Spines nearly setaceous, most of them reflexed 171. O. chlorotica
Spines, when present, acicular to subulate. Joints spineless, or with only 1 or 2 spines at some of the areoles, or spines very short.
Corolla rotate; petals yellow.
Plant tall; spines, when present, 2 cm. long or less 172. O. laevis
Plant depressed, bushy or spreading; spines, when present, up to 7 cm. long 173. O. stricta
Corolla cup-shaped; petals salmon 173a. O. keyensis
Joints usually manifestly spiny; spines mostly 2 or more at the areoles.
Spines mostly stout, commonly flattened 174. O. dillenii
Spines acicular to subulate, terete, or slightly flattened at the base.
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