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Genus Opuntia Family Cactaceae

Description: Succulent herbs or shrubs, often much branched from the base, sometimes with a definite trunk, often spreading and forming clumps; ultimate segments mostly flat or compressed, rarely ± cylindrical; roots mostly fibrous. Areoles on segments bearing glochids, spines, hairs and flowers.

Leaves usually small, ± terete, falling early.

Flowers solitary, hypanthium bearing areoles with small leaves, spines and glochids often present. Outer perianth segments usually green passing into brightly coloured petaloid inner segments.

Fruit dry or juicy, often edible, ± ovoid, spines present or absent; seeds covered by a hard, bony aril.

Distribution and occurrence: World: c. 150 species, North & South America. Australia: 15–20 species (naturalized), all mainland States.

Many species have become established and spread in pest proportions. All species except O. ficus-indica have been declared noxious weeds in N.S.W.

Text by G. J. Harden
Taxon concept:

Taxa not yet included in identification key
Opuntia schickendantzii

 Key to the species 
1Segments mostly 2–4 cm wide, 4–10 cm long, ultimate segments usually flattened, sometimes rounded under moist conditions, stems more or less tereteOpuntia aurantiaca
Segments mostly more than 5 cm wide, and usually more than 10 cm long; all segments flattened2
2Segments finely hairy between areoles; spines mostly absent; glochids often very obvious, mostly yellow to brown, usually more than 2 mm long3
Segments glabrous between areoles; spines mostly present; glochids present, not yellow-brown, mostly less than 2 mm long
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3Shrubs mostly less than 60 cm high, usually low and creeping; segments 10–15 cm long, pubescent, areoles small, usually 5–10 mm apart; glochids 5–10 mm long, golden-brown; spines absentOpuntia microdasys
Shrubs more than 3 m high, erect; segments 15–30 cm long, tomentose to velvety; areoles larger, at least 20 mm apart; glochids yellow, 1–2.5 mm long; spines sometimes present on younger segments
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Opuntia tomentosa
4Low spreading plants, mostly less than 50 cm high; many-segmented, segments relatively small, mostly less than 12 cm long; spines mostly present on some areoles, usually whitish or brown, 5–50 mm long, or spines absent5
Erect or clumped shrubs, mostly more than 50 cm high, plants often tree-like; few-segmented and spreading in young stages, segments mostly more than 12 cm long; spines numerous, few or absent from the areoles
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5Areoles far apart, usually 4 in a diagonal line across the segment; areoles without woolly hairs, glochids scattered around edge of areoles, spines absent from many areoles or 1 erect spine, more than 30 mm long, present at some areolesOpuntia humifusa
Areoles relatively close, 5 or 6 in a diagonal line across the segment; areoles filled with brown woolly hairs, glochids restricted to upper end of areoles; spines often absent from lower half of segments, 1–3 spines less than 20 mm long mostly present on upper areoles
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Opuntia sp. sensu I.Telford (1984)
6Segments covered with spines, most areoles with at least 2 large spines, rarely only 17
Segments with relatively few spines, most areoles without spines or irregularly with only 1 or 2 spines at some areoles
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7Spines numerous, usually at least 3 at most areoles8
Spines usually 1 or 2 at most areoles on ultimate segments, rarely more
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8Areoles relatively close, 8–10 in a diagonal line across the segment; spines 3–20, the longest 2 or 3 more or less flattened, 1 or 2 reflexed bristles at the lower end of areolesOpuntia streptacantha
Areoles widely spaced, mostly 4–6 in a diagonal line across the segments; spines 2–12, all terete, reflexed bristles absent
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9Segments obovate, bright green, not glaucous; spines dark brown with age, 2–8, 2–4 cm long, sometimes to 7 cm longOpuntia elatior
Segments more or less circular, bluish green, glaucous; spines brown or yellowish at base, white above, mostly 8–12, to 5 cm long, spines sometimes absent
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Opuntia robusta
10Tree-like plant; segments bright, shiny green; spines yellowish to dark red-brownOpuntia monacantha
Spreading bushy plant, often forming large clumps; segments dull green or bluish green; spines yellow
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Opuntia stricta
11Segments glossy green, more or less spathulate; flowers more or less orangeOpuntia elata
Segments bluish to dull bluish green, rarely dull green, oblong to circular, not distinctly spathulate; flowers yellow
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12Segments usually less than 30 cm long13
Segments usually more than 30 cm long
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Opuntia ficus-indica
13Bushy, clumped plant, distinct trunks absent, clumps usually less than 1.5 m high; segments mostly less than 20 cm long, mostly dull bluish green to green but not glaucousOpuntia stricta
Tree-like plant with distinct trunk, often 2–3 m high; segments usually 20–25 cm long, bluish green, glaucous
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Opuntia robusta

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