• Trichocereus genus from South America

Trichocereus grandiflorus

• Echinopsis genus from South America

Echinopsis candicans

• Hylocereus genus from Central America

Commercially available Hybrides such as Hylocereus x Epiphyllum can produce flowers that measure some 30 cm across.

• Selenicereus grandiflorus, Southern Mexico

This is the largest cactus flower of them all when looking at a true species, not a hybrid. They are night-blooming and can measure up to 35 cm across an long, more than a foot. Their flowers have a sultry vanilla-like smell to them.

• Peniocereus greggii from Northern Mexico and New Mexico, USA

• Echinocereus genus from Northern Mexico and the U.S. Southwest

Echinocereus scheerii

Echinocereus dasyacanthus (Western Texas, Southern New Mexico)

The largest Echinocereus flowers I have seen measure some 20 cm across when they are fully open such as from Echinocereus scheerii. Echinocereus is flowering during the day, whereas all other examples flower overnight.