The genus Solanum (Solanaceae) in southern Africa: subgenus Leptostemonum, the introduced sections Acanthophora and Torva

In the genus Solanum L. (Solanaceae), subgenus Leptostemonum (Dunal) Bitter, section Acanthophora Dunal has four representatives in the Flora of southern Africa region (South Africa. Lesotho, Swaziland, Namibia. Botswana), namely S. aculeatissimum Jacq.. S. capsicoides Allioni. S. mammosum L. (cultivated only) and S. viarum Dunal. Section Ton a Nees has two representatives in southern Africa, namely 5. chnsotriclium Schltdl. (5. hispidum auctt. non Pers.) and 5. ton um Sw.; both are naturalized weeds. Solanum capsicoides, S. viarum and 5. ton um have not been listed before for southern Africa. All are introduced species native to the New World. Descriptions, discussions, illustrations and distribution maps of the naturalized species are presented, as well as keys to the species of both sections.


INTRODUCTION
In the genus Solanum L.. the prickly subgenus Lepto stemonum (Dunal) Bitter is represented by eight sections in southern Africa. Two sections contain only indigenous taxa. one section contains mainly indigenous taxa, and the remaining sections have only introduced species. Section Acanthophora Dunal is represented by four species in southern Africa. All are originally from the Americas, namely the rather common and widespread weed S. aculeatissimum. the relatively rare weed S. cap sicoides, the cultivated ornamental S. mammosum. and S. viarum which is becoming a fairly common weed in KwaZulu-Natal and neighbouring areas. S. capsicoides and S. viarum have not been listed belore for southern Africa (Welman 1993). Section Torva Nees is represent ed by two species in southern Africa; both are originally from the Americas. S. chry sotrichum is so far naturalized only in Eastern Cape, while S. ton um is confined to a fairly small area north of Durban. KwaZulu-Natal.
Detailed descriptions and discussions are given for both sections and all six species, together with keys, illustra tions and distribution maps. S. mammosum. being culti vated only, has no distribution map.
Description (based on Nee 1991) Small shrubs. 0.3-3.0 m tall, sprawling or more often erect and few-branched. annuals or short-lived perenni als. heavily armed with straight acicular (needle-shaped) prickles, in some species stems with additional robust recurved prickles from enlarged compressed bases. Stems usually glandular-puberulent. often also eglandular-pilose w ith few -celled, simple hairs. Leaves petiolate, alternate or usually geminate, with one about twice the size of the other: blades usually ovate to orbicular and w ith 2-4 pairs of lobes, or repand. coarsely and irregu larly toothed, membranous, spiny along main veins above and below, usually glandular-puberulent above and usually also eglandular-pilose with simple fewcelled hairs, these sometimes with vestigial rays at base, below with simple hairs and sessile few-rayed stellate hairs (these lacking in S. capsicoides). Inflorescences lat eral. simple or few -branched. sessile or shortly peduncu late. remote from leaves, axis often spiny: flowers few to many, fewer than half fertile, often only lowest fertile in large-fruited species. Calyx seldom much accrescent: lobes triangular to linear. Corolla w hite. yellow ish. green ish or blue-purple, glandular and pilose on outside, stel late, without interstitial pleating. Ovary glabrous or minutely stipitate-glandular, puberulent in few species with simple hairs that drop off early. Fruit usually glo bose, small to large, strongly dark green and pale green marbled when young, yellowish, orange or reddish at maturity, glabrous at maturity, exocarp ± tough, mesocarp juicy, in some species becoming dry at full maturi ty, placentae simply columnar, divided or variously intruded, the fruit becoming effectively or completely unilocular at maturity. Seeds numerous, subreniform to orbicular, seed coat closely investing endosperm or extending around periphery of seed into a flattened wing.

Distribution and ecology
According to Whalen (1984), section Acanthophora occurs throughout the American tropics except in Amazonian Brazil; it is most diverse in the northern Andes and in southeastern Brazil. About 20 species grow in open savanna and disturbed sites. Several species are established in the Old World tropics. Nee (1979) noted that this section, in common with almost all groups of Solanum, has great weedy tenden cies; the species are found in areas of high light intensi ties and also where the natural vegetation has been dis turbed. Under natural circumstances, landslides, eroded stream banks and forest openings provide suitable habi tats. Man's agricultural and industrial practices are still expanding the ranges of numerous species of Solanum. The succulent berries of many species are popular with birds and ensure seed dispersal.
Taxonomy Dunal (1813) appropriately named this group of prickly species section Acanthophora (thorn-bearing). In 1923, Bitter referred to the characteristic hairs of this section in the name Simplicipilum. However. Dunal's name for this section must take precedence.
In 1972, D'Arcy elevated subsection Lasiocarpum Dunal of section Acanthophora to section Lasiocarpum (Dunal) D'Arcy, with S. lasiocarpum Dunal as type species. Section Acanthophora can be distinguished from section Lasiocarpum by the lack of stellate hairs on the ovaries, the more general coverage with multi-celled simple hairs and the less substantial habit (Jaeger 1985). Section Lasiocarpum is indigenous to South America and no representatives have so far been recorded from southern Africa, though a few species are naturalized and/or cultivated in East Africa; see Jaeger (1985). Whalen (1984) placed S. aculeatissimum, S. capsicoides, S. mammosum and S. via rum in his 5. mammosum Group.

Microscope studies
Section Acanthophora has distinctive simple hairs that are long, multicelled, uniseriate. shiny and translu cent. These simple hairs are identical with the central ray of the stellate hairs on the same plant; the latter often only present on juvenile plants or leaves. During evolu tion the basal side rays of the stellate hairs have appar ently disappeared. Single-celled simple hairs, often gland-tipped, may also occur on the upper surface of the leaf as well as elsewhere on the plant (Nee 1979).

