Cactus Genus Identification Key
Plants > Cacti > Genus Identification Key
Simplified key to the identification of the major cactus genera of Southwest USA - in the cactaceae family.
1. Areoles with glochids
2. Cylindrical stem segments
2' Flattened stem segments -
opuntia1' Areoles without glochids
4. Areoles without spines or bristles -
ariocarpus4' Areoles with spines or bristles
5. Fruits and flowers with spines
6' Stems broad
7' Under 30 spines per areole, inland
5' Fruits and flowers without spines
10. Spines with conspicuous rings
11. Flower tube scales woolly and spine-tipped -
echinocactus11' Flower tube scales not woolly or spine-tipped -
ferocactus10' Spines without conspicuous rings
12. Tall stems, over 6 feet
12' Shorter stems, less than 3 feet
14. Some spines hooked
15' Only central spines hooked
16. Stems with tubercles
17. Flowers at or near stem tip
16' Stems with ribs
19. One central spine per areole, not flattened -
sclerocactus19' Up to eight central spines per areole, at least one flattened
14' No spines hooked
21' Stems with tubercles
23. Flowers in axils of tubercles
24' Flowers at or near stem tip
23' Flowers from upper edge of tubercles
27' Fewer spines, stem visible
28' Some spines flattened
29. Central spine(s) flattened; west of far west Texas -
sclerocactus29' Central spine(s) flattened or not; south Texas -
thelocactus
