Solanum viarum [Dunal ]

Solanum viarum

Citation author:

Dunal

Citation:

Prodr. [A.P de Candolle] 13(1): 240. 1852.

Type:

Brazil, São Paulo, P. Lund 799 (Holotype: G DC [F photo 6816, IDC microfiche 800-61.2080:I.1]).

Last edited by:

Sandra Knapp (May 2014)

Written by:

Michael Nee, Maria S. Vorontsova and Sandra Knapp

Habit:

Shrubs 0.5–2 m tall, erect but with many spreading branches, armed. Young stems terete, densely and uniformly glandular-puberulent with simple, uniseriate, gland-tipped trichomes 0.4–0.5 mm long, sparsely to moderately prickly with broad-based recurved prickles, variable in length and the largest to 8 mm long, the base puberulent with a mixture of minute, gland-tipped trichomes and longer acute simple trichomes ca. 0.2 mm long, the smaller prickles ca. 1 mm long, slender, straight and spreading.

Sympodial structure:

Sympodial units difoliate, usually geminate.

Leaves:

Leaves simple, the blades 7–10 (–15) cm long, 6-8 (–15) cm wide, about as long as wide, usually geminate, with one about twice the size of the other, ovate to suborbicular, membranous, sparsely prickly adaxially and abaxially with straight spreading acicular prickles similar to those of the largest petiole prickles, grading down to minute prickles on smaller veins; adaxial surface densely puberulent with 2-3-celled simple hyaline trichomes 0.4–1 mm long, at least the shorter ones gland-tipped; abaxial surface densely puberulent with simple gland-tipped hairs ca. 0.4 mm long and with longer simple hyaline hairs up to 0.8 mm long, mixed with sessile stellate trichomes, the rays 4 (–5), 0.4-0.5 mm long, the midpoints 0.5–0.8 mm long; base cordate to truncate; margins lobed, usually with 3-5 pairs of shallow obtuse or acute lobes, these entire or again with small secondary lobes or teeth; apex acute or obtuse; petioles of the major leaves 3–6 cm, with pubescence similar to that of the stem but also with a few scattered simple 3-celled hyaline hairs to 1.2 mm long, with 3–10 straight acicular spreading prickles 5–18 mm long, longer than those of the stem.

Inflorescences:

Inflorescences lateral, sessile or nearly so, unbranched, with 3–5 flowers, densely pubescent with simple gland-tipped hairs 0.4–0.6 mm long, with some longer simple hyaline hairs up to 1.2 mm long, unarmed or with a few straight spreading prickles up to 2 mm long; peduncle 0-0.3 cm; pedicels 0.7-1.1 cm long, tightly congested on the minute axis.

Flowers:

Flowers 5-merous, heterostylous, usually only the lowermost (rarely 2) flowers long-styled and fertile, the rest short-styled and staminate. Calyx 2-4 mm long, with pubescence similar to that of the pedicel but often with more copious simple hyaline trichomes up to 1.2 mm long, unarmed or with a few prickles to 2 mm long, the lobes 0.8–2 mm long, 0.6–0.8 mm wide, triangular, acute at the tips. Corolla ca. 2 cm in diameter, pale greenish white or white, stellate, lobed nearly to the base, the lobes 7–10 mm long, 2.5–3 mm wide, narrowly lanceolate, acute at apices, very often recurved in herbarium specimens, pubescent abaxially with simple gland-tipped hairs to 0.6 mm long, glabrous adaxially. Stamens equal, connivent, the filament tube minute, the free portion of the filaments 1–1.8 mm long, glabrous; anthers 5.5–6.9 mm long, 1–1.5 mm wide, tapering, free, light yellow to cream, poricidal at the tips, the pores small and directed distally. Ovary conical, densely puberulent with simple uniseriate trichomes 0.2–0.35 mm long mixed with minute shorter gland-tipped simple trichomes, these all deciduous by the time the ovary expands to ca. 5 mm in diameter after anthesis; style of long-styled flowers 6.8–8.2 mm long, straight, glabrous; stigma capitate, minutely papillate.

Fruits:

Fruit a globose berry, 1-2(-3) per infructescence, 2.2–2.5 cm in diameter, light green mottled with dark green when immature, yellow at maturity, glabrous at maturity, with a whitish or greenish layer of spongy mesocarp; fruiting pedicels 1-2.1 cm long, ca. 2 mm thick and scarcely enlarged at the apex, terete, curved around the inflorescence axis; fruiting calyx somewhat accrescent, the lobes 4–6.5 mm long, 3.2–4 mm wide at base.

Seeds:

Seeds 100-300 per berry, 2.2–2.8 mm long, 2–2.5 mm wide, flattened-reniform, light red-brown.

Chromosome number:

2n=24 (Nee 1979).

Distribution:

Paraguay, northeastern Argentina and Uruguay through much of eastern Brazil; sporadically present in Africa, long naturalized on the Indian subcontinent (Babu 1971), and recently becoming a noxious weed in cattle pastures in the southeastern United States (Wunderlin et al. 1993); often a common weed of campo, pastures, roadsides, waste places, cultivated ground, second growth and edges of forest at low elevations, mostly below 1000 m.

Phenology:

Flowering concentrated from September through April, but flowering throughout much of the year.

