Endemic to Chile [Regions I (Tarapacá), II (Antofagasta), III (Atacama), IV (Coquimbo), V (Valparaíso), VI (Liberador), VIII (Bío-Bío), Metropolitana. On dry, sandy or rocky coastal slopes and dunes, 3–2300 m in elevation.
This species belongs to the Regmandra clade of Bohs (2005), an isolated clade within the non-spiny solanums.
Solanum pinnatum is a morphologically variable species from Chile. The leaf shape and indumentum are particularly variable, ranging from small, narrowly dissected leaves with the pinnae almost needle-like (such as those of the type of S. maritimum) to much larger and more rounded lobes such as those of the type of S. novemlobum. An examination of a large number of specimens has shown that leaf size and shape are continuously varying characters and cannot be divided into discrete taxa. Consequently, a large number of previously described species are here placed in synonymy.
The species can be recognised by the singly lobed leaves and usually dense inflorescences. The calyx and filaments are shorter than those of another Chilean species with lobed leaves, S. paposanum. Solanum paposanum also differs by its densely velutinous indumentum and narrowly acute apices to the leaf lobes. The fruits of S. pinnatum are unusual among species of section Regmandra because they contain a very small number of seeds; the majority of the fruit contents consists of stone cells. The low seed set (< 5 seeds per fruit) is particularly intriguing given how widespread this species is, particularly around Coquimbo and Valparaíso, in Chile.
Bohs, L. 2005. Major clades in Solanum based on ndhF sequences.
Pp. 27-49 in R. C. Keating, V. C. Hollowell, & T. B. Croat (eds.), A festschrift for William G. D’Arcy: the legacy of a taxonomist. Monographs in Systematic Botany from the Missouri Botanical Garden, Vol. 104. Missouri Botanical Garden Press, St. Louis.