Solanaceae
Nightshade Family
Order: Solanales
Phylogenetic Position: Asterid clade
Family Overview
The Solanaceae, commonly known as the nightshade family, is a diverse and economically important family of flowering plants that includes approximately 2,700 species in about 98 genera. This family has a worldwide distribution but is most diverse in Central and South America, with Australia as a secondary center of diversity.
Members of this family range from annual and perennial herbs to vines, lianas, epiphytes, shrubs, and small trees. They are characterized by their alternate leaves, often showy flowers with fused petals, and fruit types that include berries and capsules. The Solanaceae includes some of the world's most economically important food crops, including potatoes, tomatoes, eggplants, and peppers, as well as tobacco, numerous ornamental plants, and several plants used in traditional and modern medicine.
The family is also known for its rich diversity of alkaloids, with many species containing compounds that are pharmacologically active in humans, ranging from therapeutic to toxic. This chemical diversity has made the Solanaceae both valuable and sometimes dangerous to humans throughout history.
Botanical Characteristics
Growth Form
Highly diverse, including annual and perennial herbs, shrubs, trees, vines, and epiphytes. Growth habits range from prostrate to erect, with heights from a few centimeters to several meters. Many species have a distinctive odor when the foliage is crushed.
Leaves
Leaves are typically simple and alternate, though sometimes appearing opposite near the inflorescences due to sympodial growth. Leaf shapes vary widely from entire to deeply lobed or compound. Leaves are often hairy or glandular, and many species have a characteristic odor when crushed. Stipules are absent.
Stems
Stems are typically herbaceous in annual species and woody in perennial species and shrubs. Many species have distinctive trichomes (hairs) or glands on the stems. Some species have modified stems such as tubers (e.g., potato) or rhizomes.
Flowers
Flowers are usually radially symmetric (actinomorphic), though sometimes bilaterally symmetric (zygomorphic) as in some Schizanthus species. They are typically bisexual and hypogynous (with superior ovary). The calyx typically has 5 fused sepals, often persistent and sometimes enlarging in fruit. The corolla usually has 5 fused petals, forming shapes ranging from rotate (wheel-shaped) to tubular, funnel-shaped, or salverform. Stamens typically number 5 (rarely 4 or 2 by reduction), attached to the corolla tube, sometimes with distinctive morphology. The gynoecium consists of 2 fused carpels (rarely 3-5) forming a compound ovary with axile placentation, typically with numerous ovules.
Fruits
Fruits are diverse within the family, primarily berries or capsules. Berries are fleshy with numerous seeds embedded in the pulp (e.g., tomato, eggplant). Capsules typically open by valves or pores (e.g., tobacco, petunia). Some genera have distinctive fruit types, such as the pyxis (circumscissile capsule) in Hyoscyamus. Seeds are typically numerous, often flattened, and sometimes with distinctive surface patterns.
Specialized Features
Many members contain diverse alkaloids, including tropane alkaloids (e.g., atropine, scopolamine), nicotine, and steroidal alkaloids (e.g., solanine). These compounds often serve as chemical defenses against herbivores. Some species have specialized trichomes that secrete sticky or toxic substances. The family shows diverse pollination syndromes, including bee, moth, butterfly, and bird pollination, with corresponding adaptations in flower morphology and color.
Field Identification
Primary Features
- Flower structure: Typically 5-merous flowers with fused petals forming distinctive shapes (rotate, funnel-shaped, tubular).
- Alternate leaves: Leaves arranged alternately on stems, often with distinctive odor when crushed.
- Fruit types: Berries or capsules with numerous seeds.
- Anther morphology: Often with distinctive anthers, sometimes opening by terminal pores or longitudinal slits.
- Sympodial growth: Many genera show a distinctive growth pattern where the main axis terminates in an inflorescence, and growth continues from a lateral bud.
Secondary Features
- Trichomes: Many species have distinctive hairs or glands on stems and leaves.
- Odor: Characteristic smell when leaves or stems are crushed.
- Calyx: Often persistent and sometimes enlarging in fruit.
- Inflorescence types: Often cymose (determinate) rather than racemose (indeterminate).
- Seed morphology: Seeds often flattened with distinctive surface patterns.
Seasonal Identification Tips
Spring: Many species begin flowering in spring. Look for the distinctive 5-merous flowers with fused petals and the characteristic alternate leaf arrangement.
Summer: Peak flowering and fruiting season for many species. Fruits developing from the persistent calyx are often distinctive.
Fall/Winter: Some species retain fruits into winter. Persistent calyces and dried fruit structures can be helpful for identification in dormant seasons.
Potential Confusion Points
- Convolvulaceae (Morning Glory family): Also has funnel-shaped flowers with fused petals but typically has twining stems, different leaf arrangement, and different fruit types.
- Boraginaceae (Borage family): Can have similar flowers but typically has alternate leaves with rough hairs and distinctive coiled inflorescences (scorpioid cymes).
