Prior to the application of DNA sequencing techniques to the taxonomy of Hibiscus and allies I expected that a few genera would be found to be nested in Hibiscus, and this would be resolved by removing parts of Hibiscus so that each genus has a common ancestor to the exclusion of other genera. Instead the work of Pfeil et al6 found that some segregate genera were not only nested within Hibiscus, but nested within particular sections of Hibiscus. Additionally species from the tribes Decaschistieae and Malvavisceae (Ureneae) were also found to be deeply nested in Hibiscus, suggesting that the whole of these tribes are descended from ancestors which would be placed in Hibiscus. These results mean that the appropriate modifications to the classification of hibiscuses and allied plants are not obvious; merging them all into one genus would produce a genus with well in excess of 500 species with few or no diagnostic characteristics other than DNA sequence traits; while retaining the currently recognized genera would lead to breaking up Hibiscus into many genera lacking morphological distinctiveness.
There is as yet insufficient sequence data on which to base a complete treatment
of Hibiscus and allies; not only have not all species been included with
the study, but also not all sections and segregate and allied genera have been
sampled, so even if we were to boldly assume that all sections and genera are
correctly identified as natural groups and none are nested within another, we
are lacking information on some relationships.
Other segregate genera, such as Lagunaria, Alyogyne and Radyera, were found to be distantly related to Hibiscus6.
The Hibiscus sensu lato clade can be characterized by the presence of 5-celled ovaries and fruits (6-10-celled in Decaschistia), the fruits usually being capsules which split lengthwise along the middle of the cells, or schizocarps; by the presence of reduced staminodes in the form of an antherless, often toothed, apex to the staminal column; and by the presence of 5 or 10 style-branches (6-10 in Decaschistia) each terminated by globe-like stigmas. When the fruit is a schizocarp each cell is single seeded.
Within the data of Pfeil et al6 6 groups can be recognized within Hibiscus. There follows an overview of the sections of Hibiscus based on these 6 groups. Note that further research may identify additional groups among unsampled species and sections, and among segregate and allied genera. Sections Ketmia and Bombicella are not natural groups, and would be revised in a full treat-ment of Hibiscus. In particular the 4 sampled species of Ketmia fell into 3 different groups, and I don't know where the main body of Ketmia, if there is one, would fall.
Group 1: This group contains a single species, which is part of section Ketmia. This is H. pentaphyllus, from southern and eastern Africa, India, and northern Australia. H. pentaphyllus has long flower-stalks, large flowers with a flat epicalyx of 8 long narrow bracteoles, and a spreading calyx composed of long acuminate sepals, and deeply 3-5-lobed leaves7.
Group 2: This group consists of section Calyphylli plus the species H. dongolensis, which is currently placed in section Ketmia. The raw DNA sequence data only weakly associates H. dongolensis with section Calyphylli, but the pattern of insertions and deletions in the sequences suggest a common ancestry, whether a single polytypic species or a reticulate hybrid grouping.
These species are found in eastern and southern Africa and in Madagascar. H. calyphyllus (also known as H. calycinus and H. rockii) is naturalized in Hawaii. The species of section Calyphylli have cordate, ovate, toothed, leaves, which unlobed, or weakly-lobed. The flowers are borne on short stalks. Pfeil6 et al sampled two species of section Calyphylli (H. calyphyllus, H. ludwigii), but I suspect from other sources7,8,9,10 that H. macranthus, H. lunariifolius and H. platycalyx also belong here.
Group 3: This group is a moderately species rich and diverse group consisting of sections Bombicella, Hibiscus, and Lilibiscus, and also the Macrostelia grandiflora complex and Alyogyne cravenii.
Section Bombicella has a pan-tropical distribution. There are 20 or more species, including H. cardiophyllus of North America, H. phoeniceus of the Caribbean and Latin America, H. micranthus of East Africa, H. pedunculatus of South Africa, H. hirtus of India and H. sturtii of Australia. They are generally found in drier regions, but H. peralbus of the Kimberley rainforests of Australia and H. insularis of Philip Island are found in wetter regions.
Section Hibiscus contains the hardy shrub hibiscuses (known as Rose of Sharon in North America). These are two species, H. syriacus and H. sinosyriacus, from Korea and northern China. There are about 100 cultivars in all11. The flowers are medium sized. The leaves are of uniform shape.