Diagnostic characters
According to Whalen (1984). the S. mammosum Group of species is distinguished by an essentially herbaceous habit, difoliate-geminate sympodia. vestiture of predom inantly simple hairs, variously lobed or dentate, prickly leaves, lateral, often simple inflorescences, stelliform corollas and dryish, glabrous berries. Nee (1979) stated that section Acanthophora, as a member of the prickly subgenus Leptostemonum (Dunal) Bitter, deserves its name; all the species are heavily armed with sharp, slender prickles and some species have stouter, broad-based prickles as well. He defined the section by the combination of the upper leaf surface bearing only simple hairs, glabrous fruit and the non-to only slightly accrescent calyx.
This section can be divided into two subsections based on the seed morphology (Nee 1979). One subsec tion, with seeds that do not differ much from those of almost all other Solanum species, includes S. aculeatissi mum, S. mammosum and S. via rum. The other subsection is characterized by seeds surrounded by a broad, flat tened margin or wing, a character unique in Solanum. This subsection is probably monophyletic and includes S. capsicoides. The evolutionary significance of the winged seed is not clear; it could aid in wind or water dispersal.

Sex forms and branching
Whalen & Costich (1986) described section Acan thophora as weakly to strongly andromonoecious; having both perfect and male flowers, but no female flowers. Species of this section have some short-styled flowers, and are self-compatible. The fruits are small to large; it was found that andromonoecy in section Acanthophora is most strongly developed in large-fruited species. Child (1979) and Child & Lester (1991) studied the branching patterns in the Solanaceae. All sections of the subgenus Leptostemonum have 2-or 3-foliate sympodial units often with the subtending leaf paired with the small er first leaf of the daughter shoot (anisophyllous geminate sympodia). Section Acanthophora has mostly simple few-flowered inflorescences with only the basalmost flower and/or the few proximal flowers of the subsidiary inflorescence hermaphrodite; the distal flowers are usual ly smaller, brachystylous or short-styled (andromonoe cious ;Symon 1979) and are often inserted with a spatial gap from the hermaphrodite flowers. Species with prick ly calyces in the hermaphrodite flowers usually have unarmed, functionally male, brachystylous flowers. Nee (1991) noted that this section contains a number of promising candidates tor screening tor alkaloids.

Note
Annual, sparsely branched herb or undershrub up to 1.5 m high, pubescence highly variable, dense to sparse (plant rarely nearly glabrous). Stems tinged purple and green, rarely densely pubescent, with simple, uniseriate. multicellular hairs of unequal lengths, up to 4 mm long, heavily armed with many slender, acicular, straight, spreading or slightlv reflexed prickles up to 12 mm long with base 0.5 mm oroad. Leaves ovate, up to 160 x 180 mm, base truncate or slightly cordate, lobation variable, usually doubly or dentately lobed to 'A width of leaf, with 3 or 4 pairs of major acute, triangular lobes, middle lobe up to 55 mm long, dark green when fresh, usually drying dull dark green, with simple pilose hairs on both surfaces of leaves, rarely with stellate hairs on underside, prickles on midrib and petiole slender, ± 15 mm long, base ± 2 mm broad, prickles on primary lateral veins slender, ± 7 mm long, purple near base, upper part yel low, the base 0.8 mm broad: petiole 4-80 mm long. Inflorescences simple. 3-5(6(-flowered: peduncles up to 0.5 mm long; pedicels ± 10 mm long. Calyx: lobes often unequal, elongating immediately after anthesis and con cealing immature fruits with subcaudate lobe tips, pubescent, becoming prickly in fruit. Corolla 10-15 x 25-30 mm, stellate, white, greenish or yellow-green, sometimes with a purple tint, rarely with purplish hairs. Stamens: filaments green to yellow; anthers Yellow. Style white; pistil pale green. Fruit nodding, globose, 15-30 mm diam., smooth, pale green with medium green stripes or white with green reticulation when young, dirty yellow or brownish when ripe. Seeds 2-4 mm diam., brownish, moderately flattened, seed coat closely investing endosperm, with margin sometimes thickened but not wing-like. Figure 1. Whalen (1984) gave the distribution of this species as southeastern Brazil (natural) and Central Africa (natural ized). Jaeger (1985) stated: 'the wide distribution of this species in Africa, and its scarcity or even absence from the New World, together suggest that S. aculeatissimum is native to Africa. This gives section Acanthophora an inex plicably disjunct distribution. However. S. aculeatissimum grows as a weed of secondary vegetation, indicating that it is more likely to be an introduction to Africa: and when it is considered that trade routes between the New World and Africa have been established for over 400 years (Roe 1979). an early introduction of this species would allow time for its subsequent dispersal. Its hideously spiny habit must deter grazing and contribute to its success.'  confirmed that S. aculeatissi mum seems to have been in Africa for a long time, hav ing achieved a very wide distribution in the Afromontane regions in western, eastern and southern Africa. Nee (1991) reported that S. aculeatissimum occurs naturally mainly from Rio Grande do Sul. Parana and Santa Catarina states in Brazil. He also reported that this species has long been grown in European botanical gar dens where it is very uniform and may represent a single introduction from South African populations, which they strongly resemble.

Distribution
Because of confusion with 5. capsicoides and other heavily armed species of Solanum. distribution records of S. aculeatissimum in the literature are often not reli able. In southern Africa, this species is fairly common in Limpopo [Northern Province]. Mpumalanga. KwaZulu-Natal. Eastern Cape and rare in the Free State. Lesotho and Western Cape, with one isolated record in the North-West almost on the border with Gauteng ( Figure 2). It is also so; .times cultivated as a curiosity in these areas, o ' in botanical gardens: Forbes NH34644 (NH) was grown at the Botanical Station. Durban in 1944.

