I beleive it is the Night Blooming Cereus or Hylocereus undatus.    From Wordnik.com.  [Flower name?] Reference

They are the fruit of Hylocereus undatus and related species, known as pitayas in Spanish.    From Wordnik.com.  [Chinese feast | The Blog of Michael R. Eades, M.D.] Reference

The fruit with the crimson skin and black seeds is dragon fruit (Hylocereus cacti ) by the way, also known as pitaya (and there’s a wikipedia article on it under that name).    From Wordnik.com.  [Chinese feast | The Blog of Michael R. Eades, M.D.] Reference

It is not Hylocereus undatus.    From Wordnik.com.  [Flower name?] Reference

Pitahaya: dragon fruit (Hylocereus undatus).    From Wordnik.com.  [Exotic summer refreshment: a guide to Mexico's tropical fruit] Reference

Cereus Lemairii (Hylocereus lemairei).    From Wordnik.com.  [Cactus Culture for Amateurs Being Descriptions of the Various Cactuses Grown in This Country, With Full and Practical Instructions for Their Successful Cultivation] Reference

Cereus Napoleonis (Hylocereus trigonus).    From Wordnik.com.  [Cactus Culture for Amateurs Being Descriptions of the Various Cactuses Grown in This Country, With Full and Practical Instructions for Their Successful Cultivation] Reference

Cereus triangularis (Hylocereus triangularis).    From Wordnik.com.  [Cactus Culture for Amateurs Being Descriptions of the Various Cactuses Grown in This Country, With Full and Practical Instructions for Their Successful Cultivation] Reference

Hylocereus, both members of the cactus family.    From Wordnik.com.  [Columnist: Keith Groller] Reference