Phylogeny:

Solanum viarum is one of three very closely related species of subgen. Leptostemonum sect. Acanthophora (Nee, 1979, 1999). A key to sect. Acanthophora is provided by Nee (1991). This series is a well-supported monophyletic group that also includes S. myriacanthum Mexico and northern Central America and S. aculeatissiumum Jacq. of Brazil, Africa and the Indian subcontinent (Babu, 1971; Nee, 1979; Levin et al., 2005; Stern et al. 2011). Within Leptostemonum (Bohs, 2005), the Acanthophora clade is a monophyletic group that includes most of the species traditionally recognized in Solanum section Acanthophora Dunal (the S. mammosum species group of Whalen, 1984; Levin et al., 2006; Stern et al. 2011).

Commentary:

Solanum viarum is most easily distinguished by the initially dense puberulence of the ovary. The hairs are often difficult to see but usually persist until the expanding fruit is about 5 mm in diameter, when they are scattered over the surface. Care must be taken not to mistake these for miscellaneous loose hairs which often become stuck to the young fruits of this and related species. The largely sympatric S. palinacanthum is the only other species of sect. Acanthophora to have a puberulent (as opposed to minutely stipitate-glandular) ovary, but this perennial species is easily distinguished by its larger purple flowers and large fruits and seeds.

Solanum viarum is similar to S. myriacanthum and S. aculeatissimum and the three species form a closely related complex (Nee, 1979, 1999). Solanum myriacanthum, however, is a Central American species and is not sympatric with S. viarum and S. aculeatissimum. Solanum viarum and S. aculeatissimum are sympatric in Brazil, but with only a few exceptions, do not appear to intergrade (Nee, 1979). In Africa Solanum viarum can be difficult to distinguish from S. aculeatissimum, the more common of the two species in Africa; S. viarum has deltate, versus long-triangular calyx lobes, a puberulent (rather than stipitate-glandular) ovary, and more uniform, fine glandular pubescence on the stems and new growth. The stem prickles of S. viarum are often somewhat curved and all the same size, while those of S. aculeatissimum are straight and of varying lengths.

Solanum viarum and S. aculeatissimum are the two most common introduced species in the Old World. It is interesting that S. aculeatissimum is common in Africa, while S. viarum is more common in Asia; it has become widely naturalized in south China and throughout India, where both species were previously known as S. khasianum (see Babu & Hepper 1979 for an account of the confusion in this group, their misinterpretations were corrected by Nee 1979). We have seen more specimens of S. viarum from West Africa (and a few from coastal South Africa), but it may be that the range of this species is increasing in Africa. Care in identifying specimens as S. aculeatissimum and S. viarum will be needed in order to track the spread of the latter. Solanum viarum was introduced to the southern United States in the late 20th century and is becoming a noxious weed there (Mullahey et al. 1998) due to its short juvenile period and its spread by livestock.

References:

Babu, C.R. 1971. The identity of Solanum khasianum Cl. var. chatterjeeanum Sen Gupta (Solanaceae). Journal of the Bombay Natural History Society 67: 609–611.

Babu, C. R. and F. N. Hepper. 1979. Taxonomy and nomenclature of Solanum khasianum and some of its relatives. Kew Bull. 34: 407-411.

Bohs, L. 2005. Major clades in Solanum based on ndhF sequences. Pp. 27-49 in R. C. Keating, V. C. Hollowell, & T. B. Croat (eds.), A festschrift for William G. D’Arcy: the legacy of a taxonomist. Monographs in Systematic Botany from the Missouri Botanical Garden, Vol. 104. Missouri Botanical Garden Press, St. Louis.

Mullahey, J. J., D. G. Schilling, P. Mislevy, and R. A. Arkanda. 1998. Invasion of Tropical Soda Apple into the U.S.: lessons learned. Weed Technol. 12: 733-736.

Nee, M. 1979. A revision of Solanum section Acanthophora. Ph.D. thesis, University of Wisconsin, Madison, Wisconsin, USA.

Nee, M. 1991. Synopsis of Solanum section Acanthophora: a group of interest for glycoalkaloids. Pp. 257–266 In: J.G. Hawkes, R.N. Lester, M. Nee, and N. Estrada-R. (eds.). Solanaceae III: Taxonomy, Chemistry, Evolution. Richmond, Surrey, UK: Royal Botanic Gardens, Kew and Linnean Society of London.

Nee, M. 1999. Synopsis of Solanum in the New World.

Pp. 285–333 in M. Nee, D. E. Symon, R. N. Lester & J. P. Jessop (eds.), Solanaceae IV: Advances in Biology and Utilization. Royal Botanic Gardens, Kew.

Levin, R.A., K. Watson & L. Bohs 2005. A four-gene study of evolutionary relationships in Solanum section Acanthophora. Amer. J. Bot. 92(4): 603–612.

Levin, R.A., N.R. Myers, & L. Bohs 2006. Phylogenetic relationships among the "spiny" solanums (Solanum subgenus Leptostemonum). Amer. J. Bot. 93: 157-169.

Stern, S. R., M. de F. Agra, and L. Bohs. 2011. Molecular delimitation of clades within New World species of the ”spiny solanums” (Solanum subgenus Leptostemonum). Taxon 60: 1429-1441.

Whalen, M.D. 1984. Conspectus of species groups in Solanum subgenus Leptostemonum. Gentes Herbarum 12 (4): 179-282.

Wunderlin, R.P., B.F. Hansen, K.R. Delaney, M. Nee & J.J. Mullahey 1993. Solanum viarum and S. tampicense (Solanaceae): two weedy species new to Florida and the United States. Sida 15: 605–611.

Conservation status:

Least Concern(LC); an invasive weed, often noxious.

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