About Solanum elaeagnifolium Cav.
Solanum elaeagnifolium Cav. is a perennial plant that grows between 10 cm (3.9 in) and 1 m in height. Its stems are covered with nettle-like spines shorter than 0.5 cm (0.20 in); spines range from very few on some plants to very dense on others. Both leaves and stems are covered with downy lying trichomes (hairs) that cover the plant surface, creating an overall silvery or grayish appearance. Leaves can grow up to 15 cm long and 0.5 to 2.5 cm wide, with shallowly wavy edges; this leaf shape distinguishes it from the closely related Carolina Horsenettle (S. carolinense), which has wider, more deeply indented leaves. Flowers bloom from April to August, with five united petals forming a star shape that ranges in color from blue to pale lavender, and is occasionally white. Five yellow stamens and one pistil form a projecting central structure. The plant produces glossy yellow, orange, or red berries that persist through the winter, and may turn brown as they dry.
This species can grow in poor soil with very little water. It spreads through both rhizomes and seeds, and is common in disturbed habitats. It is very difficult to control, because root fragments shorter than 1 cm can regenerate into full new plants. It is distributed globally across the Mediterranean region, South Australia, South Africa, the United States, Mexico, and South America. In the United States, its range extends from Kansas south to Louisiana, and west through the U.S. states along the Mexican border into Mexico. In South America, it is found in Uruguay, Argentina, and Chile. It may have originated in North America and been accidentally introduced to South America, or vice versa. It is classified as a noxious weed in 21 U.S. states and in countries including Australia, Egypt, Greece, India, Israel, Italy, South Africa, and Zimbabwe.
A 15-year research study identified key factors that support this species' expansion: elevation between 0 and 100m, fine-textured soils with medium water availability in the subsoil, high base saturation in topsoil, and low organic carbon in topsoil. It also tends to prefer areas used for agriculture, the sides of multi-lane roads, and areas near human settlements. A separate study on allelopathic interactions between this species and other plants found that white oak extract impedes its germination. A five-year study found that frequent mowing of silverleaf nightshade contributes to it becoming a 'superweed', developing a deeper taproot, a spikier stem, and greater toxicity to grazing caterpillars.
The entire plant, even when dried, is toxic to both humans and livestock. Ingestion of silverleaf nightshade has been linked to cases of ivermectin toxicosis in horses that received the recommended dosage of the drug. It is hypothesized that metabolites from the plant disrupt the blood–brain barrier, allowing ivermectin to enter and interfere with neurotransmitter function in the brain and spinal cord. The plant's thin spines can cause weed dermatitis. Historically, Pima Native Americans used the plant's berries as a vegetable rennet, and Kiowa people used its seeds combined with brain tissue to tan leather.
