CANNABACEAE (Hemp Family)

Contributed by David J. Bogler and George Yatskievych

Plants annual or perennial herbs, dioecious, sometimes aromatic, the sap not milky. Stems erect or twining, often with glandular hairs. Leaves opposite but usually alternate toward the stem tip, mostly long-petiolate. Stipules small, usually herbaceous, lanceolate to narrowly triangular, sometimes fused laterally, persistent. Leaf blades simple (and often lobed) or palmately compound, the margins sharply toothed, the surfaces with a variety of hairs and glands, cystoliths (calcium carbonate inclusions) commonly present at the base of hairs. Staminate inflorescences open axillary or less commonly terminal panicles with numerous flowers. Pistillate inflorescences dense axillary clusters or spikes, the flowers or pairs of flowers subtended by a bract and an additional closely surrounding smaller bract, these brown and scalelike at maturity, hairy and glandular. Flowers imperfect, incomplete, small and inconspicuous, hypogynous. Calyx of staminate flowers of 5 free sepals, these green or greenish white; that of pistillate flowers saclike, shorter than to nearly as long as and closely surrounding the ovary and fruit, unlobed, membranous to papery. Petals absent. Stamens 5 (absent in pistillate flowers), the filaments short, attached at or near the base of the anthers, the anthers dehiscing longitudinally. Pistil 1 per flower (absent in staminate flowers), the ovary superior, consisting of 2 fused carpels, with 1 locule, the placentation usually nearly apical. Style 1, very short, the stigmas 2, relatively long and slender, shed soon after flowering. Ovule 1. Fruits small achenes, not winged at the tip, surrounded by the persistent calyx. Seed 1, more or less spherical or nearly so (the embryo appearing curved or coiled but not always easily observed). Two genera, 4 species, North America, Europe, Asia; cultivated and introduced nearly worldwide.

Cannabis and Humulus form a natural lineage that generally is considered closely related to the Moraceae and Urticaceae, and often has been included in Moraceae. All species are wind pollinated with corresponding morphological adaptations (Miller, 1970). Staminate flowers release large quantities of wind-borne pollen, which can cause hay fever. The stigmas of pistillate flowers are elongate, exserted from the bracts, and equipped with dense, papillose hairs for catching the pollen. Dioecy in these plants is said to be regulated by inheritance of distinctive sex chromosomes, but it also is influenced by environmental conditions and seasonality, and staminate and/or bisexual flowers are produced occasionally on otherwise pistillate plants under certain conditions or toward the end of the growing season. The family is of considerable economic importance as a source of fiber from the stems, oils from the fruits, and drugs and flavorings from the glandular trichomes of the leaves and bracts.