Flora of North America species comparison

obconic taproots;

secondary roots diffuse.

upper portion of primary root somewhat thickened and succulent proximally, otherwise fibrous.

top-shaped, flat-topped (aerial part sometimes hemispheric in old age or in dense subtropical vegetation), protruding above ground 0–2 × (4–)7.5–15 cm, firm;

tubercles 9–15(–20) × 3–7 mm;

axils with short wool, bristles absent;

cortex and pith not mucilaginous;

latex abundant in healthy tissue throughout cortex of stem, tubercles, and sometimes flower receptacle, sticky, white.

flat-topped or spheric to short cylindric, ± flaccid;

tubercles (5–)6–15(–17) mm;

axils appearing naked;

cortex and pith mucilaginous;

latex absent.

(8–)10–18(–27) per areole, usually brownish, darker at tip, glabrous;

radial spines (8–)10–22(–26) per areole, white to white-and-brown or brown, needlelike, 6–15(–16) mm, stiff, abaxial spines longest;

central spines (0–)1(–4) per areole, porrect or ascending, not hooked, (0.5–)2–8 × 0.15–0.45 mm;

subcentral spines 0.

19–31(–34) per areole, usually white or brown-and-white (rarely bright reddish brown), glabrous (to hoary);

radial spines (13–)15–23(–31) per areole, in 1 series, bristlelike, stiff;

central spines 1–2(–4) per areole, porrect or strongly projecting, all hooked, (7.5–)10–20(–31) × 0.2–0.4 mm;

subcentral spines 0 [several in M. barbata].

1.9–3.8 × 1.5–3 cm;

outermost tepal margins entire;

inner tepals white, greenish or cream to pale pink, with tan, pink, greenish, or brownish midstripes, 11–19 × 2–2.5 mm;

stigma lobes externally green, internally green or red (or pink), 2.5–3 mm.

(1.5–)2–3.5(–3.9) × (1.2–)1.8–3(–4.2) cm;

outermost tepal margins long fringed, reaching 1 mm;

inner tepals usually white, cream, pale tan, greenish white, or pale rose-pink, sometimes appearing pale orange proximally due to reflection of yellow anthers, usually with ± sharply defined pink midstripes (often suffused with brown, yellow, pink, red, purple, or green, darkest and brightest distally on most plants), (7.5–)12–17(–21) mm;

stigma lobes green or yellow-green.

brilliant red: scarlet, carmine, or crimson, obovoid to clavate, 10–35(–40) × 5–8 mm, juicy only in fruit walls;

floral remnant weakly persistent.

green or purple, ovoid or obovoid, (6–)10–16(–22) × (4–)6–12(–13) mm, juicy throughout;

floral remnant persistent.

reddish brown, sometimes yellowish when fresh, 1–1.2 mm, deeply pitted;

testa thin, relatively flexible;

anticlinal cell walls sinuate, interstices narrower than pit diameters;

pits cavernous or deeply concave.

chocolate brown with darker reticulation, 1.3 × 0.9 mm, pitted;

testa hard;

anticlinal cell walls straight;

interstices conspicuously narrower than pit diameters;

pits bowl-shaped.

= 22.

= 22.