Bur Cucumber (Sicyos angulatus)

 Gourd family (Cucurbitaceae)

Description: This native plant is an annual vine up to 25' long that develops multiple lanky stems. This vine can climb over adjacent vegetation and fences using its branched tendrils, otherwise it sprawls across the ground. The stems are light green, round or furrowed, and quite hairy. The alternate leaves are up to 8" long and across (excluding the petioles). They are orbicular-angular with 3-5 shallow lobes and their margins are slightly serrated. The upper surface of each leaf is relatively hairless, while the lower surface is finely pubescent, especially along the lower veins. The petiole of each leaf is up to 5" long; it is light green, rather stout, and quite hairy. The leaf blade is strongly indented at the base where it is connected to the petiole. Occasionally, branched tendrils and racemes of flowers occur oppositely from the alternate leaves along the vine. Bur Cucumber is usually monoecious and produces both staminate (male) and pistillate (female) flowers on the same plant. Each staminate flower has a green calyx with 5 teeth, a greenish white corolla with 5 spreading lobes, and a central column of stamens that is knobby at its apex. The teeth of the calyx are short and broad with recurved tips. The lobes of the corolla have a network of green lines on a white background. The staminate flowers are individually about 1/3" across and they tend to bloom in small clusters toward the apex of the raceme. Each pistillate flower has a large ovary that is enclosed within an ovoid fruit about ½" long. The surface of this fruit is covered with sharp spines and long white hairs; it is initially green, but later turns brown. A single style is exerted from the terminal end of this fruit. The pistillate flowers are bunched together in a short raceme; a typical raceme has 3-10 pistillate flowers. The peduncles and pedicels of both staminate and pistillate racemes are green and pubescent. The blooming period occurs from late summer to early fall and lasts about 3 weeks. There is no noticeable floral scent. Each bur-like fruit contains a single large seed that is brown and flattened; this seed is tapered at one end more than the other and it has a rough surface. The root system consists of a shallow branched taproot. This plant spreads by reseeding itself.
Cultivation: The preference is full or partial sun, moist conditions, and a fertile soil that is loamy or silty. During hot dry weather, the large leaves have a tendency to droop during the middle of the day, but they usually recover at night if there is adequate moisture in the ground. The seeds germinate after the soil becomes warm.

Range & Habitat: Bur Cucumber is widely scattered across TN. Frequent. Habitats include openings in floodplain forests, moist meadows in floodplain areas, thickets, banks of ditches and rivers, and edges of fields. Moist disturbed areas are preferred.

Faunal Associations: The nectar of the flowers attracts long-tongued bees (including honeybees & bumblebees), Sphecid wasps, Vespid wasps, and various kinds of flies. Wasps are especially attracted by the accessible nectar of the staminate flowers. Some of the bees also collect pollen from the staminate flowers. Because some members of the Cucurbitaceae (Gourd family) have economic importance, their insect pests are fairly well-known. These insects feed on the roots, foliage, stems, or flowers of these vines, which includes flea beetles, Cucumber beetles, Squash beetles, plant bugs, aphids, and moth caterpillars (see the Insect Table for a listing of these species). The spiny fruits of Bur Cucumber can cling to the fur of mammals, which helps to distribute the seeds. Mammalian herbivores usually shun the foliage as a food source. The fruit is inedible.

Photographic Location: Rock Island State Park in TN

Comments: Bur Cucumber is easy to identify once it begins to flower and form fruits. It differs from Echinocytis lobata (Wild Cucumber) by its hairy stems, whereas the latter species has smooth stems. Both of these species produce bur-like fruits, but the fruits of Wild Cucumber are larger (about 2" long) and occur individually, rather than in small clusters. The staminate flowers of Wild Cucumber are usually more showy and occur on longer racemes.