A. Base of flower-tube naked within. B. Ribs 20 to 50 or more.
Plant somewhat depressed; spines not long 1. L. bruchii
Plant globose to cylindric; spines very long.
Tubercles very large, 2 to 3 cm. long, 1 to 1.5 cm. high; central spines upwardly c ur ve d 2. L. ferox
Tubercles 1 to 2 cm. long or less, not over 1 cm. high; Spines slender, nearly straight.
Tubercles narrow, acute; spines subulate 3. L. longispina
Tubercles broad, blunt; spines acicular 4. L. boliviensis
BB. Ribs up to 1, but usually fewer
Flowers yellow 5. L. shaferi
Scales on flower-tube few.
Spines curved or somewhat hooked.
Central spines 4, some hooked; radial spines weak, 4 to mm. long, yellowish 6. L. cachensis
Central spine solitary, never hooked; radial spines 1 to 2 cm. long, brownish 7. L. caespitosa
Spines straight 8. L. saltensis
Scales on flower-tube numerous.
Ribs strongly undulate or broken into narrow tubercles. Inner perianth-segments broad.
Flower-areoles short-hairy; tubercles long, acute.
Spines grayish, short 9. L. cinnabarina
Spines yellowish brown, elongated 10. L. pentlandii
Flower-areoles long-hairy; tubercles short, blunt 11. L. lateritia
Inner perianth-segments narrow.
Flowers 5.5 to 6 cm. long, white-hairy 12. L. pampana
Flowers small, 3 cm. long, black-hairy 13. L. corbula
Ribs not strongly undulate, at least never tubercled. F l ower s 6 cm. long o r less.
Central spine 1 to 2.5 cm. long 14. L. andalgalensis
Central spines up to 5 cm. long, 15. L. haematantha
Flowers 10 cm. long 16. L. grandiflora
AA. Base of flower-tube with ring of hairs on inside; scales on outside of flower reflexed at apex.
Flowers yellow 17. L. thionanthus
Flowers white 18. L. chionanthus
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