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Annual or perennial vines, sometimes shrubs or small trees, commonly with milky
sap, with rhizomes or tuberous roots or stems. Leaves simple, entire, lobed, or
pinnately divided to pectinate, alternate, exstipulate. Inflorescence
determinate, cymose, or flowers solitary, axillary, with jointed peduncles.
Flowers actinomorphic, perfect, hypogynous, often large and showy, ephemeral,
usually with intrastaminal disc, generally subtended by a pair of bracts
(sometimes enlarged and forming an involucre). Calyx of 5 sepals, distinct or
sometimes basally connate, sometimes unequal, imbricate, persistent. Corolla
sympetalous, entire to slightly 5-lobed, funnelform or salverform, plicate,
brightly colored (commonly red, violet, blue, or white), indup-licate-valvate
and/or convolute (twisted) in bud. An-droecium of 5 stamens, epipetalous at
corolla base; filaments distinct, often unequal; anthers dorsifixed, dehiscing
longitudinally, usually introrse. Gynoecium of 1 pistil, 2-carpellate; ovary
superior, 2-locular or sometimes appearing 4-locular due to false septa,
sometimes with dense covering of hairs; ovules 2 in each locule, anatropous,
sessile, placentation basal or basalaxile; style simple and filiform or forked;
stig-ma(s) 1 or 2, linear, lobed or capitate. Fruit usually a 4-valved
septifragal capsule; seeds smooth or hairy; endosperm scanty, hard,
cartilaginous; embryo large, straight or curved, with folded or coiled,
emarginate to bifid cotyledons, surrounded by endosperm.
Family characterization: Vines with milky sap; showy, actinomorphic, funnelform
to salverform, plicate corolla with induplicate-valvate and/or convolute
aestivation; 5 epipetalous stamens; 2-carpellate ovary with axile placentation;
septifragal capsule; and large embryo with folded, often bifid cotyledons.
Various alkaloids and cyanogenic glycosides present. Tissues commonly with
calcium oxalate crystals. Anatomical features: articulated latex canals or latex
cells; intraxyl-ary phloem in the petiole (bicollateral bundles) and stem (Fig.
99: b); and unitegmic, generally tenuinucel-late ovules.
Distribution: Primarily in the tropics and subtropics, with representatives
having ranges extending into north and south temperate regions; particularly
abundant in tropical America and tropical Asia.
Major genera: Ipomoea (500 spp.), Convolvulus (250 spp.), Cuscuta (145—170 spp.),
and Jacquemontia (120 spp.)
U.S./Canadian representatives: 18 genera/198 spp.; largest genera: Ipomoea,
Cuscuta, and Calystegia
Economic plants and products: Edible tubers from Ipomoea batatas
(sweet-potatoes, "yams"). Powerful drugs from several, such as species of
Convolvulus (scammony, a purgative from the tubers) and Ipomoea (jalap, a
purgative from the tubers, and lysergic acid, a hallucinogen from the seeds).
Several weedy plants, such as Convolvulus (bindweed) and Cuscuta (dodder).
Ornamental plants »(species of 13 genera), including Calystegia (bindweed),
Convolvulus, Dicbondra, Ipomoea (morning-glory, cypress vine), Porana (Christmas
vine), and Stylisma.
Commentary: The Convolvulaceae have been divided into three or four subfamilies
(sometimes segregated as distinct families) and/or three to ten tribes. Although
the relationships between these groups have been generally agreed upon, the
taxonomic rank (family, subfamily, or tribe) is a matter of controversy (see
Wilson 1960). A notable segregate group, the Cuscutoideae or Cuscutaceae (a
monotypic taxon), has been separated from the rest of the Convolvulaceae by some
botanists on the basis of the parasitic habit with related specializations of
the corolla and embryo (Momin 1977).
Authors also disagree on the delimitation of the various genera within the
family, such as Ipomoea (Sen-gupta 1972). The generic lines depend upon
characters of the bracts, sepals, corolla, pollen, stigma(s), and fruit. For
example, the sepals vary in size, shape, and pubescence, and the stigmas may be
simple, lobed, or globose. In addition, seed characters (e.g., type of
pubescence) are important for species delimitation.
Morning-glories are easy to spot in the field with their twining habit and
generally large, white or brightly colored, and funnel-shaped corolla. The
corollas are twisted clockwise in bud and strongly plicate (Fig. 99: c,d; Allard
1947). Usually a flower is open for only one day (for a few hours); the corolla
then incurves as it wilts. The corolla is characteristically divided
longitudinally by five obvious demarcations that occur along the middle of the
five lobes of the limb (see Fig. 99: e). These markings taper toward the apex
and usually twist in the clockwise direction.
The flowers attract various insects (and in species of Ipomoea, birds), which
visit for the nectar secreted by the hypogynous disc (Fig. 99: j; Govil 1975).
The stamens closely surround the style by forming a short column in the center
of the flower (Fig. 99: g,h), and five narrow passages between the filament
bases lead to the nectar. The insect may touch the protruding stigma as it
enters the flower, and then it becomes dusted with pollen from the introrse
anthers as it reaches for the nectar near the base. Self-pollination may occur
when the flower wilts.
Allard, H. A. 1947. The direction of twist of the corolla in the bud, and
twining of the stems in Convolvulaceae and Dioscoreaceae. Castanea 12:88—94.
Govil, C. M. 1975. Phylogeny of floral nectary in Convolvulaceae. Curr. Sci.
Momin, A. R. 1977. Bearing of embryological data on taxonomy of Convolvulaceae./.
Univ. Bombay 44:50—65.
Sengupta, S. 1972. On the pollen morphology of the Convolvulaceae with special
reference to taxonomy. Rev. Pal-aeobot. Palynol. 13:157-212.
Wilson, K. A. 1960. The genera of Convolvulaceae in the southeastern United
States. /. Arnold Arbor. 41:298—317.