Ecology
Nee (1991) recorded that 5. aculeatissimum is a weedy shrub that grows in disturbed or pastured forest, in grazing fields and along roadsides, from 400-1 200 m altitude, in sub-Saharan Africa it is found at forest edges and in savan nas. mostly in the eastern uplands of the great lakes region, but scattered through the rain forest and into South Africa, from 1 (M K >-2 400 m. rarely descending almost to sea level. ' Gbile (1979) described this as a highland species in Nigeria that grows mostly on rough ground and amongst rocks. According to Bukenya & Carasco (1995). S. aculea tissimum generally grows in forest clearings in Uganda: according to Bukenya & Hall (1988). it is a rare species in secondary forest in western Ghana.
In southern Africa. S. aculeatissimum grows in forest margins and clearings, along forest paths, and among undergrowth in closed natural forest, but also in Finns and Eucalyptus plantations. It prefers damp, shady places under shrubs and trees. It is also found along roadsides and in other disturbed areas, as a weed in gardens, ploughed fields as well as grassland. Wells et al. (1986) listed S. aculeatissimum as a ruderal, silvicultural and pastoral weed of the temperate and subtropical summer rainfall areas in southern Africa. It is found on gentle and steep mountain and hill slopes, in gorges and valleys, but also on flats; it can grow on moist humus-rich and red-brown loamy soil and also on well-drained sandy or stony soil. It is common in mountainous areas and is recorded from about sea level to ± 2 200 m altitude, with a rainfall of up to 2 000 mm annually. Acocks (1988) listed S. aculeatissi mum as one of the generally occurring smaller plants of the forest floor and margin in his Northeastern Mountain Sourveld which is one of the Inland Tropical Forest Types. He also listed it as one of the smaller plants of general occurrence in the Highland Sourveld which is one of the Temperate and Transitional Forest and Scrub Types. Nee (1991) stated that in Brazil, its natural distribu tion area, flowering is confined from October to February, similarly in East Africa, but throughout the year in the Democratic Republic of the Congo. In south- ern Africa it flowers from about November to March and fruits from about November to April.

Chromosome number and chemistry'
Both Fedorov (1969) and Bukenya-Ziraba (1996) list ed 2n = 24. Dalziel (1937) reported that the stem contains solanine, an alkaloidal glucoside with physiological action like saponin, but much less poisonous. Watt & Breyer-Brandwijk (1962) also reported that S. aculeatissimum contains solanine. The immature fruit is said to contain more solanine than the mature. Reports that the plant is toxic to cattle, horses and even humans are suspect as they may not be referring to the true S. aculeatissimum. Hepper (1978) stated that the steroidal alkaloid solasodine always occurs in the fruits of 5. aculeatissimum. but little is found in the leaves. Roddick (1986) gave figures for the amounts of solasodine in the leaves and fruit, con firming Hepper. Hutchings et al. (1996) reported that solasodine, solamargine and solasonine have been isolat ed from leaves, stems, fruit pericarps and seeds. The highest concentration of glycoalkaloids was found in seeds, followed by fruit pericarps, leaves and stems. Solasonine accounted for about 80# of the total glyco alkaloids, whereas solamargine accounted for about 13%, and was not found in stems. Mehra (1979) reported that in Malaysia the leaf juice of 5. aculeatissimum is used in a ritual preparation to be taken at childbirth. In Puerto Rico the sliced fruit of S. aculeatissimum (or plants known as) is fatal when con sumed by cockroaches (Mabberley 1997). In Liberia, the fluid prepared by boiling the fruits of S. aculeatissimum is applied in an enema for constipation (Dalziel 1937). Gbile & Adesina (1988) reported the same for Nigeria. In West Africa the fruit and the root are used as remedies for cough and dysmynorrhoea. Hutchings et al. (1996) reported that in Transkei. South Africa, the ripe fruit is applied to the forehead for headaches and is used for healing the navels of new-born babies, and smoke from burning plants is used for toothache (also in Nepal); root decoctions are taken for backache and impotence. An infusion of the root is a Zulu snake-bite remedy (Watt & Breyer-Brandwijk 1962). In Eastern Cape. South Africa, it was noted on the voucher, Bradley 49 (GRA). that the poisonous fruit is used for skin infections and the root for flatulence and as a purgative.

Medicinal and other uses
Mil ro scope studies Gbile & Sowunmi (1979) described the pollen of 5. aculeatissimum as subprolate and triangular, polar axis ± 28.0 pm, equatorial diameter ± 22.5 pm. with the sexine pattern faintly distinct. Nee (1986) investigated the placentation pattern of S. aculeatissimum. The placenta is H-shaped in cross section, allowing the seeds to till the total interior of the large fruit. At maturity the septum is a very thin film, resulting in a more or less unilocular berry. The 'ribs' running down the sides of the inner peri carp at the carpellary midvein strongly suggest traces of the false septum of 5. sisymbriifolium Lam., but does not indicate a close relationship. Gbile (1986) observed straight upper epidermal walls in the leaves of S. aculea tissimum. which is an uncommon occurrence in a meso morphic montane species. Groth (1989) studied the seeds of S. aculeatissimum: they are ellipsoid or subdiscoid with a finely punctate surface. The embryo is circinate and the cotyledons lanceolate. Ogundipe & Daramola (1997) also investigated the leaf epidermis: the anticlinal cell walls have a wavy pattern, the adaxial cells (± 38.0 x 15.5 pm) have an irregular and the abaxial cells (± 33 x 15 pm) an isodiametric cell shape: the abaxial stomata (± 28.5 x 17.0 pm) are anomocytic.
In southern Africa. 5. aculeatissimum can be distin guished from related species by its yellow ripe fruit, seeds without wings and by its stems with scattered sim ple hairs and acicular prickles.

Potential fo r crop improvement
Several investigators have looked at hybridization with S. melongena L. (aubergine, brinjal. eggplant). Rao (1979) reported successful crosses between S. melongena and S. aculeatissimum. Pearce & Lester (1979) showed that S. aculeatissimum has very little serological rela tionship with the taxa of the eggplant complex. Hybrids produced seed which did not germinate. Daunay. Lester & Laterrot (1991) recorded that S. aculeatissimum is resistant to Verticillium, but susceptible to Meloidogyne spp., which are both eggplant pests.

Notes
The specific epithet refers to the large number of sharp prickles. Numerous common names have been recorded e.g. Bailey & Bailey (1977): cockroach berry, love apple, soda apple nightshade; Wells et al. (1986): apple-of-Sodom and devil's apple for southern Africa; Jeffery RUH49I9 (GRA): Peru apple.
The photograph and description published by Rhind (1975) in a popular journal for South African farmers, belong to S. aculeatissimum and not to the indigenous S. panduriforme E.Mey.. as claimed in the discussion accompanying the photograph.

Distribution
The native range is 'coastal Brazil south of the Amazon' (Nee 1979). S. capsicoides is adventive on the Caribbean Islands, in Central and South America, also in the southern United States. It is a common weed in southern China and elsewhere in Asia; also in New South Wales and Queens land in Australia where it is called devil's apple.

