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The families of flowering plants

L. Watson and M.J. Dallwitz

Viburnaceae Dum.

~ Adoxaceae, Caprifoliaceae, Sambucaceae.

Habit and leaf form. Small trees, or shrubs. Mesophytic. Leaves evergreen, or deciduous; small to medium-sized; opposite (mostly), or whorled (rarely); when whorled, i.e. rarely, 3 per whorl; flat; petiolate; simple; epulvinate. Lamina dissected (then lobed), or entire; if lobed, palmatifid; pinnately veined; cross-venulate. Leaves stipulate, or exstipulate. Stipules when present, intrapetiolar (small, adnate to the petiole); sometimes represented by glands. Lamina margins entire, or serrate, or dentate; flat. Vegetative buds scaly, or not scaly. Leaf development not ‘graminaceous’.

Leaf anatomy. The leaf lamina dorsiventral, or dorsiventral to bifacial. Extra-floral nectaries often present (on the petioles). Stomata anomocytic, or anomocytic and paracytic. Hairs present; eglandular and glandular (the former variously simple and unicellular or tufted, stellate, or peltate; the latter with uniseriate stalk and multicellular head). Complex hairs present, or absent; when present, peltate, or stellate. Minor leaf veins without phloem transfer cells.

Axial (stem, wood) anatomy. Cork cambium present; initially superficial. Nodes tri-lacunar (in the few species examined by L.W.). Secondary thickening developing from a conventional cambial ring.

The vessel end-walls scalariform (with many bars). The vessels without vestured pits. The axial xylem with fibre tracheids. The parenchyma apotracheal.

Reproductive type, pollination. Plants hermaphrodite, or polygamomonoecious (sometimes varying across the inflorescence?).

Inflorescence, floral, fruit and seed morphology. Flowers aggregated in ‘inflorescences’; in cymes, in corymbs, and in panicles. The ultimate inflorescence units cymose. Inflorescences terminal, or axillary; umbel-like compound corymbs, panicles and thyrses; with involucral bracts, or without involucral bracts; pseudanthial (often with the outer flowers of compact inflorescences larger and sterile), or not pseudanthial. Flowers 1– 2– bracteolate; small to medium-sized; regular; 5 merous; tetracyclic (nearly always), or pentacyclic (V. foetente). Free hypanthium absent.

Perianth with distinct calyx and corolla; 10; 2 whorled; isomerous. Calyx 5; 1 whorled; reduced, gamosepalous; five toothed; regular; persistent; non-accrescent; open in bud; with the median member posterior. Corolla 5; 1 whorled; gamopetalous; imbricate; rotate, or campanulate, or funnel-shaped, or tubular; regular; white (or cream), or pink; deciduous; non-accrescent.

Androecium 5. Androecial members adnate (to the corolla tube); all equal; free of one another; 1 whorled (nearly always), or 2 whorled (V. foetente). Stamens 5; isomerous with the perianth; oppositisepalous; alternating with the corolla members. Anthers dorsifixed; dehiscing via longitudinal slits; introrse; bilocular; tetrasporangiate. Endothecium developing fibrous thickenings. Microsporogenesis simultaneous. The initial microspore tetrads tetrahedral. Anther wall initially with one middle layer; of the ‘dicot’ type. Tapetum amoeboid, or glandular. Pollen grains aperturate; 3-celled.

Gynoecium 3 carpelled (but with only one fertile locule). Carpels reduced in number relative to the perianth. The pistil 1–3 celled. Gynoecium syncarpous; synstylovarious; inferior. Ovary 1–3 locular. Epigynous disk absent. Gynoecium more or less non-stylate. Stigmas 3; wet type; papillate; Group III type. Placentation of the only fertile locule apical; however the gynoecium is interpreted morphologically, apical. Ovules in the single cavity 1; 1 per locule (i.e., in the only fertile locule); pendulous; apotropous; with dorsal raphe; anatropous; unitegmic; crassinucellate. Embryo-sac development Adoxa-type (?). Polar nuclei fusing prior to fertilization. Antipodal cells formed; 3; not proliferating; ephemeral. Synergids pear-shaped. Endosperm formation cellular. Embryogeny asterad (?).

Fruit fleshy, or non-fleshy (i.e., sometimes more or less dry); indehiscent; a drupe (1– or spuriously 2–3 locular). The drupes with one stone (which is usually compressed). Fruit 1 seeded. Seeds endospermic. Endosperm ruminate (rarely), or not ruminate; oily. Cotyledons 2. Embryo achlorophyllous; straight.

Seedling. Germination phanerocotylar.

Physiology, phytochemistry. C3. C3 physiology recorded directly in Viburnum. Iridoids detected; ‘Route I’ type (adoxaside).

Geography, cytology. Holarctic, Paleotropical, and Neotropical. Temperate, sub-tropical, and tropical. North temperate, extending to Central America and Java.

Taxonomy. Subclass Dicotyledonae; Tenuinucelli. Dahlgren’s Superorder Araliiflorae, or Corniflorae; near Araliales (?); Cornales (?). Cronquist’s Subclass Asteridae; Dipsacales. APG 3 core angiosperms; core eudicot; Superorder Asteranae; campanulid; Order Dipsacales (as a synonym of Adoxaceae).

Species about 120. Genera 1; Viburnum.

General remarks. Differing from the sensu stricto versions of Adoxaceae and Caprifoliaceae, and from Sambucaceae, in far too many characters (involving habit, anatomy, inflorescence, floral morphology, fruit and ovule details and embryology) to be sensibly reduced to synonymy with any of them.

Economic uses, etc. Many ornamentals with showy inflorescences and attractive fruits.

Illustrations. • Technical details: Viburnum. • Technical details: Viburnum rugosum (Thonner). • Vibernum lantana (B. Ent.). • Viburnum opulus (B. Ent.). • Viburnum tinus: Bot. Mag. 2, 1788.

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, genera included in each family, and classifications (Dahlgren; Dahlgren, Clifford, and Yeo; Cronquist; APG). See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 1992 onwards. The families of flowering plants: descriptions, illustrations, identification, and information retrieval. Version: 13th March 2017.’.