Solanaceae, the Nightshade Family
Tropical soda apple (also known as TSA) is a shrubby, herbaceous perennial plant that grows 3 to 6 feet high. The sturdy stems are finely pubescent with simple hairs and bear broad-based, recurved prickles (and occasionally straight prickles). The alternate leaves are borne on petioles up to 2 inches long. The leaf blades, which are ovoid in shape with three to five broad lobes on each side, measure 4 to 8 inches long and 2 to 6 inches wide. Leaf surfaces are covered with a mix of simple, gland-tipped and stellate (star-shaped) hairs. These three types of hairs are barely discernible with a 10X hand lens and are more easily observed with a microscope. The glandular hairs often give the leaves a glistening appearance and make them slightly sticky to the touch. Straight, rigid, yellowish prickles are scattered along the midvein and secondary veins on both the upper and lower leaf surfaces, as well as the petiole. The inflorescence is an extra-axillary (located between or beside the axils) raceme of one to five flowers. The five-lobed, campanulate (bell-shaped) calyx is hairy and often prickly. The white flowers, which measure about ½ inch across, have five narrow, recurved petal lobes. The prominent pale yellow- to cream-colored anthers are connivent (converging, but not actually fused). The fruit are globose berries ½ to 1½ inches across. Immature fruit are pale green with darker green markings. At maturity, they turn dull yellow and have a slightly sweet fragrance. Each leathery-skinned berry contains up to 400 seeds, which are small, round and lenticular (or biconvex: curving or bulging outward on both sides). The seeds are covered in a mucilaginous layer that contains the potentially toxic glycoalkaloid solasodine. In Florida, flowers and fruit may be produced throughout the year, but are most common from September through May.
Native to southern Brazil, northeastern Argentina and neighboring parts of Paraguay and Uruguay, tropical soda apple is now naturalized in the West Indies, Mexico and Central America, as well as tropical regions of Africa, Asia and Australia. It has invaded most of the southeastern and south central United States, from North Carolina and Tennessee west to Texas and Oklahoma. Isolated records indicate that it seems to have been introduced, but has not become established, in Pennsylvania and California.
First reported from Florida in 1988, tropical soda apple has now been vouchered with herbarium specimens from most counties in the peninsula and several in the eastern Panhandle. It is particularly problematic in disturbed sites such as pastures, citrus groves, vegetable fields and roadsides, but has also been observed in a variety of natural habitats including scrub, flatwoods, swamps, floodplain forests and on the edges of pinelands and hammocks.
In Florida, there are at least seven other species of nightshade (Solanum spp.) with petiolate leaves and prickles present on mature plants. Tropical soda apple is the only one with leaves bearing a mix of stellate, simple and gland-tipped hairs.
New plants may develop from its extensive root system, but seed is the primary dispersal mechanism for this species. A single plant is capable of producing as many as 50,000 seeds in a single year. Livestock, deer, feral pigs, raccoons and possibly birds consume the fruit and disperse the seeds of tropical soda apple. Seeds are also spread in contaminated soil, sod and hay and by construction and agricultural equipment.
Tropical soda apple is a fast-growing, rapidly spreading species that adapts to a broad range of environmental conditions. It displaces native plant species and poses a serious threat to the cattle and vegetable industries. Agricultural impacts include reduced production capacity and accessibility in pastures, groves and vegetable fields. This species is a host for a number of viruses that affect important solanaceous crops, including pepper, tomato, eggplant, potato and tobacco. It was added to the Florida noxious weed list in 1994 and the federal noxious weed list in 1995.
A successful biocontrol program involving the tropical soda apple leaf-eating beetle, Gratiana boliviana, has provided considerable control of the TSA weed by causing extensive defoliation. The beetle, which attacks and damages TSA exclusively, was first released on a Polk County, Florida, ranch in 2003. Since then, beetles have been released in Florida, Georgia, Alabama and Texas, spreading from one to 10 miles per year from the initial release sites.