Ecology
Solanum capsicoides is native to coastal Brazil near Rio de Janeiro and is apparently adapted to the restinga vegetation of the coastal sand dunes (Nee 1979). It prefers high rainfall, coastal lowlands of tropical and subtropical regions. It becomes a naturalized weed in disturbed sites, clearings, forest margins and other open habitats. It seems to have a wide ecological range and Morton (1976) claimed that S. capsicoides (S. ciliatum) is hardy as far north as Baltimore. Maryland in the USA. Man is probably responsible for its initial wide dissemi nation; it has been in European botanical gardens for more than two centuries.
For some unknown reason it has spread fairly slowly in Africa. In KwaZulu-Natal it was collected at ± 15 m altitude in shade at the edge of a forest in stony sand on a disturbed site. It seems to flower and fruit throughout the year.
The berries were reported to be poisonous to calves in Australia (Symon 1982) and Nee (1991) noted that the fruit is considered to be poisonous in northeastern Brazil. The fruit of S. capsicoides is used as a cockroach poison in parts of tropical America and this plant is sometimes called cockroach berry in the United States (D 'Arcy 1974). Its toxicity to humans is unknown. According to Daunay. Lester & Laterrot (1991), S. capsicoides is resis tant to Pseudomonas and is a non-host plant for potato cyst-nematodes. They also reported that S. capsicoides is graft-compatible with S. melongena. but is not used as a rootstock as it contains toxic alkaloids.

Taxonomy and diagnostic characters
This species has often been confused with the quite distinct S. aculeatissimum which has neither winged seeds nor vermillion fruit. It was also previously known under the synonym. S. ciliatum (Hepper 1979). Other synonyms are listed by Lebrun & Stork (1997) and Whalen (1984). Nee (1979) believed that this species, which has been known and grown for a long time and has been described several times under various names, might have an older name which could emerge from some obscure publication. He also noted that the slightly accrescent, stoutly prickly calyx of S. capsicoides might indicate a relationship with 5. sisymbriifolium Lam. of section Cryptocarpum Dunal.
Fourcade collected the type of his 5. macowanii at 700 ft (± 235 m) altitude in the forest near Storms River. Humansdorp Div., Eastern Cape, in April 1921. and quoted another specimen. MacOwan 1493. from the Somerset East Div.. also in Eastern Cape. He stated that S. macowanii was close to S. acutissimum Jacq. (sic) 'from which it differs by the branches and the lower surface of the leaves being glabrous, by the entire leaf lobes, and by the flowers being geminate.' Jaeger, Nee and Lester all identified the isotype of S. macow anii in K as S. capsicoides: PRE has a colour photo graph of this specimen. The specimen of MacOwan 1493 in GRA has a much more spiny stem than the type and one unripe fruit with immature seeds. Apparently S. capsicoides has not been collected again in Eastern Cape since 1921 and it could have died out in that area. Ross (1972) quoted Ward 4888 as 5. aculeatissimum Jacq. in his checklist ot the Flora o f Natal, but this specimen has orange-red ripe fruit and winged seeds and is clearly S. capsicoides.
The large orange-red fruit with winged seeds and the absence of stellate hairs make 5. capsicoides unique in the southern African context.

Notes
S. capsicoides is occasionally cultivated for its orna mental vermillion dry fruits which keep their colour for a long time. |The large-fruited form common in cultiva tion is var. macrocarpum Hort. (Morton 1976).] This species could have a 'shaker' mechanism for seed dis persal (Nee 1991). The ripe dry fruit splits irregularly into 2-A lobes and releases the dry winged seeds, which adhere neither to each other nor to the pericarp. The inner fruit wall of the unilocular ovary is ± 4 mm thick, slight ly juicy and spongy; it is nearly tasteless and dries to a virtually invisible thin film soon after the fruit begins to split. The conspicuous fruit colour could indicate a very recent derivation from ancestors with bird-dispersed seeds. Nee (1986) noted that the placentas are split into two 'horns' and at maturity are attached only to the base of the fruit. The fruit and seed dispersal method of 5. capsicoides probably is an adaptation to its natural sandy habitat; the placentation ensures space for a great num ber of large seeds. The evolutionary significance of the winged seed is not clear (Nee 1979). It could perhaps aid in local dispersal by wind or water.
The species name refers to the resemblance of the fruit to that of the solanaceous genus Capsicum.

Distribution and ecology
Solanum mammosum is native to the Caribbean (Nee 1979), but has spread by long distance dispersal, direct migration or with the casual or deliberate assistance of humans to the tropical lowlands of South and Meso-America. It is now often naturalized in disturbed, lowland habitats in the tropical and subtropical regions of both hemi spheres. though not yet in Africa (Jaeger 1985) or Australia (Symon 1981). Nee (1991) stated that S. mammosum now occurs mostly from sea level to 1 (X) m altitude in tropical America, but can occur as high as 1 800 m. It flowers and fruits throughout the year with no special season. It can be expected to become naturalized or to escape locally from cultivation in areas of high rainfall, whether this is seasonal or year-round. It has been known as a curiosity in botanical gardens for several centuries and is occasionally cultivated as an ornamental in tropical Africa; also in southern Africa in frost-free or frost-protected localities.

Chromosome number and chemistry
Heiser (1971) gave references of reports for both n = 12 and n = 11; the latter was the first report of n = 11 in the genus Solanum. Dan & Dan (1984) recorded the occurrence of nuatigenin and iso-nuatigenin (two rare isomeric non-nitrogenous sapogenins) as the main root constituent of S. mammosum and some other species of Solanum. Roddick (1986) listed 1 °Ic of solasodine (dry weight) in the fruit of S. mammosum. while Mabberley (1997) referred to the molluscicidal glycoalkaloids of the fruit. Nee (1991) stated that the immature fruits contain the highest concentration of glycoalkaloids and that other plant parts contain varying amounts or none.

Medicinal and other uses, potential for crop improvement
Solanum mammosum (macaw bush, nipple fruit, pig's ears) is widely cultivated in tropical and warm temperate regions for its unique ornamental but also poisonous fruit. In the Americas, these fruits are w idely used for killing rats and cockroaches, also for catching fish, extracting maggots and curing common colds (Nee 1979). Heiser (1971) quot ed the use of the leaves as a narcotic in Bolivia. Daunay, Lester & Laterrot (1991) listed that 5. mammosum is resis tant to Fusarium wilt and several other pests and diseases of 5. melongena cultivars. They also regarded it as frost resistant, but susceptible to Meloidogyne incognita and Verticillium, both pests of S. melongena.

