Flora of North America species comparison

Solanum triflorum is found in South America (Argentina) and is also considered to be native to central and western North America. It is occasionally adventive in the eastern United States. It is poisonous to livestock and can become a serious weed in cultivated fields, especially in the Great Plains.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Species ca. 1500 (52 in the flora).

Solanum is the largest genus in the Solanaceae and one of the largest genera of angiosperms. It is the most speciose genus in the family in North America. The North American taxa are composed of natives, most of which have ranges that extend into Mexico or the Caribbean, and a number of species that have been introduced deliberately or unintentionally. Some of these have spread and become naturalized, occasionally as pests, whereas others are only sporadically or ephemerally escaped from cultivation.

Solanum is one of the world’s most economically important genera. It includes crop plants such as the potato, tomato, and eggplant as well as species used on a small scale as edible fruits or as ornamentals. Most Solanum plants contain high levels of alkaloids and can be toxic. In general, the foliage or unripe fruits of Solanum species should not be consumed by humans or other animals due to danger of poisoning.

Sclerotic granules (also called stone cells) occur in fruits of some Solanum species. These are hardened masses within the fruit pulp that are usually spherical, 0.5–5 mm in diameter, and visible with 10× magnification. In dissected fruits they are generally paler, rounded, and more homogeneous in appearance than the seeds. The number of sclerotic granules per fruit can be diagnostic in species of the black nightshade group. They are very numerous in S. laciniatum and S. triflorum and can be seen in pressed fruits without dissection.

Some Solanum species are cultivated as foods or ornamentals and may occasionally escape, while other non-native species are known only from historical records.

The potato (Solanum tuberosum Linnaeus) is the world’s leading root crop and second only to the cereal grains in food production. Potatoes are widely cultivated in agricultural fields and home gardens. Volunteer plants of potato can grow from discarded tubers but do not appear to persist or spread. Eggplants (S. melongena Linnaeus) are commonly grown in home gardens or as specialty vegetables in small-scale agriculture. They may occasionally escape from cultivation in southern Florida but have not become naturalized. Solanum retroflexum Dunal (sunberry, wonderberry) and S. scabrum Miller (garden huckleberry) are sometimes grown for their edible fruits but apparently do not escape from cultivation. Solanum glaucophyllum Desfontaines is known in the United States only from two specimens collected in Pensacola, Florida, over a hundred years ago. Solanum pilcomayense Morong, native to Argentina and Paraguay, is only known from two collections made in port areas in New Jersey and Texas, but it has also not been collected since the early 20th century and is not established. Solanum villosum Miller (hairy nightshade, woolly nightshade) is an occasional introduction from the Old World but has not persisted or become naturalized in North America. It was first recorded in the United States in 1899 in Pensacola, Florida, perhaps arriving in ships’ ballast. After this manuscript was completed, S. houstonii Martyn (syn. S. tridynamum Dunal) was discovered in Santa Cruz County, Arizona. This species was formerly considered endemic to Mexico (S. Knapp et al. 2017). It is most similar to S. hindsianum but differs in its dimorphic hermaphroditic and staminate flowers with strongly unequal anthers in the latter.

The North American Solanum flora includes a number of species in the black nightshade group (Solanum sect. Solanum, or the Morelloid clade). These can form hybrid and polyploid complexes and are notoriously difficult to identify. Previous floras have used erroneous names or conflated several species under a single name, often referring to all black nightshades in an area as S. americanum or S. nigrum. Many of the older determinations of specimens in herbaria should be considered suspect. The North American black nightshade species comprise natives and endemics (for example, S. emulans, S. interius, S. pseudogracile) as well as introduced or adventive species from Central and South America and the Old World. This is still a difficult group under active study. T. Särkinen et al. (2018) includes complete descriptions, nomenclature, and synonymy for taxa treated here that have been introduced from the Old World. S. Knapp et al. (2019) similarly treated the black nightshade species of North and Central America and the Caribbean.

(Discussion copyrighted by Flora of North America; reprinted with permission.)