Opuntia macrocentra |
Opuntia macrorhiza |
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black-spine pricklypear, nopal violaceo, purple pricklypear |
grassland pricklypear, plains prickly pear, plains twistspine pricklypear, twistspine pricklypear, western pricklypear |
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Habit | Shrubs, erect to decumbent, to 1 m. Stem segments not easily detached, purple (particularly under stress) to green with purple near areoles and margins of stem segment, flattened, broadly obovate to subcircular, thickish, 7–20 × 6–18 cm; areoles 6–8(–10) per diagonal row across midstem segment, elliptic to circular, 3–7 × 2.5–5 mm; wool tan to whitish, aging black. | Shrubs, forming clumps, 7.5–16 cm, sometimes from tuberlike rootstocks. |
Stem | segments not easily detached, dark dull green, often cross wrinkled when stressed, flattened, obovate to circular, 5–11 × 3.5–7.5 cm, fleshy (to flabby and cross wrinkled when stressed), tuberculate, glaucous; areoles 5–6(–8) per diagonal row across midstem segment, oval to subcircular, 2–4 mm diam.; wool tan. |
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Spines | 0 or 1–15+ per areole, few and at distal areoles or many and on most areoles, usually erect to spreading, appearing unruly, sometimes deflexed, straight or curving, acicular, often flexible, subterete to flattened basally; longer ones reddish brown to ± black (rarely yellow to red in w Texas), or partly to wholly white, 30–120(–170) mm; reflexed spine rarely present, 1 in some areoles, short, whitish. |
(0–)1–4 per areole, usually in distal areoles, erect to spreading, white to red-brown, acicular, straight, terete or 1 flattened, ± stout (0.5 mm diam. at base), longest to 60 mm. |
Glochids | dense in crescent at adaxial edge of areole and well-developed subapical tuft, reddish yellow, aging brown, 2–3(–6) mm. |
in dense tuft, pale yellow, tan to red-brown, aging brown, to 5 mm. |
Flowers | inner tepals yellow with red basal portions, obovate-apiculate, 25–40 mm; filaments and anthers yellowish; style cream; stigma lobes green. |
inner tepals yellow with red basal portions, 25–40 mm; filaments pale yellow; anthers yellow; style white; stigma lobes cream to yellowish. |
Fruits | red to purplish, obovoid to barrel-shaped, 25–40 × 20–23 mm, fleshy or ± juicy, glabrous, spineless; umbilicus 8–10 mm deep; areoles 22–44. |
green to yellowish to dull red, stipitate, elongate-obovoid, 25–40 × 15–28 mm, fleshy, glabrous; areoles 16–28. |
Seeds | yellowish, suborbicular to reniform, angled, 5–7 × 3.5–5 mm, sides flattened; girdle protruding 0.8–1.2 mm. |
tan, subcircular, 4–5 mm, thickish, warped; girdle broad, protruding to 0.5 mm. |
2n | = 22, 44. |
= 44. |
Opuntia macrocentra |
Opuntia macrorhiza |
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Phenology | Flowering spring (Mar–Jun). | Flowering late spring (May–Jun). |
Habitat | Desert uplands, grasslands, oak woodlands, sandy desert flats, rocky hills and valleys | Plains, chaparral, grassy woodlands, coniferous forests, sandy to loamy soils |
Elevation | 900-1600 m (3000-5200 ft) | 100-2300 m (300-7500 ft) |
Distribution |
AZ; NM; TX; Mexico (Chihuahua, Coahuila, Sonora)
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AR; AZ; CO; KS; MO; NM; OK; TX; UT; Mexico (Chihuahua)
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Discussion | Opuntia macrocentra var. minor is represented by relatively short and compact shrubs with a glochid pattern of a dense crescent in the adaxial edge of the areoles like the species and a much taller tuft of spreading glochids. This variety, which grows along the western side of the Rio Grande in Big Bend, Texas, appears best interpreted as a tetraploid hybrid between tetraploid putative parents, Opuntia macrocentra and O. tortispina. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Opuntia macrorhiza hybridizes with the hexaploid O. engelmannii (apparently var. lindheimeri) forming the pentaploid O. ×edwardsii V. E. Grant & K. A. Grant. This hybrid is a small subshrub, 20–40 cm, with a mixture of widely spaced, unequal glochids and closely spaced, shorter glochids. Its major spines are gray, and its tepals are yellow or yellow with red bases. Those characteristics are similar to one parent or the intermediate of the two putative parents reported from Blanco and Guadalupe counties, central Texas. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
Source | FNA vol. 4. | FNA vol. 4. |
Parent taxa | Cactaceae > subfam. Opuntioideae > Opuntia | Cactaceae > subfam. Opuntioideae > Opuntia |
Sibling taxa | ||
Synonyms | O. violacea, O. violacea var. castetteri, O. violacea var. macrocentra | O. compressa var. macrorhiza, O. mesacantha var. acrorhiza |
Name authority | Engelmann: Proc. Amer. Acad. Arts 3: 292. (1856) | Engelmann: Boston J. Nat. Hist. 6: 206. (1850) |
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