Solanum laxum (Knapp, Sandra 2013)
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Ordo: Solanales
Familia: Solanaceae
Genus: Solanum
Name
Solanum laxum Spreng., Syst. Veg. 1: 682. 1824 – Wikispecies link – Pensoft Profile
- Solanum laxum Knapp, Sandra, 2013, PhytoKeys 22: 1-1.
Description
Description. Woody vine, the base sometimes to> 10 cm in diameter, twining by petioles. Stems strongly zig-zag, glabrous or puberulent when young with white simple uniseriate trichomes <0.5 mm long; new growth glabrous to minutely and sparsely puberulent. Bark of older stems green or reddish green or often purplish green when growing in bright sunlight. Sympodial units plurifoliate. Leaves simple or very occasionally deeply pinnatifid with 1-4 irregular lobes, 1-5 cm long, 0.5-2 cm wide, ovate or elliptic to narrowly elliptic (occasionally pinnatifid with up to 5 lobes), widest in the basal 1/3, membranous to chartaceous, the upper surfaces glabrous or with a few simple uniseriate trichomes along the midrib, the lower surfaces glabrous or with variously dense tufts of simple uniseriate trichomes to 1 mm long in the vein axils and occasionally extending sparsely to the lamina; primary veins 4-6 pairs, with a strong and obvious intramarginal vein, the midrib often keeled; base truncate, often oblique and asymmetrical; margins entire, if lobed the lobes reaching nearly to the midrib, the basal ones smaller; apex acute to acuminate; petioles 0.4-2.5(+) cm long, glabrous or minutely puberulent in the groove on the adaxial surface, twining. Inflorescences terminal, or later lateral, to 5 or more cm long, to many times branched, but usually only 2-3 times branched, with up to 50 flowers, glabrous; peduncle 0.5-4 cm long, very variable in length depending on the size and age of the inflorescence; pedicels 1-1.5 cm long, <0.5 mm in diameter at the base and apex, filiform, nodding or spreading at anthesis, glabrous, articulated at the base from a small sleeve, leaving a small peg on the inflorescence axis; pedicel scars irregularly spaced 2-6 mm apart. Buds somewhat inflated, ellipsoid, broadest in basal part, the corolla strongly exserted from the calyx before anthesis. Flowers all perfect, 5-merous. Calyx tube 1-1.5 mm long, conical to somewhat flattened, the lobes 1-1.5 mm long, deltate with an elongate tip to 1 mm, often drying black, glabrous or the tip with a few minute trichomes. Corolla 1.8-2.2 cm in diameter, white or pale violet, rotate-stellate, lobed ca. 1/2 way to the base, the lobes 7-9 mm long, 5-6 mm wide, planar or spreading at anthesis, glabrous to minutely pubescent with tiny simple uniseriate trichomes abaxially, these <0.2 mm long, glabrous adaxially. Filament tube minute, the free portion of the filaments 1-1.5 mm long, glabrous or minutely puberulent within; anthers 3.5-4 mm long, 1-1.5 mm wide, ellipsoid, loosely connivent, sagittate at the base, poricidal at the tips, the pores lengthening to slits with age. Ovary glabrous; style 7-8 mm long, pubescent with simple uniseriate trichomes <0.2 mm long within the anther tube, glabrous where exserted beyond the anthers; stigma a minutely papillate area on the tip of the style, occasionally somewhat bilobed to clavate. Fruit a globose berry, ca. 1 cm in diameter, blackish purple when ripe, the pericarp thin and shiny, glabrous; fruiting pedicels 1.2-1.5 cm long, ca. 0.5 mm in diameter, not markedly woody, pendent. Seeds 10-20 per berry, ca. 3 mm long, ca. 2.5 mm wide, flattened reniform, pale tan, the surfaces minutely pitted, the testal cells pentagonal. Chromosome number: n=12 (Moscone 1992, as Solanum boerhaviifolium).
Distribution
Distribution (Figure 55). Native to southeastern Brazil from the states of Minas Gerais to Rio Grande do Sul to the mouth of the Rio de la Plata in Argentina and Uruguay, and into Paraguay, from nearly sea level to above 500 m elevation. Widely cultivated worldwide in both temperate and subtropical zones, often escaped and naturalised.
