Actually, they do bloom but the blooms are the same color as the rest of the plant. You really have to look close to see them. Also, WH's produce seeds. 
Just call me Mr. Invasive Species. 
The flowers are dioecious (requiring male and female), and are hidden in the middle of the plant amongst the leaves. Small green berries form after successful fertilization. The plant can also undergo asexual reproduction. Mother and daughter plants are connected by a short stolon, forming dense mats. This is the normal method of reproduction in non-tropical zones.
Invasive is not the word for it. From the Nile near Lake Victoria in Africa, it is now present, either naturally or through human introduction, in nearly all tropical and subtropical fresh waterways.
