The genus Thunbergia in southern Africa *

The genus Thunbergia Retz. in southern Africa is revised and eleven species are recognized.

Flower bracts 2, sessile, opposite, caducous or persistent, enlarged sometimes to protect fruit, ovate, boat-shaped, keeled, base cordate.Calyx persistent, connate at the base, usually with 10-16 subuliform lobes, unequal in length.Corolla gamopetalous, tube cylindric at base, infundibuliform in the upper part; 5-lobed, lobes obovate or sometimes nearly triangular, contorted; inner and outer surface of lobes and outer surface of tube white, shades of yellow, orange or purplish-blue; inner surface of tube shades of yellow, yellowish green or dark purplish black; one-celled trichomes sometimes present, as well as stipitate glands.Stamens 4; included, didynamous, inserted at the base of the infundibuliform part o f the tube.Filaments broad at the base, linear dorsifixed, connective ending in an apiculum, multicellular hairs present at base.Anthers 2-thecous; thecae of long stamens equal, spurred, with trichomes nearly along the whole length of the cleft and concentrated at the base; thecae of short stamens unequal, the longest one with trichomes along the whole length of the cleft, spurred, the other one with trichomes only at the base, spurs absent o r rudimentary; spurs un branched in exceptional cases, branched at apex (Fig. 2).Gynoecium superior, included, ovary 2-locular with two axile ovules per locule; style cylindric; stigma funnel-shaped or 2-lobed, usually with one lobe above the other (Fig. 3).Disc present, annular, fleshy.Fruit a capsule, globose, beaked, loculicidal dehiscent, trichomes present o r absent; fruit stalk, sometimes swollen (Fig. 4).Seed semi-globose with a cavity on the side of the hilum; testa brown to greyish black, pubescent, trichomes homogeneously distributed or adhering to form different patterns on the testa (Figs 5 & 6).
In 1773 Montin described the genus Thunbergia in Rubiaceae.In 1780 Raetzius, aware of Thunbergia M ontin, used the same generic name for describing species of Acanthaceae collected by Thunberg at the Cape, hence Thunbergia Retz.was a later homonym and therefore illegitimate.L ater authors such as the younger Linnaeus (1781) did not attribute Thunber gia to Retzius, and Lindau (1893) and C.B. Clarke (1912) actually attributed the name to Linnaeus fil.
Fortunately the problem has been resolved by* conservation of Thunbergia Retz.against Thunbergia Montin with T. capensis Retz.as the type species of the conserved nam e(IC B N ,p. 396,1978).
The presence of conspicuously large bracts concealing the saucer-shaped calyx with its tooth like lobes, panduriform glandular hairs, the structu re of the corolla, the fruit being a globose capsule with a prominent, ensiform beak and the absence of retinacula are important features characterizing the genus Thunbergia.
Found in shade along the margins of forests and woodland or pine plantations, rarely in direct sunlight.Recorded from the Transkei, Natal, Swaziland, Transvaal and northwards to Kenya (Fig. 7).
T. natalensis is characterized by its growth form, purplish blue corolla, the curved spurs of the anthers and a funnel-shaped stigma.The species flowers from October to March.
The 'Natal Blue Bell' is found growing in gardens.
T. venosa is found in grassland where it occurs in open sunlight.The species is endemic in Natal (Fig. 8).It is distinguished from related taxa by its single stem with slender, sessile leaves, densely crowded in the upper part.The species flowers from September to April.
A decoction obtained from the minced roots of T. venosa is used by the Zulu people as a love-potion (Hulme, 1954).
