Solanum sessile
On the eastern slope of the Andes from Colombia to Bolivia, extending into Amazonian Brazil. A species of wide altitudinal range, from 100 m in the Amazon basin to 1800 m on the slopes of the Andes in central Peru and Venezuela.
Solanum sessile is a member of the Solanum sessile sepcies group of the Geminata clade (Bohs, 2005).
Knapp, S. 1991. A cladistic analysis of the Solanum sessile species group (section Geminata pro parte: Solanaceae).
J. Linn. Soc., Bot. 106: 73-89.
Knapp, S. 2002. Solanum section Geminata (G. Don) Walpers (Solanaceae).
Flora Neotropica 84: 1-405.
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.
With the exception of Solanum oppositifolium, S. sessile is the most widespread and variable of the species of this group. It is most closely related (Knapp, 1991b) to S. obovalifolium (Cordillera de la Costa, Venezuela) and S. monadelphum (E Andean slope, Peru). Solanum sessile differs from the former in its much more complexly branched inflorescences, larger, fleshier flowers, and large, obovate, usually sessile leaves. It differs from S. monadelphum in its larger leaves, inflorescences, and flowers. Solanum sessile rarely grows in the riverbed habitat of S. monadelphum. In the forests of Quincemil (Dept. Cuzco, Peru), intermediates between S. sessile and S. monadelphum occur (see discussion of S. monadelphum). The most distinctive features of S. sessile are its large, branched inflorescences, and large, fleshy flowers.
Solanum sessile is a widespread species, with several well marked geographical races. These are briefly described here.
1) Populations from near Muña, in middle elevation central Peru, have strongly sessile leaves, congested inflorescences with little or no axis between the flowers, and very large, fleshy flowers. Ruiz and Pavón's collection of Solanum sessile is from this area, an isolated Andean valley in the department of Huánuco.
2) In areas of central Peru (not including the above area near Muña), plants are quite similar in appearance to the preceeding form, but the inflorescences are open and many times branched, with somewhat smaller flowers. Most collections from middle to high elevation Peru are of this form.
3) More northern, lower elevation populations in Peru, Ecuador, Colombia, and Venezuela consist of plants with sessile leaves, the two leaves of the geminate pair markedly differing from one another, elongate, branched inflorescences, and pubescent berries. These populations have been called Pheliandra herthae and Solanum grandifolium.
4) Low elevation Brazilian populations with open branched inflorescences and glabrous berries are of two types, a) those with sessile leaves have been called Solanum marmellosanum, and b) those with petiolate leaves have been called S. pulchrum.
5) Plants from southeastern Peru and adjacent Brazil are almost completely glabrous, have sessile, geminate leaves, and glabrous berries. These populations grade into and are perhaps hybridizing with Solanum monadelphum.
6) Plants from high elevation Venezuela have coriaceous, sessile leaves that are often somewhat auriculate, and large open inflorescences.
Many other forms of even more local occurrence could be described. To give formal names to the elements of this complex mosaic of variation would be counterproductive, and would only serve to confuse an already confusing situation. The above well marked forms grade into one another, and the collection sample is quite small for this forest species. Although perhaps difficult for the field botanist, it is more realistic phylogenetically to leave this complex pattern under the name of Solanum sessile until detailed work is done on the complex.
Individuals of Solanum sessile are most likely andromonoecious, as they bear both long- and short-styled flowers. Few berries are set on any given inflorescence, lending support to this hypothesis. The sympodial structure of S. sessile is quite variable (see above and description), some plants have difoliate, geminate sympodia, while others appear to have plurifoliate sympodia (for discussion of sympodial types, see Knapp, 2002). This difference largely depends on the part of the plant taken to make the specimen in question. If only the most recent inflorescence is taken, the sympodia appear plurifoliate, and the inflorescence terminal, with no shoot growth continuing. On the other hand, if a lower node is taken, the inflorescence appears to be opposite the leaf, and the sympodium difoliate and geminate. Solanum sessile is a good example of the difficulties involved in using inflorescence position to identify species in section Geminata. This single species has been placed in two subgenera due to this variability.