They're the same plant, at least that's what I've seen for sale.

It's hard to tell without a photo if you're just sprouting a new leaf, or if it's a flower bud. The plants have to be fair-sized to bloom, so that should give you a clue, too.

HTH,

Celene

A far as I know the Oxypetalum is a epiphyllum and not a night blooming cereus because of the leaves and growth habit. Cereus leaves are not flat like epiphylum. At least that's what I've read. Here I copy and pasted. Hope this clears things up but I've only recently joined the garden web. Maybe you'll come back and read this.

Epiphyllum spp.: includes E. macropterum, E. oxypetallum. See Charles Keng's page. Epiphyllum oxypetallum is not a cereus at all, despite commonly being called "Night-Blooming Cereus." It's epiphytic, meaning it doesn't need dirt, while cereuses grow out of the ground. Also, the growth habit of Epiphyllum is different from that of the cereus spp. -- Epiphyllum has flattened leaves with wavy edges and round viny stems, while cereuses (cereii?) have thick, ridged stems, often of triangular cross-section. The flowers look similar, though.

Here is some info on the NBC not the Epiphyllum NBC

Here is a link that might be useful: NBC

Night Blooming Cereus is the common name for several plants, including Epiphyllum oxypetalum. The real Cereus, which blooms at night, is a desert cactus, as shown in the previous link. Jim Hunter's website (http://www.epiuniverse.com/modules.php?name=Night_Blooming_Cereus)has a nice write-up about E. oxypetallum. Hope this helps.
Bonnie

Here is a link that might be useful: Epiphyllum Oxypetalum