Morphogenesis of Capitate Glandular Hairs of Cannabis Sativa (Cannabaceae)

The glandular secretory system in Cannabis sativa L. (marihuana) consists of three types of capitate glandular hairs (termed bulbous, capitate‐sessile, and capitate‐stalked) distinguishable by their morphology, development, and physiology. These gland types occur together in greatest abundance and developmental complexity on the abaxial surface of bracts which ensheath the developing ovary. Bulbous and capitate‐sessile glands are initiated on very young bract primordia and attain maturity during early stages of bract growth. Capitate‐stalked glands are initiated later in bract growth and undergo development and maturation on medium, to full sized bracts. Glands are epidermal in origin and derived, with one exception, from a single epidermal initial. The capitate‐stalked gland is the exception and is of special interest because it possesses a multicellular stalk secondarily derived from surrounding epidermal and subepidermal cells. Glands differentiate early in development into an upper secretory portion and a subtending auxiliary portion. The secretory portion, depending on gland type, may range from a few cells to a large, flattened multicellular disc of secretory cells. The secretory portion produces a membrane‐bound resinous product which caps the secretory cells. Capitate‐stalked glands are considered to be of particular evolutionary significance because they may represent a gland type secondarily derived from existing capitate‐sessile glands.