Microscope studies
The glandular villous pubescence in this species is composed of reduced stellate hairs in which the rays are fused w ith the leaf lamina and the mid-point remains as an apparently simple hair (D 'Arcy 1974). The structure of this hair type is best observed in seedlings. Similar hairs occur in S. capsicoides (= S. ciliatum), but they are not so dense and are less commonly glandular. Whalen & Costich (1986) listed a report on female sterility of short-styled flowers in S. mammosum, and noted that embryo sac development in these flowers was abnormal.
Taxonomy and diagnostic characters Whalen (1984) and Lebrun & Stork (1997) listed a number of synonyms for this species. Wright (1904) expressed doubt whether the S. mammosum Thunb. in his revision of the South African species of Solanum, is the same as S. mammosum L. The description does not men tion the unique fruit. A specimen (Thunberg s.n.) collect ed in the Swellendam Div. (Western Cape) in the late 18th century is quoted; probably before S. mammosum L. was introduced into South Africa. However, no specimen of it was found in Thunberg's herbarium in 1883.
Solanum mammosum has a pubescent calyx without prickles, a showy pale blue to violet corolla, yellow. ripe mammiform fruit and seeds at least 5 mm wide, lacking marginal wings. In southern Africa, S. mam mosum has so far only been recorded in a cultivated state, and not yet as naturalized or even as a garden escape.

Notes on the fruit
Miller (1969) made a thorough study of the morphol ogy and development of the unusual mammiform fruit of S. mammosum. Wild specimens in the Western Hemis phere show considerable variation in fruit shape, from entirely globose to mammiform with an apical nipple and five protuberances at the base. The more unusual forms were probably selected by man from a teratological abnormality and used as an ornamental and for its extremely poisonous fruit. There has apparently also been a selection for plants less prickly than the wild form (Nee 1991). Nee (1986) studied placentation patterns in the Solanaceae. The basic fruit in Solanum is 2-locular with a slightly enlarged placental area in the centre of the sep tum, from which the seeds radiate into the usually pulpfilled locules between the septum and the pericarp. In the mature fruit of S. mammosum, the septum can hardly be seen, and is only a thin film, easily destroyed; the pla centas are connected only at the base. Nee (1979) sug gested that the spongy mesocarp may adapt the fruit to dispersal by water flotation.

Distribution
Originally from southern Brazil, Paraguay, Uruguay and northern Argentina, but S. viarum has spread to other areas of South America, also Central America, the West Indies and the southern United States (tropical soda apple). It was introduced into India and Nepal and also into Africa; it is recorded in the Democratic Republic of the Congo and possibly also in Cameroon (Jaeger 1985). Probably accidentally and sporadically introduced into Africa and can be expected to spread to many other sub tropical areas (Nee 1991).
In southern Africa, specimens have been collected in Swaziland, KwaZulu-Natal and Eastern Cape (Figure 4). The earliest record seen for this study, was collected in 1962: Marr & Harding 54 (PRE) from the Natal Agri cultural Institute. Pietermaritzburg. KwaZulu-Natal.
Ecology Wunderlin et al. (1993) reported that in Florida S. viarum is usually found in soils belonging to the order of Spodosols, that means nearly level, somewhat poorly drained soils with a spodic horizon 1-2 m below ground level. In South Africa it has been collected on welldrained. reddish brown, sandy loam soil, with a western, northwestern or eastern slope, from 30-800 m in alti tude; elsewhere it is reported from low altitudes, mostly below 100 m. S. viarum prefers full sunlight, but will also grow in the shade.
It is often a common weed of natural areas, improved pastures, croplands, roadsides and fence rows, waste places, open disturbed sites, secondary growth and forest edges. In southern Africa it was also collected in open woodland and pine plantations. In more tropical areas, flowering and fruiting occurs throughout much of the year (Nee 1991), but in southern Africa flowering and fruiting material has been collected from November to April, with one fruiting specimen in August.

Weedy characters, dispersal and control
Solanum viarum can produce up to 50 mature fruits per plant, each fruit containing numerous seeds. Accord ing to Bryson & Byrd (1994), it has been on the Florida noxious weed list since 1994. It was present in that state since about 1980 and spread very rapidly and aggres sively, being able to form near monocultures in certain situations, although its opportunistic adaptations may restrict it to disturbed areas.
Its foliage is generally not grazed by cattle, probably because it is heavily armed with prickles and glandular hairs, although they will sometimes eat the bitter mature fruit. It can be transported from pasture to pasture in con taminated hay and farm machinery. The primary means of dispersal seems to be livestock and wildlife, including birds. Scarification of seeds by digestive systems ot ani mals seems to promote seed germination. Movement of livestock that have recently ted on S. viarum fruit will has ten its spread. Bryson & Byrd (1994) found that in mature plants the root systems were up to 300 mm deep and lat eral roots up to 1 m long. They also found that experi mentally detached green fruit more than 20 mm in diame ter will ripen in sunlight. Seed germination from these fruits was more than 70%. Fruit from less than 10 mm in diameter up to mature yellow or dry fruit are extremely buoyant and can then also be dispersed by water. Control of this plant therefore requires elimination of immature and mature fruit as well as the whole plant including the root system. Fedorov (1969) gives 2n = 24 as the chromosome num ber for S. khasianum.

