Just a warning, this plant is not a true aquatic plant and only looks good in a tank while in its infancy. Cardinal Flower is traditionally a riparian plant, growing near the shores or streams and rivers. However, it is suited to grow in a woodland setting as well. At most, cardinal flower grows in a bog, but consistently water logged roots while eventually suffocate the plant.
I've purchased one of these plants couple years back,, I had it for about a year and it actually grew out of control. In an open aquarium it create stunning blood red flowers, but it is not a true aquatic plant, and unless optimal growing conditions can be provided it will fail to grow in an aquarium shortly. In my open aquarium i had about 3watts per gallon and 6700K bulbs...
I found one of these in a creek in Kentucky submerged. It was about 2 1/2 inches tall. I didn't know what it was until now. Now it is 12 inches tall. It grew this much in about a month. So far it looks great. No flowers yet though it is still under water.
Joe