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Key to families | Table of families and genera
Specimen numbers are hyperlinked to records in the Consortium of California Herbaria data view where possible. Taxa are hyperlinked to entries in the Jepson Interchange via the "[Online Interchange]" link.
Shrub, tree; roots fibrous [tuberous]. Stem: generally erect, < 6  m; segments generally flat (± cylindric), generally firmly attached; tubercles 0 to ± developed; ribs 0. Leaf: small, conic, fleshy, deciduous, present on young stems, ovaries. Spines: 0–many per areole, cylindric or flat, tip smooth or barbed, epidermis persistent; glochids generally many. Fruit: juicy, fleshy or dry; wall thick, bearing areoles; spiny or not. Seed: in a bony, ± white aril.
± 150 species: America; Opuntia ficus-indica cultivated for food, others for ornamental. (Possibly from Papago Indian name ("opun") for this food plant; or for a spiny plant of Opus, Greece) Spines smaller, fewer in shade forms; yellow spines blacken in age. Spineless stems, ovaries, and fruit generally with glochids, these occasionally long, conspicuous; hybridization common. Taxa with cylindric to club-shaped stems moved to Cylindropuntia, Grusonia.
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 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 High Cascade Range (Siskiyou Co.) ..... O. fragilis
6' Terminal stem segments firmly attached when fresh, > 4 cm, width > 4 × thickness; mostly Southwestern California, 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 near plant base; ovary areoles 20–33; fruit generally a densely spiny bur ..... var. erinacea
8' Spines generally brown to black, spreading to ascending, 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; areoles generally > 38 per ovary
10. Mature plant > 3 m; stem bristles < 1 mm, inconspicuous; ovary tubercled when fresh ..... O. ficus-indica
10' Mature plant < 2.5 m; stem bristles 2–12 mm, conspicuous; ovary smooth
11. Longest spines generally 25–50 mm; style white when fresh; seed 3 mm; e Peninsular Ranges, Desert Mountains ..... O. chlorotica
11' Longest spines 19–25(50) mm; style red when fresh; seed 3.5–4 mm; Southwestern California ..... O. oricola
9' Basal branches several, ± decumbent to ascending; areoles <= 36 per ovary
12. Style and filaments white
13. Stem segment < 14 cm wide; perianth base red; fruit generally green inside ..... O. phaeacantha
13' Stem segment > 15 cm wide; perianth base yellow; fruit red inside
14. Stem segment lightly glaucous, gray-green, generally obovate, < 20 cm wide ..... O. engelmannii var. engelmannii
14' Stem segment strongly glaucous, ± silvery-blue, round, > 25 cm wide ..... [O. robusta]
12' Style pink or filaments yellow to orange-yellow (or both)
15. Stem segment > 15 cm wide ..... O. ×occidentalis
15' Stem segment < 15 cm wide
16. Stem segment oblong-elliptic to narrowly obovate; major spines generally round, 4–11 per areole ..... O. littoralis
16' Stem segment generally obovate; major spines generally flat, generally 0–4 per areole ..... O. ×vaseyi
Citation for the whole project: Jepson Flora Project (eds.) [year] Jepson eFlora, http://ucjeps.berkeley.edu/IJM.html [accessed on month, day, year]
Citation for an individual treatment: [Author of taxon treatment] [year]. [Taxon name] in Jepson Flora Project (eds.) Jepson eFlora, [URL for treatment]. Accessed on [month, day, year].
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