T. atriplicifolia is found as a subordinate species in grassland where it flourishes in both loam and sandy soil.The species has a wide distribution, occurring in the Transvaal, Swaziland, Natal, Transkei and the Cape Province (Fig. 9).The species is very variable and occurs in different habitats: it is not only found inland, but also in grassveld close to the sea.Lindau (1898) who described T. bachmannii, T. xanthotricha and T. flavohirta mentions that these three species might be varieties o f one species, namely T. atriplicifolia and that they needed further investigation.Clarke (1912) in his revision o f the genus also indicates that it is an open question whether it is not better to regard the species T. bachmannii, T. xanthotricha and T. aspera as conspecific.In 1864 Anderson cited T. aspera as a synonym of T. atriplicifolia.Clarke (1912) used leaf shape, pubescence of the style and the form of the flower bracts, to distinguish T. atriplicifolia, T. aspera, T. cordibracteolata, T. bachmannii, T. hirtistyla and T. xanthotricha.The range of variation within this species complex is very marked.However, as extreme forms are linked by numerous intermediates no formal subdivisions are upheld here.Variation of the leaf blade within the species is shown on Fig. 10 According to Batten & Bokelmann (1966), the Xhosa people prepare a love-potion from the roots and leaves of the plants and W att & Breyer-Brandwijk (1962) mention that the leaves of T. atriplicifolia are used to make a hairwash.The .species is known as 'Natal Primrose' or 'Cape Primrose'.
T. capensis flourishes not only on sandy soil in grassland along the coast, but occurs also in stony soil of false fynbos as found in the Ecca Pass area.7'.capensis is endemic to the Cape Province and the Transkei (Fig. 11).
The plant is characterized by broadly ovate leaves with apices acute, obtuse or emarginate, the greenish yellow colour of the corolla and the anther thecae not being spurred.The flowering period of T. capensis is from October to April.
The species is suspected of hybridizing with T. atriplicifolia where their areas overlap (see T. atriplicifolia).Specimens of T. capensis with erect stems and flowers nearly double the normal size were collected near Hayes railway halt between Grahamstown and Port Alfred.On investigation they were found to have a triploid chromosome number.
T. purpurata is usually found along the margins of forests or in open parts in the tropical coastal forests.The species occurs only along the coast o f Natal and the Transkei as far south as the Kei River (Fig. 11).
It is distinguished from related species by its dark green leaves with conspicuously dark purplish veins on the under surface.The species flowers from November to March.
In 1827 H ooker published a drawing and a description of T. angulata Hils.& Boj.ex H ook., endemic in Madagascar, with a separate drawing of an anther that was from a Thunbergia species o f the Cape (Clarke, 1912).T. angulata is not found along the coast of southern Africa as m aintained by Hooker and also Anderson (1864) and Lindau (1893).The anther could, according to Clarke (1912), belong to T. purpurata described later on.The two species can easily be distinguished by the anther thecae which, in T. purpurata, are not spurred or weakly so, the leaf base of T. purpurata is hastate and not cordate, whereas the corolla of the species is white and not purple.Natal Plants 4: t.340 (1906); Wood in Trans.S. Afr. phil. Soc. 18: 204 (1909);Bews, FI. Natal & Zululand 192 (1921);Ross, FI. Natal 323 (1972).Type: Natal, Backbeach, D urban, Bachmann 1265 (Bt); Inyesane, Wood 4015 (N H , lecto.!; PRE, photo!).
The specific epithet pondoensis refers to the area, Pondoland (eastern part of the Transkei), but the species is not known from this area.The locality given by Clarke (1912) andW ood (1909) for Wood 4015, the lectotype, is Entum eni in Natal and not Inyesane as stated on the label of the specimen in NH.
Woodland, thornveld and grassland are natural habitats of T. neglecta.The plants usually occur in loam soil under trees and shrubs, but they do grow in direct sunlight between the trees and shrubs.T. neglecta is the only species of the genus Thunbergia occurring in the Orange Free State.It is also found in Botswana, Transvaal, Swaziland, Natal and the Cape Province (Fig. 12).
T. amoena occurs mainly along the margins of inland forests, but is also found along the margins of pine plantations and against rocky slopes where the forest changes to mountain grassland.It forms dense mats on the pine needles and rocks.T. amoena is endemic to the Transvaal (Fig. 13).
T. dregeana is found along streams and the margins of forests.The species occurs along the eastern coast of Natal and in the Cape Province as far south as the Gamtoos River (Fig. 13).
