Flora of the Southeastern United States

Leaves persistent, with broad, flat, pinnately-veined blades; flowers borne in many-flowered cymes; [FL peninsula and s. TX only]; [subfamily Pereskioideae]

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].

Areoles with detachable glochids (retrorsely barbed bristles, finer than spines) (and also with or without spines), stems segmented into “pads” that are circular, ovate, obovate, or elliptical in outline and flattened in ×-section, at least apically (Consolea) or throughout (Opuntia), or into cylindric-clavate segments that are terete in ×-section (Cylindropuntia, Grusonia); [subfamily Opuntioideae].

Stems segments terete in ×-section, spines bearing papery epidermal sheaths either deciduous for the whole length of the spine (Cylindropuntia), or deciduous only at apex of spine and exposing spine tips (Grusonia); [tribe Cylindropuntieae].

Plants mat-forming, spine sheaths deciduous only at apices of spines to expose the spine tips

Stems segments flattened in ×-section to form pads, spines without papery epidermal sheaths; [tribe Opuntieae].

Main axis of plant unsegmented, bearing ‘pads’ at its summit; fruits and flowers bearing spines; [FL peninsula only]

Main axis of plant segmented throughout into ‘pads’; fruits and flowers lacking spines; [widespread in our area]

Areoles lacking glochids (and also with or without spines); stems either cylindrical, or cylindrical but with 3-many ribs, or flattened with 2 wings and an apparent central thickened cord; [subfamily Cactoideae].

Stems < 7 mm in diameter; plant a pendulous epiphyte; tepals <12; [tribe Rhipsalidae]

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.

Mature stems (2-) 3-8 angled or winged; [tribe Phyllocacteae; subtribe Hylocereinae].

Plants terrestrial, generally lacking adventitious roots

Plants usually epiphytic or epipetric, conspicuously producing adventitious roots.

Ribs 2 [-3 on proximal portions of juvenile stems], the stem margins crenate-undulate to shallowly lobed, leaf-like

Ribs [3-]4-8[-12]; stems conspicuously producing adventitious roots; [section Phyllocacteae; subtribe Hylocereinae]

Mature stems terete in general outline, tuberculate or with 4-31 rounded to keeled ribs.

Spines absent from all areoles of stems, areoles instead with dense tufts of trichomes; stems spheric-hemispheric and often depressed at apex, or rarely cylindric in deep shade (Lophophora); [s. TX only]; [section Cacteae]

Stems speckled with tufts of whitish trichomes outside of areoles; ribs [4-]8-10; inner tepals bright yellow and proximally red; [subsection Echinocactinae]

Stems not speckled with tufts of whitish trichomes; ribs 5-13; inner tepals white with pinkish midribs; [subsection Cactinae]

Spines present on at least some areoles, stems various.

Plants with at least some central spines recurved to hooked apically

Stems hemispheric to oblate; plants often buried to near flush with soil surface; [subtribe Echinocactinae]

Stems spheric to cylindrical.

Longest central spines all strongly flattened; stems 7.5-20cm in diameter; tepals bright yellow; [subtribe Ferocactinae].

Longest central spines terete or flattened only adaxially, or rarely some entirely flattened (Hamatocactus); stems 2-12cm in diameter; tepals bright yellow and proximally red-tinged or bright green to yellow-green (rarely reddish); [tribe Cacteae]

Stems with ribs thin & sharply keeled, radial spines 10-19 per areole; tepals bright yellow and proximally red-tinged; [subtribe Ferocactinae]

Stems with ribs rounded or becoming tuberculate, radial spines 13-28 per areole, tepals bright green to yellow-green (rarely reddish); [subtribe Echinocactinae]

Plants with central spines not apically-hooked, if not straight then only weakly curving downward (Coryphantha).

Long upper spines strongly flattened; [tribe Cacteae; subtribe Ferocactinae]

Spines all terete.

Stems strongly tuberculate; [tribe Cacteae; subtribe Cactinae].

Flowers borne away from stem apex, areoles lacking linear grooves

Flowers borne from stem apex, areoles with narrow, linear grooves on adaxial surfaces.

Tepals with entire margins

Tepals with fimbriate margins

Stems ribbed; the ribs rounded to sharply keeled.

Flower tube and fruit with prominent thick or bristle-like spines in addition to scales and hairs. [TX and OK only]; [tribe Phyllocacteae; subtribe Echinocereianae]

Flower tube and fruit with soft hairs or glabrous with only scales; [tribe Cereeae].

Stems < 7 cm in diameter, stems unbranched to sparsely branched, ascending to sprawling, often scrambling through and supported by other vegetation; [subtribe Trichocereinae]

Stems > 7 cm in diameter, stems unbranched to heavily branched, ascending to erect; plants tree-like; [subtribe Cereinae].

Ribs 4-7, spines of mature stems 8-10, flower tube 10 cm long

Ribs 8-13, spines of mature stems 9-31, flower tube < 1.5 cm long