Green Pitaya
Echinocereus viridiflorus

Family: Cactus (Cactaceae)
AKA: Green-flowered Hedgehog Cactus,
 Nylon Hedgehog Cactus
Photo taken on: May 29, 2016
Location: Wet Mountains, Eastern CO
Life Zones: Plains to foothills
Habitat: Dry areas, grassy hillsides

Grows to 3" high with a round or cylindrical shape. Spines and flowers grow on vertical ridges. Flowers are greenish yellow.

Flora of North America reference.