Solanum diphyllum aka Twoleaf Nightshade

Solanum diphyllum has two common names: two-leaf and twin-leaf nightshade. This small shrub lives for years. It belongs to Solanaceae, the potato family. Its native range runs from Mexico to Pacific Costa Rica. It grows in dry lowlands within this range. Gardeners have grown it for its leaves, flowers, and orange fruit. It has spread from gardens in tropical and subtropical regions.

Plants reach about 3–6 feet [0.9–1.8 metres] tall. Useful Tropical Plants gives a range a little wider than this. Its upper end reaches 6.6 feet [2 metres]. The shrub has no spines. Its smooth stems spread out from the plant. Older wood has clear lenticels, or pores in the bark. Stems with fruit bend at their nodes, making a slight zigzag. Shade gives the plant dark green leaves and a loose, straggling shape. Full sun gives it paler leaves and a denser crown. Plants can form small thickets in Florida.

Each leaf is simple, with one blade. The leaves feel smooth and have no hairs or breaks along their edges. Shoots without fruit bear leaves in an alternate pattern, one after another. These leaves narrow at the base and widen toward the tip. Shoots with fruit bear two unequal leaves at each node. The larger leaf is longer and more oval. The smaller leaf has a rounder blade and almost no stalk. A few nodes bear three leaves of different sizes.

Flowers appear from late spring into early fall. Young plants start to bloom near 2 feet [0.6 metres] tall. They start to branch at about the same stage. The small flowers grow in coiled groups called helicoid cymes. Their five petals curve back as the flowers open. White flowers turn toward pale lavender as they age. Insects pollinate them. The plant is self-fertile: its own pollen can set seed. Flowers and berries can share the same stem. Hard green berries grow fleshy and bright orange as they ripen.

This shrub grows in warm climates, including some warm temperate areas. UF/IFAS reports that it tolerates cold down to 30°F, around USDA zone 9a. Frost may kill shoots, but roots can send up new growth. Growers can raise plants from seeds and half-ripe cuttings. Useful Tropical Plants reports that ripe fruit is edible. Its safety warning covers nightshades as a group. It does not confirm that this species is toxic. Birds spread the seeds, which can survive buried for two years. Florida listed it as a Category II invasive plant in 2017. UF/IFAS urges caution throughout the state. It also advises keeping the plant from escaping gardens.