islands;. Hibiscus brackenridgei (8x; GbJVU) is native to Hawaii, where it is the official state flower; and Hibiscus fijiensis (10x: CDEG-) to Fiji. Hibiscus furcellatus (4x: GP) is native to Hawaii, and to much of the Americas. Hibiscus diversifolius (8x; CDEG) has a pantropical distribution; in the Pacific it is found in New Caledonia, Vanuatu, Fiji, Niue, Norfolk and Lord Howe Islands, New Zealand, Revillagigedo and the Galapagos Islands. [4]
Hibiscus brackenridgei is divided into three subspecies: brackenridgei, molokaianus and mokuleianus. An extinct population on Kauai may represent a 4th subspecies. [4]
Additional species are recognised in recent checklists for Argentina [] (Hibiscus urticifolius) and the Guianas [] (Hibiscus varians). However, although Hibiscus urticifolius was originally described from southern Brasil it is omitted from the recent Brasilian checklist [].
With over a 100 species there are over 5,000 potential hybrid combinations, excluding multi-species hybrids, and only a small proportion have been attempted, never mind achieved. This still results in a considerable number of reported hybrids in Hibiscus section Furcaria. Some of these, spontaneously, or through colchicine treatment, have given rise to allopolyploids.
As Hibiscus cannabinus and Hibiscus sabdariffa are crop species agricultural cultivars of these species exist. There are also ornamental cultivars of Hibiscus acetosella, and of species and hybrids of the Australian native species.
References
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