Section Lilibiscus contains the cultivated tropical hibiscuses, including H. rosa-sinensis (the Rose of China) [Left photo: Stewart R. Hinsley © 2003). There are about a dozen species, found in humid parts of the Indo-Pacific region from the coast of East Africa to Hawaii. Being extensively cultivated and hybridized the natural distribution and validity of the various species is uncertain. The flowers are generally large and somewhat asymmetrical. The epicalyx typic-ally has around 6-9 narrowly triangular epicalyx bracts. The leaves are usually of uniform shape. H. schizopetalus of East Africa is dis-tinctive in its split petals and small (almost unnoticeable) epicalyx [Right photo: Coleen Keena © 2003).
Section Spatula is named for its spoon-shaped bracteoles. It includes the Australian H. normanii. The South American H. spathulatus also has spoon-shaped bracteoles12.
Alyogyne cravenii is a localized species from northern Australia. It was found by Pfeil et al6 to be misplaced in the genus Alyogyne and to agree with section Bombicella in both DNA and morphological traits.
The Macrostelia grandiflora complex is a group of 3 taxa (2 currently classified as subspecies of M. grandiflora and the 3rd not formally described) from northern Queensland. These were found by Pfeil et al6 to be closely related to A. cravenii and some species of section Bombicella. The petals of Macrostelia have long claws which are fused to the staminal column for half their length. The morphological evidence13 for associating the M. grandiflora complex with the 3 Malagasy species of Macrostelia consists of more than the long petal claws and is convincing, but the distribution casts doubt on this. Hence whether the Malagasy species of Macrostelia fall into group 3, or even within Hibiscus, is unknown.
Group 4: This is the largest and most diverse group. The work of Pfeil et al6,19 and Small14 shows it to contain elements of section Ketmia, sections Striati, Solandra, Trionum, Panduriformes, Muenchhusia and Venusti; and the segregate genera Abelmoschus, Fioria and Kosteletzkya. Additionally 4 species of the former tribe Malvavisceae (or Ureneae) fall in here, from which we are led to the tentative conclusion that the whole of that 'tribe' belongs to this group, and close to Fioria.
The group is predominantly composed of herbs and small shrubs. The sole species of section Solandra sampled by Pfeil et al6, the African H. schinzii, was found by them to be closely related to two African species currently placed in section Ketmia, these being H. engleri and H. physaloides. The Indian H. solandra usually lacks bracteoles15.
Section Striati is a small group of American species, including H. striatus and H. trilobus.
Section Trionum may be a monotypic section. Its titular species, H. trionum, is an annual herb. The lower leaves are rounded; the upper leaves are deeply 3-5-lobed. In fruit the calyx has a distinctive inflated appearance, which is shared with sections Clypeati and Striati.
The titular species of section Panduriformes, H. panduriformis has large yellow flowers, sometimes with spoon-shaped bracteoles (with longer 'handles' than in section Spatula) and scarcely divided or undivided, rounded, leaves. It is found in Africa, the Mascarenes, India and Australia.
Section Muenchhusia is a close group of 5 species, the American Rose-Mallows, mostly from the eastern USA, but extending into Canada's Ontario Peninsula, and to California in the western USA. These are large-flowered perennial herbs. They, and especially their hybrids and cultivars, are grown as ornamentals.
Section Venusti is a group of a half a dozen or more species of shrubby hibiscuses from east Asia. The best known is H. mutabilis, grown in North America as the Confederate Rose.
Genus (or section) Abelmoschus is a group of about 15 species from the Old World tropics. They have elongated fruits. The calyx partially encloses the corolla in flower, but splits asymmetrically to reveal the petals. The calyx, and usually the epicalyx, are caducuous, i.e. are not retained with the fruit. Okra, A. esculentus, is the most important food crop within the mallow family. Other species are also cultivated as fruits, vegetables or for fibre.
Genus Fioria (section Pterocarpus) has winged fruits. This genus is exempli-fied by F. vitifolia, which has distinctive vine-shaped leaves. There is dis-agreement as to whether there is just the one, variable, species, or whether there are several species of the genus.
