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grassland pricklypear, plains prickly pear, plains twistspine pricklypear, twistspine pricklypear, western pricklypear

Habit 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.

Spines

(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

in dense tuft, pale yellow, tan to red-brown, aging brown, to 5 mm.

Flowers

inner tepals yellow with red basal portions, 25–40 mm;

filaments pale yellow;

anthers yellow;

style white;

stigma lobes cream to yellowish.

Fruits

green to yellowish to dull red, stipitate, elongate-obovoid, 25–40 × 15–28 mm, fleshy, glabrous;

areoles 16–28.

Seeds

tan, subcircular, 4–5 mm, thickish, warped;

girdle broad, protruding to 0.5 mm.

2n

= 44.

Opuntia macrorhiza

Phenology Flowering late spring (May–Jun).
Habitat Plains, chaparral, grassy woodlands, coniferous forests, sandy to loamy soils
Elevation 100-2300 m (300-7500 ft)
Distribution
from FNA
AR; AZ; CO; KS; MO; NM; OK; TX; UT; Mexico (Chihuahua)
[WildflowerSearch map]
[BONAP county map]
Discussion

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.
Parent taxa Cactaceae > subfam. Opuntioideae > Opuntia
Sibling taxa
O. aciculata, O. atrispina, O. aurea, O. aureispina, O. basilaris, O. chisosensis, O. chlorotica, O. cubensis, O. ellisiana, O. engelmannii, O. ficus-indica, O. fragilis, O. humifusa, O. littoralis, O. macrocentra, O. microdasys, O. oricola, O. phaeacantha, O. pinkavae, O. polyacantha, O. pottsii, O. pusilla, O. rufida, O. santa-rita, O. stricta, O. strigil, O. tortispina, O. triacantha, O. ×columbiana, O. ×curvispina, O. ×occidentalis, O. ×spinosibacca, O. ×vaseyi
Synonyms O. compressa var. macrorhiza, O. mesacantha var. acrorhiza
Name authority Engelmann: Boston J. Nat. Hist. 6: 206. (1850)
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