Sweet pitayas come in three types, all with leathery, slightly leafy skin:
Hylocereus undatus (Pitaya blanca or white-fleshed pitaya) has red-skinned fruit with white flesh. This is the most commonly seen “dragon fruit”.
Hylocereus costaricensis (Pitaya roja or red-fleshed pitaya, also known as Hylocereus polyrhizus) has red-skinned fruit with red flesh.
Hylocereus megalanthus (Pitaya amarilla or yellow pitaya, also known as Selenicereus megalanthus) has yellow-skinned fruit with white flesh.
Early imports from Colombia to Australia were designated Hylocereus ocampensis (supposedly red fruit) and Cereus triangularis (supposedly yellow fruit). It is not quite certain to which species these taxa refer, though the latter is probably the red pitahaya.
The fruit can weigh from 150 to 600 grams; some may reach one kilogram.