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2Tepals yellow with red or maroon bases adaxially.
3 Erect-spreading shrubs, chains of cladodes radiating from center of plant, the flat surface generally held perpendicular to the ground surface; cladodes remaining turgid throughout the year; stigma usually green; fruit barrel-shaped (widest near the middle); [of c. TN]
3 Spreading shrubs, plants clump forming or with chains of cladodes spreading from the central axis of the plant, the flat surface generally parallel to the ground surface; cladodes becoming cross-wrinkled during fall and winter months, fruit clavate (widest towards the tip); [collectively widespread in our area].
4 Central spines mostly 0-2 (when 2, both spines generally in the same plane, i.e., both reflexed or both erect); spinesmonomorphic (central spines only produced); [widespread in eastern US, mostly west of the Appalachian Mts. and east of the MS River]
5Cladodes generally with 1 or more spines per areole on at least some of the uppermost areoles; cladodes easily disarticulating or not; areoles typically 1-4 per diagonal row at the widest point of the cladode; [widespread in Atlantic and Gulf Coastal Plain and Atlantic Piedmont].
7 Mature plants conspicuously mat-forming; terminal cladodes often cylindrical, also sometimes obovate to elliptic (rarely completely round), 3.1-17.7 cm long, 2.0-9.0 cm wide; [NC s. to c. FL, w. to MS]
8 Seeds with funicular envelope smooth, only moderate, if any, protrusion of the cotyledons and hypocotyl, cladodes typically scalloped-margined, elliptical or rotund in outline, spines delicate, 0.7-0.9 mm in diameter; [restricted to the outer Gulf Coastal and Atlantic Coastal Plain]
8 Seeds with funicular envelope bumpy, cotyledons and hypocotyl noticeably protruding, cladodes typically smooth-margined, obovate or rotund in outline, spines stout, 0.95-1.3 mm in diameter; [of Atlantic Southern Piedmont, FL panhandle along the coast west to coastal MS and e. LA, otherwise mostly inner Gulf Coastal and Atlantic Coastal Plain]
1 Plants forming erect or ascending shrubs or small trees.
9Tepals red, pink, yellow with red midribs abaxially, or yellow with red or reddish maroon bases adaxially; stamens either thigmonastic (i.e., moving towards the stigma in response to manipulation of filaments) or not.
11 Spreading or erect shrubs; spines pale white or white with maroon or brown bands; cladodes light, glaucous green, dull; tepals yellow basally tinged red or maroon adaxially; stigmas usually greenish; fruit barrel-shaped (widest near the midpoint), not proliferous; [of nc. TN]
12Spines white (at least on second year’s growth), generally round at the base and thus round in cross section, strongly retrorselybarbed or not; glochids stramineous-colored; mature fruit red, greenish yellow or pink; [coastal and inland areas, restricted to FL]
12Spines white to yellow or gray to reddish-brown (on second year’s growth), often flattened at the base and thus lacunar or elliptical in cross section; glochids bright yellow; mature fruit usually dark purple or dark pink (red in O. ochrocentra); [of coastal areas, including FL].
13Glochid pattern generally of an adaxial crescent in the areole, i.e, glochids forming a dense fascicle in the upper portion of the areole, not widely separated throughout, exserted or not from the areole; spines yellow, sometimes with dark lateral banding; cladodes typically tuberculate with scalloped margins; [native, collectively widespread in coastal areas and also occasionally cultivated].
14Cladodes usually few-spined, spines mostly 0-3 per areole, generally straight, produced erect from the areole or only slightly spreading, usually rounded, slightly twisted, or only slightly flattened at base, yellow
15 Mature spines reddish-brown in color, prominently twisted and with conspicuous dark, red-brown bands on the lower 80% of spine; unbanded spine tips translucent to opaque and whitish-yellow; [s. FL]
15 Mature spines white, grey, or yellow, not prominently twisted or banded for most of the spine length, the marginalspines usually strongly flattened at the base, the central 1-4 spines commonly with dark brown or black bands towards the base and middle.
16 Plants densely branched; immature spines a bright, lustrous yellow, sometimes mottled or with reddish-brown bands; mature spines delicate, 4.7-5.8 cm long, the central spine(s) round or twisted in cross-section; [s. FL]
16 Plants sparsely branched; immature spines dull yellow, cream, or dull brown colored; mature spines stout, 2.2-4.2 cm long, the central spine round to flattened in cross section.
17Spines 4-13 per areole, short and mostly concealed by glochids on mature stems so that the plant appears unarmed from a distance; tepals salmon in color; [s. FL]
13Glochid pattern generally of a pin-cushion type, with the glochids widely separated and exerted from the areole; spines white with dark bases or yellow; cladodes not strongly tuberculate, the margins smooth not scalloped; [cultivated widely, and seemingly introduced in remote areas on barrier islands of SC, NC, and se. VA].