CONVOLVULACEAE - Morning-Glory Family

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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.

Genera/species: 59/1,830

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.

REFERENCES CITED

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. 44:518-519.
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.