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Key to Opuntia

Cactaceae

Opuntia

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1 Plants forming low, spreading shrubs.
  2 Tepals 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); spines monomorphic (central spines only produced); [widespread in eastern US, mostly west of the Appalachian Mts. and east of the MS River]
      4 Central spines mostly 0-3 per areole (when 2-3, the lower spines generally reflexed and the upper spine porrect on upper cladodes); spines monomorphic (central spines only) or dimorphic (with smaller hairlike radial spines and larger central spines); [mostly west of the Mississippi River, in our area as a rare disjunct in w. MS]
  2 Tepals entirely yellow or greenish yellow.
        5 Cladodes spineless; cladodes never easily disarticulating; areoles typically 4-5 per diagonal row at the widest point of the cladode; [central Appalachian Mts. and n. Atlantic Coast, disjunct in nc. MS]
        5 Cladodes 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].
          6 Terminal cladodes easily disarticulating, cylindrical or moderately flattened; spines strongly retrorsely barbed to the touch, disposed from areoles in the same plane; terminal cladodes with 1-3 areoles per diagonal row at the widest point of the cladode
             7 Mature plants cespitose, forming low clumps or shrubs; terminal cladodes rotund to obovate, 3.2-13.5 cm long, 2.4-6.7 cm wide; flower bud apices round; [FL keys]
             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]
          6 Terminal cladodes disarticulating (sometimes falling easily later in the season), 3.1-17.7 cm × 2-9 cm, strongly flattened; spines retrorsely barbed (to the touch) or not; cladodes with 3-4 areoles per diagonal row at the widest point of the cladode.
               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.
                 9 Tepals 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.
                   10 Cladodes generally spineless; tepals red or pink, erect; stamens and style exserted past the corolla; filaments red or pink, the stamens not thigmonastic; [exotic, rarely persistent or naturalizing in FL]
                   10 Cladodes generally spiny; tepals yellow and variously tinged red or maroon adaxially or abaxially; stamens and style included within the corolla; filaments yellow or yellow green, the stamens thigmonastic.
                     11 Erect shrubs or small trees; spines chalky-white; cladodes dark, glossy green; tepals yellow with red abaxial midrib; stigmas white to cream; fruit clavate (widest towards the tip), often proliferous; [exotic, known from FL only in our area]
                     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]
                       12 Spines white (at least on second year’s growth), generally round at the base and thus round in cross section, strongly retrorsely barbed or not; glochids stramineous-colored; mature fruit red, greenish yellow or pink; [coastal and inland areas, restricted to FL]
                       12 Spines 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].
                          13 Glochid 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].
                            14 Cladodes 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
                            14 Cladodes spiny throughout, the spines 0-13 per areole, curved and spreading from the areole margins, OR stiffly porrect, or mostly concealed within glochids
                              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 marginal spines 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.
                                  17 Spines 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]
                                  17 Spines 0-11 per areole, conspicuous on mature stems, curved and spreading from the areole; tepals bright yellow; [NC s. to s. FL, w. to AL]
                          13 Glochid 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].