Vallisneria species?

I'm not sure what species this is. I'm not even sure it's Vallisneria, though it was sold to me as Dwarf Val. It grows in very compact clumps, usually 4" to 6" high, but occasionally some of the plants get much higher - about 12". The flower stalk is very long, trailing over the surface of the water, and is branched, with multiple buds, each on its own long stem. The buds at the tip of the stalk bloom first.