Solanum viarum aka Tropical Soda Apple

Solanum viarum is known as tropical soda apple or Sodom apple. It belongs to the nightshade family, Solanaceae. Its native range spans southern tropical South America to northern Argentina. This includes Brazil and Argentina. Kew records it as an annual or shrub. NC State describes it as a perennial shrub. It now grows beyond its native range in the United States.

Plants reach 3–6 feet [0.91–1.83 metres] tall and wide. They grow fast and form dense stands with many upright stems. Young stems are green, hairy, and round in cross-section. They turn brown with age and bear long, straight prickles. The plant sheds its leaves. Its large, simple leaves grow in opposite pairs. Each blade has broad lobes and wavy edges. Dense hairs cover both faces, with prickles along the veins. The upper face is dark green; the lower face is paler. These leaves give the shrub a coarse look.

Small white flowers grow in clusters through most of the year. Each cup-shaped bloom has five petals. Round fruits start green, with pale mottled patches. They turn bright yellow as they ripen. Fruit can reach 0.125 feet [0.038 metres] across. Each fruit may hold as many as 400 seeds. One plant can bear up to 200 fruits each year. Fruit production peaks from September through May. Cattle eat the fruit and help spread its seeds.

This plant grows in full sun. Its native climate has a dry season within the tropics. It has little cold tolerance but can regrow after winter kills its stems. The evidence gives no precise hardiness zone or watering needs. It occurs in pastures, crop fields, and other disturbed ground. It also invades wooded sites, where dense growth can displace native plants. NC State lists southern bacterial wilt among its disease problems.

Its invasive spread is the main concern for gardens and farms. The United States lists it as a Federal Noxious Weed. North Carolina also lists it as invasive. Its dense, prickly growth can block access and harm farm and forest habitats. The fruit contains solasodine and poses a poisoning risk. Eating large amounts may cause stomach upset and loss of appetite. NC State rates the poison risk as low. It also flags the plant as a problem for dogs. The source reports no contact dermatitis.