Perennial vine 1 - 4 m long Stem: strongly twisting, climbing or twining, elongate, more or less hairless (but varies by subspecies), and arising from a rhizome. If the stem is cut or broken, it exudes a milky sap. Leaves: alternate, long-stalked (stalks 5 - 15 cm), non-toothed, usually hairless above, sometimes short-hairy below, 5 - 10 cm long, longer than wide, arrowhead-shaped with two short basal lobes spreading or curved slightly downward. Flowers: many, singly in leaf axils, long-stalked (longer than leaf stalk), pink or white, showy, 3 - 7 cm long, radially symmetric, tubular to funnel-shaped. Each flower is immediately subtended by two, large (1 - 3 cm long, 0.5 - 2 cm wide), non-toothed, somewhat egg-shaped or oblong, pointed- or somewhat blunt-tipped, and sometimes slightly ridged (keeled) bracts which hide the sepals. Sepals: five, green, egg-shaped to lance-shaped, but usually obscured by larger subtending bracts. Petals: five, but fused into a long tube with expanded to flaring limb, which may be shallowly five-lobed or merely wavy along edges. Stamens: five, attached to inside base of petal tube, then separating for 1.5 - 3.5 cm with 4 - 6.5 mm long anthers, but not extending beyond petal tube. Pistil: with one, single-chambered, superior ovary; and a single, slender style which ends in two oblong, blunt, and somewhat cylindric stigmas. Fruit: stalked, several-seeded, single-chambered, rounded capsules.
Similar species: Calystegia sepium is most easily confused with C. silvatica ssp. fraterniflora, but that taxon has sharply angled and winged flower stalks which are typically not longer than the subtending leaf stalk, the leaves are hairy on both sides, the bracts are larger and much wider (2 - 4 cm long, over 1.5 cm wide), and the flowers are usually well over 5 cm long. There are at least eight subspecies of C. sepium, three of which have been collected in the Chicago Region. The most common entity in the Chicago Region is C. sepium ssp. americana, which can be distinguished by a sharp, V-shaped angle between the two basal lobes of the leaves, a long tapering pointed leaf tip, a bright pink flower, and normally somewhat hairy stems, leaf stalks, and flower stalks. A more western taxon, C. sepium ssp. angulata (which is very similar to the European C. sepium ssp. sepium), has been reported a few times in the Chicago Region. It can be distinguished from the other subspecies by its white flowers, hairless stems, and spreading basal leaf lobes with distinct angles between the lobes and leaf sides, but with a wider, almost U-shaped area between the lobes at the base of the leaf. The third subspecies reported in the Chicago Region, C. sepium ssp. erratica, is more rare, only definitively reported once, though the type specimen is from Richland County, Illinois, well south of our area. This subspecies is quite different from the other subspecies since the bracts and sepals are not clearly differentiated so they appear as a single spiral whorl, it has abruptly truncated leaves, and downward pointed, basal lobes with almost no space between the lobes.
Flowering: June to September
Habitat and ecology: Very common, especially in open sunny places, in a wide variety of habitats including pastures, open weedy ground, meadows, and even prairies.
Occurence in the Chicago region: native
Notes: There is much variation in this species and most of the variability has been used to distinguish many subspecies. Most of the character differences have to do with leaf shape and hairiness of stems and leaf and flower stalks, but stamen measurements are also important.
Etymology: Calystegia is a combination of the Greek word kalyx meaning the whorl of sepals (calyx) of a flower, and stegon, meaning cover; together referring to the bracts that conceal the calyx. Sepium means "of hedges or fences", in reference to the common occurrence of the plant on fences and within hedges due to its twining and climbing nature.
Twining or occasionally trailing, to 3 m; lvs long- petioled, triangular to oblong in outline, hastate or sagittate, 5-10 cm; peduncles 5-15 cm; fls solitary; bracts ovate or oblong, 1-2 cm, commonly cordate at base; cor pink or white, 4-7 cm; 2n=22, 24. Thickets, shores, and disturbed sites; temperate regions of N. Amer. and Eurasia. We apparently have both native and intr. forms. Many confluent vars. have been described. (Convolvulus s.)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.