Epiphyllum, Orchid Cactus (Epiphyllum hybrid).
Epiphyllum is native to Central America. The flowers are large, 4-6 inch-diameter, white to red, with numerous petals. Epiphyllums are very popular house plants, with numerous hybrids and cultivars produced. In fact, the term epiphyllum is commonly used to refer to these hybrids. More pictures and information of Epiphyllum at the Epiphyllum page .
If you want more information about this flower, just search the plant's Latin name on Google: