XLV. CACTACEÆ.
Succulent trees or shrubs, with copious watery juice, numerous spines springing from cushions of small bristles (areolæ), and minute caducous alternate leaves, or leafless. Flowers large and showy, perfect, usually solitary; calyx of numerous spirally imbricated sepals forming a tube, those of the inner series petal-like; corolla of numerous imbricated petals, in many series; stamens inserted on the tube of the calyx, very numerous, in several series, with slender filaments and introrse 2-celled oblong anthers, the cells opening longitudinally; pistil of several united carpels; ovary 1-celled, with several parietal placentas; styles united, terminal; stigmas as many as the placentas; ovules numerous, horizontal, anatropous. Fruit a fleshy berry. Seeds numerous, with albumen; cotyledons foliaceous; radicle turned toward the hilum.
The Cactus family with twenty genera and a very large number of species is most abundant in the dry region adjacent to the boundary of the United States and Mexico, with a few species ranging northward to the northern United States and southward to the West Indian islands, Brazil, Peru, Chile and the Galapagos Islands. Two of the genera have arborescent representatives in the flora of the United States.
CONSPECTUS OF THE ARBORESCENT GENERA OF THE UNITED STATES.
Branches and stems columnar, ribbed, continuous; leaves 0; flower-bearing and spine-bearing areolæ distinct; flowers close above spine-bearing areolæ; tube of the flower elongated; seeds dark-colored.1. [Cereus.] Branches jointed, tuberculate; leaves scale-like; flower-bearing and spine-bearing areolæ not distinct; tube of the flower short and cup-shaped; seeds pale.2. [Opuntia.]