Horse nettle is a native perennial with spiny stems and leaves; the fruits are toxic and look like tiny yellow tomatoes. Flowers in elongated clusters (racemes) at ends of stems, white to purple, about 1 inch across with 5 united petals, forming a five-pointed star with 5 large, yellow stamens protruding. Blooms May–October. Leaves with pointed lobes (somewhat resembling red oak leaves), with 4 lateral lobes and 1 shallow terminal lobe. Does not have bristles, but stems and midribs of leaves have yellow prickles. Fruit a smooth berry, yellow when ripe, like a tiny tomato, which persists through the winter. Most parts of the plant are toxic if eaten.
Height: to 3 feet.
Occurs in waste places, rights-of-way, openings in woods, fields, prairies, and other grassy or disturbed areas. To gardeners, it is a difficult-to-control weed, but it is also one of our native grassland wildflowers. The thick stands of grasses and forbs in our native prairies compete strongly with this plant, so in its native situation, horse nettle does not overwhelm its neighbors. Where soils are disturbed, horse nettle, lacking competition, grows profusely.
Taxonomically, horse nettle is in the nightshade family (Solanaceae), which is the same family as tomatoes, eggplant, and jimsonweed. Therefore, horse nettle is not technically a "true nettle"; nettles are in a separate family (the Urticaceae). Nettles are infamous for the tiny irritating, stinging hairs on their stems and foliage.
The word "horse," as a plant adjective, implies something large, strong, or coarse. Similar plant names are horse-chestnut, a plant related to buckeyes and not in the beech family like edible true chestnuts; horse gentian, which is in the honeysuckle family and not a true gentian in the gentian family; and horseradish, which, though in the same family as radishes, is considerably stronger than them!
Horse nettle spreads easily by seed and by underground rhizomes and can be a troublesome weed, hard to pull because of its spines and deep roots. Native Americans had medicinal uses for it, but all parts are toxic if eaten, and children have reportedly been killed by eating the fruit.
Horse nettle is related to tomatoes and eggplant, whose fruits are edible because they contain a much greater percentage of carbohydrates, offsetting the presence of toxic alkaloids. Potato is also closely related, but it stores a large amount of carbohydrates in its tubers, rendering them edible. Horse nettle's fruits, however, don't store as many carbohydrates, so they contain a comparatively higher amount of the alkaloids, making them toxic to us.
Bumblebees pollinate the flowers, and a variety of insects (including predatory beetles that humans consider beneficial) feed on the leaves. Certain types of birds and some mammals eat seeds from mature fruit, but most mammals avoid them because of their toxic alkaloids.
A very simple way of thinking about the green world is to divide the vascular plants into two groups: woody and nonwoody (or herbaceous). But this is an artificial division; many plant families include some species that are woody and some that are not. The diversity of nonwoody vascular plants is staggering! Think of all the ferns, grasses, sedges, lilies, peas, sunflowers, nightshades, milkweeds, mustards, mints, and mallows — weeds and wildflowers — and many more!