CANNABACEAE (Hemp Family)
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
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.