Ted,
Your plant isn't a variety rubra.
If your label shows Ruby or similar it may be the name (cultivar).
Your plant can be:
1) C. purpurata var. semi-alba if the petals and sepals are pure white.
2) C. purpurata var. tipo (species type form) if the petals and sepals have any trace of purple color. Some people call it also var. rosea.

C. purpuratas are impressive plants with impressive flowers.
I can understand why you find them quite striking.