1. Calystegia R. Br. (hedge bindweed)
Plants perennial
herbs, usually scrambling or twining (except in C. spithamea), with usually
deep-set rhizomes and root systems. Stems sometimes somewhat angular, glabrous
or finely hairy. Leaves mostly relatively long-petiolate (except in C.
spithamea). Leaf blades triangular to ovate or oblong-ovate, often with 1
or 2 pairs of triangular lobes at the base (then appearing sagittate or
hastate), rounded to sharply pointed at the tip, truncate to more commonly
deeply cordate at the base, the margins otherwise entire. Inflorescences
axillary, the flowers solitary or paired, long-stalked. Bracts 2, closely
subtending the flower, leaflike, longer than and more or less hiding the calyx,
slightly to strongly overlapping, ovate to oblong-ovate, persistent at
fruiting. Calyx of free sepals, these similar in size and shape, narrowly ovate
to ovate or oblong, membranous, at least toward the margins, glabrous or nearly
so. Corollas very shallowly 5-lobed, funnelform, white or rarely pink. Stamens
lacking subtending scales, not exserted. Ovary 2-locular, usually appearing
1-locular toward the tip, with 4 ovules. Style 1, the stigmas 2, oblong to
ovate in outline, somewhat flattened. Fruits globose to ovoid, 1-locular,
dehiscing longitudinally, the wall separating into 4 segments. Seeds 1–4,
oblong-ovate to ovate in outline, somewhat longitudinally angled on the inner
face, the surface smooth to very finely granular, dark brown to more commonly
black, glabrous. About 30 species, nearly worldwide.
Calystegia is now accepted by most botanists as a
genus separate from Convolvulus, although emerging molecular data
suggests that it represents merely a specialized offshoot of that genus
(Brummitt, 2002). Lewis and Oliver (1965) discussed the morphological
characters separating the two groups, including differences in pollen
morphology, stigma shape, and often locule number. The present treatment was
improved greatly following helpful discussion and advice from Richard K.
Brummitt (Royal Botanic Gardens, Kew) and Daniel F. Austin (Arizona-Sonora
Desert Museum, Tucson).
Steyermark
(1963) noted that some species of what is now considered Calystegia
apparently are poisonous to livestock, but Burrows and Tyrl (2001) do not
discuss any poisonous properties. Steyermark also noted that the group can
become noxious weeds in crop fields and disturbed sites. Hedge bindweeds do not
produce as extensive or deep a rootstock as does true bindweed (Convolvulus
arvensis), making them less significant agricultural weeds. Some species of
Calystegia are cultivated as ornamental plants on fences and trellises.