Genus Kosteletzkya (section Pentaspermum) approaches Fioria in possessing winged or less commonly angled fruits, and approaches Malvavisceae in the cells of the fruit being single-seeded. It consists of 17 species5, mostly from tropical America, and to a lesser extent, Africa, but also with species in the eastern USA, southern Europe, south west Asia, and Malesia.
The old Malvavisceae is characterized by fruits being 5-celled schizocarps or berries, each cell being single-seeded, and the flower having 10 style branches, i.e. 2 for each ovary-cell. It contains as many species (about 300) as the rest of Hibiscus sensu lato. Bayer5 recognizes 8 genera here; Urena, Malachra, Peltaea, Phragmocarpidium, Rojasimalva, Pavonia, Malvaviscus and Anotea. Pavonia is by far the most diverse and species-rich of these genera. This group is mostly found in the Americas, but Urena is pantropical, Malachra extends to the Old World Tropics and some 25 species of Pavonia are found in the Old World Tropics, including 2 species in Australia.
Urena has spiny, burr-like, fruits and abaxial leaf nectaries. Malachra has bracts enclosing inflorescences, but lacks epicalyces. Peltaea has bracts and epicalyces. Rojasimalva is similar to Peltaea, but has mericarps with a spine longer than the body. Phragmocarpidium has 2-celled mericarps, the lower cell being empty. Malvaviscus has red or white berries, and red flowers with basally auriculate petals. Anotea has blue-black berries and yellow flowers. Pavonia contains the species with none of these specializations, and may well not be monophyletic. Groups within Pavonia have been given generic rank, such as Triplochlamys (with a double, petaloid, epicalyx), Goethea (with flowers borne on or close to the branches), and Blanchestiastrum and Codonochlamys (with fewer bracteoles)16.
Group 5: This group is species-rich, but relatively stereotyped. It consists of section Furcaria and genus Decaschistia.
Section Furcaria consists of comfortably over 100 species17 of erect-, often prickly-stemmed herbs and shrubs found throughout the tropics. Nectaries are borne on veins on the calyx lobes and the lower portions of the leaves. The lower leaves are typically lobed, often deeply so, and the upper leaves less lobed or unlobed. The bracteoles of the epicalyx are usually forked or with a distinct terminal appendage. There are 10 diploid species (9 African, 1 American), and many polyploid species of hybrid origin, involving those 10, and other, now extinct, diploid species.
Decaschistia is a genus of approaching a score or species from India, South East Asia, southern China and northern Australia. They are not known from Indonesia. They are distinguished by an increase in the number of ovary and fruit cells and the number of style arms5,15. Pfeil et al6,19 found that two sampled Australian species were jointly nested in section Furcaria. The similarities between the Asian and Australian species are sufficient13 to tentatively include the whole genus within group 5.
Group 6: This group consists of the genus Talipariti18, recruited out of section Azanzae, and the genus Papuodendron, which was originally placed in tribe Durioneae and family Bombacaceae. Historically some species of Thespesia were misplaced in section Azanzae. The genus Wercklea was not sampled, but it has been speculated18 that it may be closely allied to Talipariti.
This group is the sister group to group 5. It shares with it the characters of leaf and calyx nectaries. It differs in being composed of arborescent species, the leaves being usually unlobed, and of uniform shape on a single plant.
Talipariti is a genus of 22 species with a distribution centered on south east Asia, but also found in tropical America, tropical Africa, India, Japan and Pacific Islands. They have a number of distinguishing traits, including the presence of stem-clasping stipules. T. tiliaceum is widely distributed along tropical shores as a mangrove associate and is also grown as an ornamental. T. elatum is grown in a small way as a timber tree.
Papuodendron is a genus of 2 species of tree from New Guinea. DNA sequence data places them close to Talipariti19. They differ from Talipariti in the absence of stem-clasping stipules, in the surfaces of the plant being scaly rather than (usually) hairy, and in lacking staminodes.
Wercklea is a genus of 13 species of herbs, shrubs and trees from tropical America.
Other Sections and Species: Apart from the sections listed above there are also at least sections Aristivalvus, Clypeati, Columnaris, Bombycidendron, Parapavonia, Pentacalycinus, and Trionastrum, for each of which I am aware of a single species. (However, I have noted 70 species for which I have seen either no sectional affiliation, or have only seen a sectional affiliation in a work so old that the affiliation can't be taken as correct for a current classification.) Furthermore, some species were placed in section Azanzae, but were not transferred to genus Talipariti18. Due to the rules of biological nomenclature they cannot be classified in section Azanzae, and may be currently in a classificational limbo. It is not clear whether they should be retained in group 6.