Chromosome number, chemistry, medicinal use and poten tial fo r crop improvement
The section Acanthophora contains several species with a high alkaloid content (Nee 1991). Of these S. viarum is the species most studied, as it contains a high percentage of sola sodine. concentrated in the berries. Dan & Dan (1984) listed S. viarum as a high solasodine yielding plant (the alkaloid of pharmaceutical interest). Roddick (1986) listed 0.7-3.0% of solasodine (dry weight) in the fruit. It is a common weed in India since at least 1932 where it is also grown as a com mercial source of this glycoalkaloid which is a key interme diate in the synthesis of steroid drugs (Maiti et al. 1979). Saini (1966) found that the 'fleshy cover' and washed seeds of S. khasianum var. cluitterjeeanum do not contain any alkaloid: most is found in the mucilaginous layer around the seeds. When fruits are dried, the mucilaginous layer dries to a white powder which is easily lost or is capable of contam inating the seed or pericarp assay. This provides an explana tion for the discrepancies in the literature of the glycoalka loid content from different parts of the fruit. Daunay. Lester & Laterrot (1991) reported that S. viarum is resistant to the following diseases of S. melongena: Leucinodes orbonalis, Epilachna vigintioctopunctata, Phomopsis blight, 'little leaf and partially resistant to Meloidogyne incognita. It is also a non-host plant for potato cyst-nematodes. Morton (1976) regarded S. viarum as a synonym of 5. reflexion Schrank. However. S. reflexum is a synonym of S. aculeatissimum. a different but closely related species, see above (Nee 1991). Lester (1978) pointed out that the descrip tion given by Morton for S. reflexum. is that of S. viarum. Lester (1978) also pointed out that careful examination showed that S. khasianum var. cluitterjeeanum (which is commonly, but incorrectly called simply S. khasianum) is S. viarum. More synonyms arc listed by Lebrun & Stork ( 1997).

Taxonomy and diagnostic characters
A good character for distinguishing S. viarum from all other species of section Acanthophora is the presence of glandular hairs on the ovary in young flowers.
In the past, specimens in South African herbaria have often been misidentified as S. aculeatissimum, but the combination of long straight prickles on the leaves and petioles and short curved prickles on the stems distin guishes S. viarum from all other members of Solanum in southern Africa. The density of the prickles, however, is an unreliable taxonomic character, particularly in domes ticated species of Solanum subgenus Leptostemonum.

Notes
The species name probably refers to the habitat as described on the type specimen: 'Ad vias et circa domos vulgare in provincia Brasiliana S. Pauli' (Dunal 1852).
Large shrubs or small trees. 2-10 m high; early growth prickly on both stems and leaves; later growth usually unarmed or only sparsely prickly or bristly; sympodial units difoliate, commonly with geminate leaves; cauline pubescence of stalked or sessile stellae. varying in densi ty, often with reduced midpoints: cauline prickles, when present, usually straight, subulate or broad-based, lateral ly compressed. Leaves petiolate. large and repand on early growth: later leaves medium to large, ovate to broadly ovate, 30-140 x 70-300 mm. entire, repand or lobed. usually unarmed, stellate-pubescent on both sur faces, with stalked stellae below, pubescence of upper surface very variable in structure and diagnostic of spe cies. Inflorescences cory mbose or cymose. lateral or ter minal and becoming lateral by continued shoot growth, usually unarmed, remote from leaves, asymmetrically several-to many-branched. rarely simple, inflorescence branches monochasial. bearing female-sterile flowers with reduced gvnoecia distally; peduncles short or well developed: pedicels unarmed, slender and flexuous in flower. Calyx variable, from nearly truncate to attenuatelobed. Corolla white or lavender, stellate-pentagonal or less commonly deeply stelliform w ith narrow, nearly sep arate lobes. Stamens with anthers equal, slender and tapering. Fruit: berries small to medium. 5-15 mm diam., glabrous. 4-locular: pericarp tough and leathery, green, dull yellow or brown when ripe: flesh saponaceous and sticky. Chromosome number: n = 12. rarely 24. 36. Whalen (1984) included some 50 species in his S. torxum group, occurring from Mexico to southeastern Brazil, with many endemics, mostly in South America. He believed that there may also be several species indigenous to southeastern Asia and the East Indies. Two species are widely introduced in the Old World tropics. Solanum torxum Sw.. originally from Mexico, Central America and the West Indies, is now a common intro duced w eed throughout the tropics of both hemispheres, but it has not been listed before for southern Africa (Welman 1993). 5. chrysotriclium Schltdl. (= S. hispidum auctt. non Pers.) originally from Mexico to Panama, is now widely introduced in the Palaeotropics. In the past, this species was often misidentified as S. hispidum Pers.. but true S. hispidum Pers. is restricted to the Andes of southern Colombia. Ecuador and Peru.

Ecology
According to Whalen (1984). the habitat preferences of section Torva are variable, ranging from sea level to over 3 000 m altitude, often in forest edges, grazed fields, and other places where direct sunlight is available. Most of the species show weedy tendencies. These large shrubs or trees are characteristic of secondary vegetation and grazed lands throughout the montane Neotropics. Species grow in understoreys and edges of montane and seasonal forest, in dry tropical woodland, in savanna, and even in subalpine elfinwoods. Bitter (1921) placed the Afro-Asian plants (series Giganteiformia Bitter) under the Neotropical section Torxaria Bitter (section Torxa Nees). Whalen (1984) and Jaeger (1985) claimed that section Torxa is cladistically not closely related to the Afro-Asian species, the former separating the Giganteum group, the latter keeping them together for convenience. Jaeger (1985) emphasized the particular differences between the neotropical Torxa (lobate leaves, bifoliate geminate sympodial units, white flowers and firmer, larger, green to yellow fruits) and the African endemic species of the series Giganteiformia Bitter, raised to sectional level as Giganteiformia (Bitter) Child in 1998. Species of that section have plurifoliate sympodia, inflorescences with shortened, umbelloid branches, and succulent, red, translucent berries. Nee (1991) suggested that sec tion Acanthophora may have been derived from the large section Torxa.

Taxonomy
Morphology and reproductive biology Child (1979) noted that section Torxa has many-flow ered corymbose cymes where most flowers are hermaph rodite and fully fertile. Nee (1979) recorded that it is com mon in section Torx'a for the flowering branches to lack prickles, whereas the lower stem or young shoots are quite prickly. Whalen & Costich (1986) stated that section Torx a is weakly andromonoecious, short-styled flowers are pre sent, fruit size is small and the species are self-compatible. Child & Lester (1991) gave the following summary of sec tion Torxa: trifoliate sympodial units with anisophyllous geminate leaf clusters, inflorescences subsessile to pedun culate, generally lateral, leaf remote to subopposed, pleioto monochasial, pleiochasia with most flowers hermaphro dite. fully fertile, but fewer-flowered inflorescences with often only proximal flower(s) hermaphrodite, distal flowers brachystylous, functionally male, some taxa androdioecious; mostly shrubs to trees, some climbers.