- Scrophulariaceae and related families: May have similar flowers but often have opposite leaves and different fruit structures.
Notable Examples
Solanum (Nightshades, Potatoes, Tomatoes, Eggplants)
The largest genus in the family with about 1,500 species. Highly diverse in form, including herbs, shrubs, small trees, and vines. Flowers typically have rotate (wheel-shaped) corollas with distinctive anthers that often open by terminal pores and are frequently connivent (converging to form a cone). Fruits are typically berries.
Ecological/Economic Importance: Includes some of the world's most important food crops: potatoes (S. tuberosum), tomatoes (S. lycopersicum), and eggplants (S. melongena). Also includes many ornamental species and some with toxic properties. Wild species are important genetic resources for crop improvement.
Capsicum (Peppers)
Herbs or small shrubs with simple, alternate leaves. Flowers are typically white or greenish-white with rotate corollas. Fruits are distinctive berries (peppers) that vary greatly in size, shape, color, and pungency.
Ecological/Economic Importance: Major food crops worldwide, with fruits used fresh, dried, or processed. Capsaicin, the compound responsible for the pungency of hot peppers, has medicinal applications. Many ornamental varieties are cultivated.
Nicotiana (Tobacco)
Annual to perennial herbs or shrubs with simple, alternate, often sticky leaves. Flowers are typically tubular or funnel-shaped, often with long corolla tubes, and come in colors ranging from white to pink, red, yellow, or green.
Ecological/Economic Importance: Includes tobacco (N. tabacum), one of the world's most economically significant non-food crops. Contains nicotine, a potent alkaloid used as an insecticide and highly addictive stimulant. Some species are grown as ornamentals.
Petunia
Annual or perennial herbs with simple, alternate, often sticky leaves. Flowers are showy, funnel-shaped, and come in a wide range of colors. Native to South America but widely cultivated.
Ecological/Economic Importance: Among the most popular bedding plants worldwide, with numerous cultivars and hybrids. Important model organism for genetic and developmental studies in plants.
Atropa (Deadly Nightshade)
Perennial herbs with simple, alternate leaves. Flowers are bell-shaped, typically brownish-purple. Fruits are shiny black berries.
Ecological/Economic Importance: Highly toxic due to tropane alkaloids (atropine, scopolamine). Has been used medicinally in controlled doses. Atropine is used in ophthalmology to dilate pupils and has other medical applications.
Datura (Jimsonweed, Angel's Trumpet)
Annual or perennial herbs or shrubs with large, simple, often lobed leaves. Flowers are large, trumpet-shaped, and typically white to purple. Fruits are distinctive spiny capsules.
Ecological/Economic Importance: Contains tropane alkaloids with hallucinogenic and toxic properties. Has been used in traditional medicine and religious ceremonies. Some species are grown as ornamentals.
Phylogenetic Position and Evolution
The Solanaceae belongs to the order Solanales within the asterid clade of eudicots. It is closely related to the Convolvulaceae (morning glory family) and several smaller families. Molecular phylogenetic studies have helped clarify relationships within this diverse family, which has been divided into several subfamilies.
Evolutionary Significance
- Alkaloid diversity: The evolution of diverse alkaloids represents a major adaptive radiation in chemical defenses against herbivores.
- Pollination syndromes: The family shows diverse adaptations to different pollinators, including bees, moths, butterflies, and birds, reflected in variations in flower morphology, color, and scent.
- Fruit evolution: The family shows an evolutionary trend from capsular fruits to berries in several lineages, likely associated with different seed dispersal strategies.
- Habitat adaptations: Members have adapted to diverse habitats from tropical rainforests to deserts, high mountains, and temperate regions.
Related Families
Other families in the Solanales order include:
- Convolvulaceae (Morning Glory family)
- Montiniaceae
- Sphenocleaceae
- Hydroleaceae
These families share some characteristics with Solanaceae but have diverged in various ways, such as the twining habit and different fruit types of Convolvulaceae.
References and Further Reading
APG IV. (2016). An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG IV. Botanical Journal of the Linnean Society, 181(1), 1-20.
Knapp, S., Bohs, L., Nee, M., & Spooner, D. M. (2004). Solanaceae—a model for linking genomics with biodiversity. Comparative and Functional Genomics, 5(3), 285-291.
Olmstead, R. G., Bohs, L., Migid, H. A., Santiago-Valentin, E., Garcia, V. F., & Collier, S. M. (2008). A molecular phylogeny of the Solanaceae. Taxon, 57(4), 1159-1181.
Stevens, P. F. (2001 onwards). Angiosperm Phylogeny Website. Version 14, July 2017. http://www.mobot.org/MOBOT/research/APweb/
Hunziker, A. T. (2001). Genera Solanacearum: The genera of Solanaceae illustrated, arranged according to a new system. A.R.G. Gantner Verlag K.G.