Plants: Silverleaf Nightshade

Silverleaf Nightshade (*Solanum elaeagnifolium*) pastel on blotter paper by Kathleen J. Hooper

Plants: Silverleaf Nightshade

Last summer, our daughter Kathleen wrote the sweetest note of thanks for our family trip to Flocks and Rocks in New Mexico. She appreciated meeting Arch McCallum, my long-admired bird watching mentor, and Brad Jeffrey, our enthusiastic geologist, for all of the fun we had exploring the areas of the Southwest together as a family. She drew the picture above, after we spotted a lot of these nightshades growing along the path in the Valley of Fires, in the Carrizozo Malpais lava flows of New Mexico.

Solanum elaeagnifolium, the silverleaf nightshade or silver-leaved nightshade, is a species of plant in the nightshade family native to North and South America. It is common in parts of southwestern USA, and sometimes weed of western North America. Other common names in the US include prairie berry, silverleaf nettle, white horsenettle, whiteweed or silver nightshade. In South Africa this nightshade is known as silver-leaf bitter-apple or satansbos (“Satan’s bush” in Afrikaans). More ambiguous names include “bull-nettle,” “horsenettle,” and the Spanish “trompillo.”[1]

Solanum elaeagnifolium was first described by A. J. Cavanilles. The plant described under the same name by W. Herbert and C. L. Willdenow based on E.G. von Steudel is Solanum aethiopicum.

Plant Description

The plant is a perennial 10 cm (3.9 in) to 1 m in height. The stems are covered with nettle-like spines less than 0.5 cm (0.20 in) long, ranging from very few on some plants to very dense on others. Leaves and stems are covered with downy hairs (trichomes) that lie against and hide the surface, giving the plant parts a silvery or grayish appearance.[1]

The leaves are up to 15 cm long and 0.5 to 2.5 cm wide, with shallowly waved edges, which distinguish it from the closely related Carolina Horsenettle (S. carolinense), which has wider, more deeply indented leaves. The flowers, appearing from April to August, have five petals united to form a star, ranging from blue to pale lavender or occasionally white; five yellow stamens and a pistil form a projecting center. The plant produces glossy yellow, orange, or red berries that last all winter and may turn brown as they dry.[1]

Plant Ecology

It can grow in poor soil with very little water. It spreads by rhizomes as well as seeds, and is common in disturbed habitats. It is very hard to control, as root stocks less than 1 cm long can regenerate into plants.

Its distribution around the globe is in the regions of Mediterranean, South Australia, South Africa, US, Mexico and South America. In the US, its range is from Kansas south to Louisiana, and west through the Mexican-border states of the United States into and in 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 the reverse. It is considered a noxious weed in 21 U.S. states and in countries such as Australia, Egypt, Greece, India, Israel, Italy, South Africa, and Zimbabwe.[2]

In a 15-year research study it was indicated that important factors for its expansion are: Elevation of 0-100m, soils with fine texture and in subsoil of medium water availability, soils with high base saturation of the topsoil and low topsoil organic carbon. Also it seems to prefer agricultural use areas, multi-lane road sides and areas near human settlements.[2]

In another study, on allelopathic effects with other plants, it was shown that white oak extract impedes its germination.

A five-year study found that frequent mowing of silverleaf nightshade contributes toward making it a ‘superweed’, with a deeper taproot, a spikier stem, and greater toxicity to grazing caterpillars.

There are several species of horse nettle, all of which have star-shaped blossoms with prominent petals, flat or turned backward, and yellow stamens. Almost all of them are prickly. Flowers of the various species are blue, purple, yellow, or white. White Horse Nettle gets its name from its covering of silvery hairs, among which are the nettle-like prickles. It grows 1-3 feet tall. The leaves are 2-4 inches long, with wavy edges. Flowers are violet-purple or white, about 3/4 inch across, with 5 petal-like lobes that are joined at the base, forming a triangular shape at the tip of each lobe. All of them have the prominent, bright yellow stamens that distinguish all the horse nettles. The yellow fruits resemble small tomatoes and remain on the plant for months. They are said to be poisonous.

The lavender, star-shaped flowers with yellow centers are beautifully set off by the silvery foliage, and large patches of the plant in full bloom are striking. However, the plant is an aggressive, poisonous weed, spreading steadily from deep rootstocks; in a few states it is classified as a noxious weed.

The genus name, from the Latin solamen (“quieting”), alludes to the narcotic properties of many species. This species is also known as Bull nettle.

Fruit & Plant Toxicity

The whole plant is toxic to both humans and livestock, even after it has dried. Ingestion of silverleaf nightshade has been implicated as a cause of ivermectin toxicosis in horses given the recommended dosage of the drug. Metabolites from the plant are speculated to disrupt the blood–brain barrier, allowing ivermectin to enter and disrupt neurotransmitter function in the brain and spinal cord.

Its thin spines can cause weed dermatitis.

The Pima Native Americans used the berries as a vegetable rennet, and the Kiowa used the seeds together with brain tissue to tan leather.