Key to Opuntia

View taxon page for Opuntia

(For a list of species in Opuntia, use the above link.)

Jepson Manual glossary definitions can be seen by moving your cursor over words underlined with dots.

1. Stem generally velvety to minutely papillate-hairy (puberulent), or if glabrous then perianth pink-magenta, stigma white, seeds ± spheric

2. Tree < 6 m, trunks > 15 cm diam – sexually mature when young and ± shrubby ..... [O. leucotricha]

2' Shrub generally < 1 m, all or most branches ± touching the ground

3. Perianth yellow, stigma green; seed 2–3 mm ..... O. microdasys

3' Perianth pink-magenta, stigma white; seed 6.5–9 mm ..... O. basilaris

4. Spines 2–8, rigid, < 2.6 cm – c Kern Co. ..... var. treleasei

4' Spines 0, 

barbed 

Having sharp, normally downward- or backward-pointing projections. Said of an awn, bristle, or other structure.

 bristles present

5. Stem segment length < 2 × width, width > 5 × thickness ..... var. basilaris

5' Stem segment length > 2 × width, width < 2 × thickness ..... var. brachyclada

1' Stem glabrous; if perianth pink-magenta then stigma green and seeds ± flat-sided

6. Terminal stem segment generally easily detached when fresh, 2–5.5 cm, width ± = thickness; w CaRH (Siskiyou Co.) ..... O. fragilis

6' Terminal stem segments firmly attached when fresh, > 4 cm, width > 4 × thickness; mostly SW, D

7. Fruit dry in age, tan, generally spiny; perianth yellow to pink-magenta; style slender, white, base ± thicker ..... O. polyacantha

8. Spines generally pale, more numerous and hair-like, curling, 

reflexed 

Abruptly bent or curved downward or backward.

near plant base; ovary areoles 20–33; fruit generally a densely spiny bur ..... var. erinacea

8' Spines generally brown to black, 

spreading 

Oriented more or less perpendicularly to the axis of attachment; often, more or less horizontal.

to 

ascending 

Curving or angling upward from base, or about 30-60 degrees less than vertical or away from axis of attachment.

, straight, stiff on all stem segments; ovary areoles 11–21; fruit less spiny, not bur-like ..... var. hystricina

7' Fruit juicy, generally with some deep purple, spines 0; perianth yellow, orange, or red; style thick, white to red, base much thicker

9. Trunk 1, 

erect 

Upright; vertically oriented.

; areoles generally > 38 per ovary

10. Plant reaching > 3 m; stem glochids < 1 mm, inconspicuous; ovary tubercled when fresh ..... O. ficus-indica

10' Plant reaching < 2.5 m; stem glochids 2–12 mm, conspicuous; ovary smooth when fresh

11. Longest spines 19–25(50) mm; style red when fresh; seed 3.5–4 mm; SW ..... O. oricola

11' Longest spines generally 25–50 mm; style white when fresh; seed 3–6 mm; e PR, DMoj (desert mountains and lower montane slopes, canyons)

12. Spines reflexed (absent), translucent yellow throughout; seed 3 mm ..... O. chlorotica

12. Spines ± spreading, yellow apically, slightly red-brown in proximal 1/2+; seed 3–6 mm ..... O. curvispina

9' Basal branches several, ± 

decumbent 

lying mostly flat on the ground but with tips curving up.

to ascending; areoles <= 36 per ovary

13. Style and filaments white

14. Stem segment < 14 cm wide; perianth base generally pale to dark red-purple adaxially; fruit generally green inside

15. Spines mostly reflexed, all ± uniform in length ..... O. phaeacantha

15' Spines mostly spreading, lowermost 1–3 reflexed to spreading, < 1/2 length of others ..... O. ×charlestonensis

14' Stem segment > 15 cm wide; perianth base yellow adaxially; fruit red inside

16. Stem segment lightly glaucous, gray-green, generally obovate, < 20 cm wide ..... O. engelmannii var. engelmannii

16' Stem segment strongly glaucous, ± silvery-blue, round, > 25 cm wide ..... [O. robusta]

13' Style pink or filaments yellow to orange-yellow (or both)

17. Stem segment > 15 cm wide ..... O. ×occidentalis

17' Stem segment < 15 cm wide

18. Stem segment oblong-elliptic to narrowly obovate; major spines generally round, 4–11 per areole ..... O. littoralis

18' Stem segment generally obovate; major spines generally flat, generally 0–4 per areole ..... O. vaseyi

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