This species is characterized by a dull orangeyellow corolla with large lobes.It flowers from November to February.A strong decoction o f T. dregeana is used by the Zulu people as a remedy for venereal diseases (W att & Breyer-Brandwijk, 1962).Medley W ood (1902) mentions that local Asian women, like the Zulus, prepare a hairwash from the green fruits of T. dregeana.Corolla with inner and outer surface of lobes and outer surface of tube orange, inner surface of tube dark purplish black with white stripes at base; lobes 7 ,5 -1 3 ,5 x 1 1 -2 0 mm.Filaments 4 -5 ,7 mm long; anther thecae 3,6-4,6 mm long.Style 8,5 -11 mm long; stipitate glands present.Fruits 15 -18 mm long, globose base 7 ,5 -9 mm in diam eter; stalk (13-) 35 -64 mm long.Seed brown; some trichomes adhere to form wing-like protuberances; 2 ,4 -4 mm in diameter.

Thunbergia alata
T. alata is found along margins of forests where it is humid and the soil is humic, but also in open sunlight and more sandy soil.The species is indigenous to east Africa and occurs southwards to the eastern Transvaal and Natal (Fig. 14).
The species is characterized by the colour o f the corolla, winged petioles and the trichomes of the seed surface forming wing-like protuberances.T. alata flowers nearly the whole year round.T. alata is known as the Black-eyed Susan, because the inner surface of the corolla tube which is usually a purplish black colour, surrounded by the bright orange corolla lobes, reminds one of an eye.
It is cultivated in many tropical and subtropical parts of the world where the species often becomes naturalized.Different colour variations occur.In 1839 Paxton described a species known as T. aurantiaca, darker in colour and with larger flowers than T. alata.The author mentions that the seed of this species cultivated in England was from the Cape of Good Hope.As far as known, only the form with flowers having an orange corolla with the inner surface o f the corolla tube purplish black, is indigenous in southern Africa.Invisible ultra violet patterns on the fresh corolla of T. alata but visible as fluorescent patterns in pressed herbarium speci mens, were observed by Eisner (1973).
T. aurea occurs in three of the veld types distinguished by Giess (1971) in South West Africa/Namibia, namely: (i) mountain savanna and karst veld, (ii) thorn savanna; and (iii) tree savanna and dry forest.It is found in sandy soil under trees and shrubs o r against the slopes of dolomite hills.The species is also known from Botswana and the Transvaal (Fig. 14).
The species is characterized by its small size and the dull orange-yellow colour of the corolla, a winged petiole like T. alata and the trichomes o f the seed surface adhering to form papillae-like protube rances.T. aurea flowers from January to March.
According to De W inter (specimen no.4159) the leaves of T. aurea are used as spinach, and Rodin (specimen no.9105) mentions that the leaves are dried and then boiled.The decoction obtained, is used as a remedy against coughing.T. capensis Retz.var.grandiflora Nees in DC., Prodr. 11: 55 (1847): the type has not been found.
T. stenophylla C. B. Cl. in FI. Cap. 5,1: 6 (1912): the type specimen in the British Museum (Natural History) is very poor and throws no light on the identity of the taxon.
Fig. 5.-Part of the seed surface of Thunbergia pondoemis where the trichomes adhere to form ridges, x 42.

Fig, 6 .
Fig, 6.-Part of the seed surface of Thunbergia aurca with patches where no trichomes occur, x 56.
. W here the distribution areas of Thunbergia atriplicifolia and T. capensis overlap, plants occur pointing to hybridization o f gene-flow between the two species.Such specimens were in the past identified either as T. atriplicifolia or T. capensis.The leaves of the plants look like those of T. capensis only larger, whereas the flowers resemble those of T. atriplicifolia.The following specimens are examples of such intermediate plants: T ranskei.-3228(Butterworth): M azeppa Bay (-B C ), Story 4463 (PR E ); Kei Mouth ( -C B ) , Flanagan 552 (G R A , PR E, SAM); Bulura River Mouth ( -C C ) , Acocks 15799 (PR E).
Calyx with sessile and stipitate glands.