Potential fo r crop improvement
Daunay, Lester & Laterrot (1991) noted that sterile hybrids have been obtained by artificial crosses between S. melongena and species of section Torxa.

Distribution
Solanum chrysotrichum is native to tropical Central America from southern Mexico to Costa Rica and Panama. It had been introduced widely in the Old World tropics as an ornamental plant, and has now been naturalized in many areas, such as in disturbed sites in the Brisbane area of Queensland (Australia) where it is known as giant devil's fig (Symon 1982). It has been collected in West Africa (e.g. Nigeria), Zimbabwe and Malawi and also in southern Africa.
In southern Africa, S. chrysotrichum seems to be natu ralized only in Eastern Cape from about the Albany to the Libode Districts ( Figure 6). The oldest record seen in this study dates from 19()9. collected near Grahamstown (Mally A7788, GRA). It is sometimes cultivated in gardens in that province or persists as a garden relic, e.g. Jacot Guillarmod 4567 (GRA): Burns. Olyott & Potts 11 (GRA).

Ecology
In its native area. S. chrysotrichum is found in moist or wet thicket, sometimes in oak or oak-pine forests or in fields at 1 200-2 500 m in altitude (Gentry & Standley 1974). In South Africa it grows at an altitude of ± 250 m, in full sun and scattered along roadsides and in other dis turbed areas. It is also occasional on riverbanks and near water courses, in hillside scrub and valley vegetation where it can be found with Zantedeschia, Senecio ilicifolius and aliens like Acacia longifolius, A. melanoxylon and Melia azedarach. Wells et al. (1986) described S. chrysotrichum as a summer rainfall ruderal and flora weed, which does not seem to spread aggressively. In South Africa, it appears to flower almost throughout the year, while fruiting is from October to June. Roe (1971) described the stem hairs of S. chryso trichum from Mexico as multiseriate-stalked. porrectstellate with rather short central rays. Gbile & Sowunmi (1979) described the pollen of 5. chrysotrichum as oblatespheroidal with a triangular amb and indistinct sexine pattern. The polar axis is ± 21.6 pm and the equatorial diameter is ± 22.0 pm. Fedorov (1969) reported the chromosome number n = 12 for S. chrysotrichum (as S. hispidum). Dan & Dan (1984) reported that the fruits and leaves of S. chrysotrichum contain non-nitrogenous spirostane sapogenins and are devoid of any alkaloid. The major leaf constituents are the spirostane sapogenins neochlorogenin and paniculogenin. The chemical consti tuents of the roots of S. chrysotrichum are not known.

Uses and potential fo r crop improvement
No reports of any medicinal use of S. chrysotrichum were found in the literature. It is a garden subject in the warmer parts of the world. Khan (1979) reported that S. chrysotrichum had been crossed with the economically important S. melongena L. and produced fertile hybrids. Daunay. Lester & Laterrot (1991) reported that S. chry sotrichum is resistant to Pseudomonas. Meloidogyne and Verticillium. and partially resistant to Thielaviopsis. all of which attack S. melongena. It is also a non-host plant for potato-cyst nematodes.

Taxonomy
Most literature references to S. hispidum refer to S. chrysotrichum. True 5. hispidum Pers. is from the Andes; the upper surface of the leaves is hairless or almost so (Shaw 2000). D' Arcy (1973) reported that S. chryso trichum can hybridize with S. ton um in nature, at least in Panama.

Diagnostic characters and derivation o f species name
Solanum chrysotrichum differs from all other species of Solanum in southern Africa by its coarse, reddish brow n pubescence, particularly on the calyx, stems, young parts and main veins on the underside of the leaves. The species name refers to the indumentum of golden (reddish brown) hairs.

Distribution and ecology
Solanum torvum is native to the West Indies and Meso-America, but is now a common weed throughout the humid tropics. It grows in forest areas of west, east and central tropical Africa, also in Madagascar; in south ern Africa it is found in the districts of Mtunzini. Lower Tugela. Inanda and Durban in KwaZulu-Natal ( Figure  6). The oldest record seen in this study dates from 1932: Galpin 11868 (PRE) was collected on the Lower Tugela River bank, Stanger. This species was cultivated in a gar den in Stellenbosch in 1937 [Herre NBG162978 (NBG)]. In the early 1950s the Durban Botanical Station cultivat ed S. torvum from seed received from Buitenzorg, Java in 1949 [Wager NH64099, 64100 (NH)].
In its native area, 5. torvum is a very common weedy shrub ot the lowlands and grows in dry or wet thickets, often in secondary growth, just above sea level to 1 500 m. Elsewhere it can be an aggressive weedy species in humid areas, generally at low altitudes where it becomes common in disturbed sites such as old gardens, pastures, roadsides and other waste places, also near human habi tation. It thrives well on good soils and grows quickly in abandoned clearings and becomes common in exploited forest reserves. It is well established along the tropical coastline of eastern Queensland (Australia) where it is regarded as a noxious weed (devil's fig) and suspected of poisoning stock (Symon 1982).
Solanum torvum is a successful colonizer because of its weedy and opportunistic characters: it fruits plentiful ly and produces large numbers of seeds per fruit. The seeds germinate quickly in sunlit conditions, showing that dormancy is controlled by shade (Hall & Swaine 1980). Husaini & Iwo (1990) noted that in Nigeria, S. torvum grows in damp places, in soil with a pH of 6.1 such as ferrasols, ferruginous tropical soils and lithosols.
In southern Africa S. torvum grows from about sea level to 200 m, often on red clayey sand, along river and stream banks, in swamp forest, open shrubland, coastal thorny bush and secondary scrub, often in clearings and other disturbed places. It does not seem to be an aggres sive weed in this area. In KwaZulu-Natal flowering and fruiting material have been collected from April to Oc tober. Ahmad (1964) noted that the stomata on the lower leaf surface are 27 x 22 pm in size. The epidermal cell walls on the lower leaf surface are sinuous, whereas those on the upper surface are slightly sinuous. Ogundipe & Daramola (1997) found that the stomata are narrowly elliptical in surface view outline; stomata are present on both leaf surfaces. They also found that the abaxial and adaxial cells are both irregular in shape. The abaxial anti clinal cell walls are wavy while the adaxial anticlinal cell walls are wavy-sinuous. The outer periclinal walls are flat. The abaxial and adaxial cells are both ± 38 x 19pm in size. Ahmad (1964) noted that the hairs on both the upper and lower leaf surfaces are of two types: firstly unicel lular and dagger-shaped and secondly stellate with an elongated many-celled. multi-seriate stalk bearing 4-9 rays. Bukenya & Hall (1988) found that the young leaves have dense, stalked, stellate hairs on both sur faces; mature leaves have more or less sessile, stellate hairs on the upper surface, 4-6-armed with one arm much longer than the rest, whereas the lower surface has stalked, stellate hairs of 8 or 9 more or less equal arms. Gbile & Sowunmi (1979) described the pollen of S. torxum as subprolate with a circular amb and distinct sexine pattern. The polar axis is ± 25.9 pm and the equa torial diameter is ± 21.2 pm. Fedorov (1969) and Daunay. Lester & Laterrot (1991) reported a chromosome number of n = 12. Randell & Symon (1976) reported n = 24; this was confirmed by Husaini & Iwo (1990).

