Naranjilla or Lulo (Solanum quitoense) is a sub-shrubby perennial with orange fruits slightly larger than a golf ball. The greenish flesh yields a juice with a flavor that has been described as a blend of orange, pineapple, and tomato. The plant is around 2 m tall with purplish stem and leaves. Two varieties of this species have been recognized, quitoense, a spineless form found in southern Colombia and Ecuador, and septentrionale, a form with spines found in central Colombia, Panama, and Costa Rica that is also grown in French Polynesia. Naranjillo is cultivated widely within its range, but also has characteristics of a "weed" and is often considered a species in the process of being domesticated.
Solanum is an enormous genus that includes many well known plants of agricultural importance (e.g., Potato, Tomato, Eggplant). Within the Solanum subgenus Leptostemonum, Naranjilla belongs to the section Lasiocarpa, a clade that includes around 13 species of perennial shrubs or small trees with a center of distribution in northwestern South America. Several species in this section produce edible fruits and two of them, Naranjilla and Cocona (S. sessiliflorum), are economically important fruit crops in Latin America. Naranjilla has been introduced to Panama, Costa Rica, and Guatemala and is now naturalized in Central America and cultivated in French Polynesia (where there is some concern it could become an invasive weed).
Naranjillo has often been identified as having potential for development as a premium crop for international markets, but some practical hurdles must be overcome, notably the production of varieties with better pathogen resistance. Wild relatives of Naranjilla are a source of desirable traits that could be exploited for genetic improvement. For example, crosses of Naranjilla with S. hirtum have reportedly yielded varieties with the same taste as Naranjilla, but with resistance to root knot nematodes.
(Heiser 1985; Bohs 2004; Bedoya-Reina and Barrero 2010 and references therein)