Discussion
Discussion. Solanum laxum was long known in cultivation as Solanum jasminoides (see Figure 56), but the former name has priority and is slowly becoming accepted in botanical (see Mentz and Oliveira 2004) and horticultural circles (see Royal Horticultural Society (RHS) Plant Finder, http://apps.rhs.org.uk/rhsplantfinder/index.asp). The original source of material cultivated in Great Britain was southern Brazil, and in England the plant overwinters well even in very cold winters (hardy to USDA zone 8), where it dies back from frost, but quickly resprouts. In cultivation vines of Solanum laxum grow very large; a vine growing up the south-facing wall of the Chelsea Physic Garden in London is over 10 cm in diameter at the base. Solanum laxum is similar, and probably closely related, to the sympatric Solanum viscosissimum with which it shares rotate-stellate corollas, pubescent styles and purplish black berries. It differs from that species in its almost always simple leaves and in the tufts of trichomes in the vein axils of the leaf undersurfaces; Solanum viscosissimum usually has at least some deeply pinnatifid leaves and has long, glandular trichomes evenly spread over the leaf surfaces. Flowers of Solanum laxum are usually white, but can have a purplish tinge, especially when growing in strong light. Solanum laxum could also potentially be confused with Solanum flaccidum, also sympatric, which differs in its larger purple or violet flowers with anthers borne on unequal filaments and in its more evenly distributed pubescence on leaf surfaces and stems. A few collections (e.g., Stuckert 11592, G) have deeply pinnatifid leaves, but can be distinguished from other similar species such as Solanum seaforthianum (also common in cultivation) by the conspicuous tufts of trichomes in the vein axils on the leaf undersides. These pinnatifid leaves are probably juvenile, and are very occasionally found on stems mixed with simple leaves (e.g., Osten 8265) as is common in other species of the Dulcamaroid clade. Although the tufts of trichomes in the vein axils of the leaf undersides are a good diagnostic character for Solanum laxum, some populations and individuals appear to lack pubescence of any sort. These plants have been called var. calvum, and they differ from other populations only in pubescence density; there are usually a few trichomes, but they can be difficult to see without a microscope. This variation is common in the Dulcamaroid clade, and in many other non-spiny solanums. The Sellow collection used by Sprengel to describe Solanum laxum was destroyed in Berlin; I have found no Sellow collections of Solanum laxum from Uruguay. Many of Sellow's collections were sent to Berlin, and plants were grown there from seeds sent from Uruguay in 1823 (Krausch 2002). The plant used by Sprengel may have been one grown in the Botanic Garden in Berlin rather than a herbarium specimen collected in Uruguay. I have selected as a lectotype for Solanum laxum a specimen (BM000935924, the only one I have seen in several hundred collections examined) collected in Montevideo, Uruguay attributed to James Anderson, the botanist aboard HMS Adventure. The ship, captained by Philip Parker King, surveyed the complex area around the Straits of Magellan from 1826 to 1830, but little information as to the orgins of the plants from the voyage exists (see entry for King on JSTOR Plants, http://plants.jstor.org/person/bm000063285). This specimen, although a unicate and not collected by Sellow, is almost contemporary with Sellow's time in Uruguay and matches in the protologue in having glabrous leaves. An un-numbered Sellow collection from Brazil at B ("Brasilia australi"was used by Sendtner (1846) in describing Solanum boerhavifolium; this is probably no longer extant. Another Sellow specimen at P (P00324767) donated by Berlin, and annotated "S. borhaaviaefolium Sendt." in Sendtner's hand, is selected as the lectotype. It bears a number "250" in a different handwriting. Another Sellow sheet from B at P (P00324768) is sterile and does not have the specific name written in Sendtner's handwriting, but may be a duplicate; a sheet at K (K000590026, also with the species name in Sendtner's hand, but labelled on the sheet "Klotsch") is probably also be a duplicate, but in the absence of specific locality information or collection number it is impossible to tell. The origin of the plants described as Solanum jasminoides is discussed by Harley (1970), who speculates that the plants grown in the Young Nursery in Epsom, Surrey, were originally from Sir William Hooker, who received material from Brazil collected by Tweedie. A specimen at Kew collected in 1832 in Rio Grande do Sul (K000545751, labelled "Parana") by Tweedie is thought by Harley (1970) to probably be the origin of both the Kew and the Epsom material; Tweedie collected both specimens and seeds for Hooker. I am not sufficiently convinced of this chain of custody to use the K sheet as epitype material. The epithet boerhaviifolium was spelled "boerhaviaefolium" by Sendtner (1846) and although the name honours Hermann Boerhaave, the original spelling with a single 'a' is retained, following Article 60.1 of the Code (McNeill et al. 2012).
Taxon Treatment
- Knapp, Sandra; 2013: A revision of the Dulcamaroid Clade of Solanum L. (Solanaceae), PhytoKeys 22: 1-1. doi
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