Chromosome number and chemistry
The roots and leaves of this species yield steroid alka loids of the 3-aminospirostane group (Schreiber 1979). Dan & Dan (1984) reported that the major leaf constituents of S. torvum are the spirostane sapogenins neochlorogenin and paniculogenin. The leaves, fruits and roots contain non-alkaloidal as well as alkaloidal sapogenins. The roots contain jurubidine which is a 3-amino-spirosolane alka loid. Jaeger (1985) noted that the steroidal alkaloids solasodine and jurubidine as well as the sapogenins chlorogenin and neochlorogenin/paniculogenin had been record ed for 5. torvum. Mabberley (1997) listed this species as one of the commercial sources of solasodine. Jain & Borthakur (1986) noted that in India the ripe fruits of S. torvum are eaten as a vegetable. Bukenya & Hall (1988) reported that the fruits are collected in some parts of Ghana and used in soup and stew. D' Arcy & Rakotozafy (1994) reported that this species is cultivated in countries like India and Myanmar for its fruits which are used as seasoning. Mabberley (1997) noted that in Sri Lanka the fruits are used in curry after the toxic seeds have been removed. Jain & Borthakur (1986) recorded that in India 5. torvum alone or in combination with other medicinal plants, is used for chest pain (fruits), snake bite and insect stings (leaves), stomach pain (fruits and roots), antidote to poisoning (roots), malaria (bark), night blind ness (fruits), tooth infections (fruits). Lu (1986) recorded that in China the roots of this species, containing juru bidine, jurustune and other compounds, are used to "dis perse extravasated blood,' relieve pain and alleviate coughs. Gbile & Adesina (1988) noted that the ripe fruits are used for liver and spleen complaints; the fruits are expectorant and sedative. Roddick (1991) listed 5. torvum as an antidote for various poisons, toothache, snake and insect bites and as an ingredient in malarial preparations in India and as a cough medicine and gen eral pain killer in China.

Potential for crop improvement
Solatium torvum is graft-compatible with S. melongena and is resistant to Pseudomonas, Meloidogyne, Verticillium, Thielaviopsis, Phytophthora parasitica and the Pliytophtliora and Fusarium solani complex. It is resistant to Epilachna vigintioctopunctata and to little leaf disease, but highly susceptible to Colletotrichum gloeosporioides. It is a non-host plant for potato cystnematodes (Daunay et al. 1991). In Cuba S. laciniatum Aiton. which is cultivated as an important source of the alkaloid solasodine, has been grafted onto S. tonum (Esquivel & Hammer 1991). Gooding (1965) rejected the name 5. ton um Sw. as an illegitimate and superfluous substitute by Swartz for S. indicum L. and replaced it with the later name S. ficifolium Ortega. However. Heine (1976) and Hepper (1978) pointed out that Swartz realized that Linnaeus had included both Old and New World elements under his S. indicum references. Swartz then grouped the West Indian element under S. tonum . which is a legitimate name, with his own material as type.

Taxonomy
Solanum ton um has become naturalized widely and as a result, numerous synonyms have been recorded (Bitter 1921;Gentry & Standley 1974;Symon 1981;Lebrun & Stork 1997). Only synonyms based on African types are listed in the present article. The fact that the leaves of this species present a great range of leaf size and lobing, depending on age and vigour, also caused several superfluous varieties to be described. In Central America it seems to hybridize with several other similar species (D 'Arcy 1974); this makes the taxonomy of the section complicated. Wright (1904) listed S. ferrugineum for the Durban area in KwaZulu-Natal, but described the fruit as black; Bitter (1921) believed that he was not dealing with the true S. ferrugineum. The specimens quoted were not seen in this study. Wright (1906) listed 5. ferrugineum as a synonym of S. ton um. but Bitter (1921) disagreed with that, as he regarded these two species as related but dif ferent. D' Arcy (1973) also regarded S. ferrugineum as a synonym of 5. ton um, but Nee (2001) viewed them as two distinct species.

Notes on stylar heteromorphism
Hossain (1973) studied stylar heteromorphism in 5. ton um. the term used when two forms of flower are noticeable in each inflorescence, a character seen in sev eral species of Solanum. In one form, the style is long and distinctly exserted; in the other, it is short and includ ed w ithin the conically connivent anthers, so that it is not visible from outside in an open flower. Hossain noted that in S. tonum the later-formed distal flowers have slightly reduced ovaries and much shortened styles, and so act as male flowers, forming a small proportion of the inflorescence. Only the lower flowers in any inflores cence are structurally hermaphrodite which explains the characteristic incomplete fruit set in this species.

Diagnostic characters and derivation o f species name
In southern Africa 5. tonum can be recognized by its rough, hairy leaves and its manv-flowered inflorescences w ith fairly large white flowers and numerous large yel lowish berries, drying black. Sterile specimens can be confused with S. anguivi Lam., but 5. ton um has dense, fairly short-rayed stellate hairs on both sides of the leaf, whereas S. anguivi has fewer stellate hairs each with a single long ray or midpoint. Symon (1985) stated that since the specific epithet means savage, gloomy, grim and fierce, it could refer to the drab aspect of the plant or the stout prickles on the stems.