Flora of the Southeastern United States
2022 Edition

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Key to Cactaceae

1 Leaves persistent, with broad, flat, pinnately-veined blades; flowers borne in many-flowered cymes; [FL peninsula only]; [subfamily Pereskioideae]
1 Leaves absent, rudimentary (usually < 1 mm long), or caducous (lasting up to 3 months, up to 3 cm long, narrowly conical in shape, and terete or broadly elliptical in ×-section); flowers solitary; [collectively widespread in our area].
..2 Stems flattened in ×-section, at least apically (Consolea) or throughout (Opuntia) segmented into “pads” that are circular, ovate, obovate, or elliptical in outline; areoles with detachable glochids (retrorsely barbed bristles) (and also with or without spines); [subfamily Opuntioideae].
....3 Main axis of plant unsegmented, bearing ‘pads’ at its summit; fruits and flowers bearing spines; [FL peninsula only]
....3 Main axis of plant segmented throughout into ‘pads’; fruits and flowers lacking spines; [widespread in our area]
..2 Stems either cylindrical, or cylindrical but with 3-many ribs, or flattened with 2 wings and an apparent central thickened cord; areoles lacking glochids (and also with or without spines); [subfamily Cactoideae].
......4 Stems < 7 mm in diameter; plant a pendulous epiphyte; tepals <12; [tribe Rhipsalidae]
......4 Stems > 7 mm in diameter; plant either a tree, or an erect, ascending, to sprawling shrub, or an epiphyte with broadly winged stems; tepals > 12.
........5 Mature stems terete in general outline, with 8-13 rounded ribs.
..........6 Spines 6-17 per areole, 10-40 mm long; tepals linear to oblanceolate, 5-12× as long as wide; flower tube 10-20 cm long; stems unbranched to sparsely branched, ascending to sprawling, often scrambling through and supported by other vegetation; [tribe Trichocereae]
..........6 Spines 9-31 per areole; <10 mm long; tepals broadly spatulate, 2-4× as long as wide; flower tube < 1.5 cm long; stems moderately to densely branched, the branches ascending to erect, tree-like; [tribe Hylocereeae]
........5 Mature stems (2-) 3-8 angled or winged; [tribe Hylocereeae].
............ 7 Plants terrestrial, generally lacking adventitious roots
............ 7 Plants usually epiphytic or epipetric, conspicuously producing adventitious roots.