H. sororius, the type species of section Trionastrum, has bracteoles with a kidney-shaped appendage at the apex.
Other Genera: Other genera related to Hibiscus are the Hawaiian Hibisca-delphus, the Senra of East Africa, Arabia and Pakistan, the east African Symphyochlamys, the Malagasy Megistostegium, Perrierophytum, Humbertiella, Helicteropsis and Humbertianthus, and the south east Asian Cenocentrum. Many of these have not been studied by DNA sequencing and for the others the DNA results are unclear19. Senra appears to fall into group 4, and Megistostegium, Perrierophytum and Humbertiella to lie on the fringes of Hibiscus. Given the results obtained with other genera in Hibisceae we have to consider the possibility that any of these might be nested within Hibiscus. In particular Hibiscadelphus is in some ways reminiscent of section Lilibiscus, and Cenocentrum of Decaschistia.
Section Bombicella: The plants shown above are plants from Section Bombicella that are in cultivation. They range from being on a weed list, H. pedunculatus, to being almost extinct in the wild, H. insularis. There are plants from Africa, H. pedunculatus, Australia, H. sturtii, and U.S.A., H. cardiophyllus (martianus). There is a great variation in size, with H. sturtii reaching only 12" (30 cm) while H. insularis (12 feet, 4 m) makes a good salt tolerant hedge. H. hirtus is listed as a crop while H. insularis is grown for its blooms which start pale lemon and turn a light rose colour as they age. While the blooms of a number of species such as H. sturtii, H. hirtus and H. pedunculatus are small, the plants bloom freely.
HIBISCUS GALLERY BY STEWART ROBERT HINSLEY
Section Calyphylli: Hibiscus calyphyllus is the most readily available hibiscus in this Section although Hibiscus ludwigii is also in cultivation. H. calyphyllus is a perennial herb from Africa reaching 1-2 m (3-6'). The growth can be prostrate and sprawling. The attractive 12-15 cm (5-6") flowers are bright yellow with a dark eye. The flowers are produced prolifically over a long period in the warmer months. The plant is used in rockeries and performs well in pots. It can be grown from cuttings. Its heavy flowering, heavy seed production and ability to cope with a range of conditions, such as reduced moisture, means that this plant can become invasive. In garden conditions, it may produce roots all along the stems and be hard to remove.
HIBISCUS GALLERY BY STEWART ROBERT HINSLEY
trionum: H. trionum is an annual hibiscus
in this Section. It has been called 'Flower of an hour' because its blooms die
quickly. However, forms have been developed for horticulture, e.g. 'Sunny Day',
'Fantasia', where the blooms last longer. The flowers are carried in huge numbers
over the entire plant for all of the summer and well into autumn. Unfortunately,
the ornamental nature of this plant, the profuse flowering and seeding and the
ability to cope with a wide range of conditions, means this plant is now a pest
species. Even two forms found in Australia, H. trionum var. trionum and H. trionum
var. vesicarius are shown in lists of weeds at:
HIBISCUS GALLERY BY STEWART ROBERT HINSLEY
Section Ketmia: Hibiscus pentaphyllus is one of the species in this Section. It is an erect annual shrub to 2 m (6') high. It occurs from southern and eastern Africa, India, and across northern Australia along rivers and on floodplains. Being an annual, the seeds germinate after the first rains of the wet season and then plants grow rapidly. The flowers, 6-8 cm (2 ½-3 ¼") are yellow with a dark centre, aging to a deep pink. The seed pod of Hibiscus pentaphyllus is perhaps its most unusual feature. The calyx and epicalyx that can be seen above remain attached making the dried seed pod a most unusual shape. This species makes a good container plant, flowering well and setting seed when grown in a pot.
Spatula: Hibiscus normanii is in
this Section. While it is not well known and not readily available, it was illustrated
when Joseph Banks and his party collected specimens of it during the voyage of
HMB Endeavour in 1770. It is illustrated in Banks Florilegium and a copy of this
print can be seen at:
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