Dunal
Description
Solanum viarum, the tropical soda apple, is native to subtropical South America, notably Brazil, Argentina, Paraguay and Uruguay, but is now a widespread invasive weed; the GBIF dataset of roughly 32000 records spans the United States, Australia, South Africa, India, China, Vietnam, Thailand, Korea, Mexico and the Himalayan countries Nepal and Bhutan. It colonises pastures, roadsides, field margins, waste ground and disturbed forest edges at low to mid elevations, thriving in open, grazed and ruderal habitats. The illustrated material from Zhemgang in Bhutan at 910 m in October and Taplejung in eastern Nepal at 1000 m in April reflects its establishment in the warm subtropical foothills, where it behaves as an aggressive colonist of disturbed ground.
It is a robust erect prickly perennial herb or subshrub 1–2 m tall, the stems, petioles, leaf veins and calyx armed with stout, broad-based yellowish prickles and clothed in stellate hairs. The leaves are alternate, ovate, deeply lobed and sinuate, prickly on both surfaces along the veins. The inflorescence is a small extra-axillary cyme of white, stellate, five-merous flowers with reflexed petals and a cone of connivent yellow anthers. The fruit is a globose berry about 2–3 cm across, mottled green like a tiny melon when immature and ripening pale yellow, containing numerous flattened seeds embedded in juicy pulp.
Solanum viarum belongs to the spiny Leptostemonum clade of Solanum. Its prolific, animal-dispersed berries, toxic to many vertebrates but readily spread by livestock and wildlife, underlie its notoriety as a noxious weed subject to quarantine and biological control in the United States and elsewhere. In the Himalayan foothills it is a naturalised invader rather than a native element, and its spread is monitored as a threat to pasture and native vegetation.
Author: Dunal · Sources: POWO (Kew), GBIF, Flora of China Vol. 17, Flora of Bhutan Vol. 2, Flora of Nepal, Solanaceae: A Monograph of Solanum (Solanaceae Source)