Mexico to Pacific Costa Rica in drier lowland areas from 0 to 250 m. Escaped from cultivation in many tropical and subtropical areas: e.g; Florida, Java, and the Antilles.
Solanum diphyllum is a member of the Solanum pseudocapsicum group of the Geminata clade (Knapp, 2002; Bohs, 2005).
Solanum diphyllum is most similar to S. malacothrix, a rare species from western Mexico. The two species share small flowers with reflexed petals at anthesis and berries borne on erect pedicels. Solanum diphyllum differs from S. malacothrix in its glabrous foliage. The mature fruit of S. malacothrix is not known (see discussion under that species).
Solanum diphyllum is native to Mexico and Central America, where it is widespread in drier habitats. It has been widely cultivated as a foliage shrub, and for its pretty flowers and brightly colored fruits, in tropical and subtropical areas where it is hardy such as Italy, southern France, and Florida (D'Arcy, 1974), the Antilles, Java, and the Philippines, and has escaped in some of these areas.
Solanum diphyllum is an attractive shrub, with its tiny white-purple flowers and bright orange fruits. It is self-compatible, but not autogamous. All the flowers are long-styled and the plants set abundant fruit when exposed to pollinators. In cultivation the plants are bushy, with many leaves. In their native Mexico however, shrubs of S. diphyllum are often quite straggly (Nee, pers. comm.).
In Mexico and Central America Solanum diphyllum is remarkably uniform morphologically and is usually easily recognizable. A single geographical variant occurs in Pacific coastal Chiapas. In the municipalities of Arriaga and Cintalapa, near the Mar Muerto on the Pacific coast and somewhat inland, plants of a narrow-leaved race of S. diphyllum are common. Plants from this area have leaves that average 1 cm wide, but otherwise they conform to the other characters of S. diphyllum. Naming this minor variant would obscure its relationship to the rest of the species range.
The type specimen of Solanum diphyllum in LINN is annotated on the back "Solanum lignosum affic. sempervirens, cassinaefoliis. Br." in Linnaeus's handwriting (Savage, 1945). This is perhaps what led D'Arcy (1974) to speculate that the sheet was collected by Patrick Browne, as Linnaeus denoted specimens he received from Browne with a Br. On these sheets however, the specific names were written by Solander (Jackson, 1912). The type comes from the Clifford herbarium (Knapp & Jarvis, 1991; Savage, 1945). The printed vase at the base of the specimen is a characteristic mark of the sheets from that herbarium. Solanum diphyllum was included in the Hortus Cliffortianus (Linnaeus, 1737) as "5. Solanum caule inerme perenni, foliis ovato-lanceolatis geminis, altero minimo." The provenance of the plant was cited as either America or Africa, but Linnaeus emphasized America, so it is clear he thought (correctly) that the plant was from America. Solanum diphyllum was probably cultivated in Clifford's garden, the seeds are easy to grow and even in Ithaca, New York (Bailey Hortorium garden) and London grow to reproductive maturity in one summer.
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