I was looking through some old vacation pictures and came across this one. It sure gives a perspective on how big these trees are.
Sequoiadendron is the giant redwood, coastal redwood is the tallest, it's unique in that it's a hexaploid which rare for a gymnosperm, except ephedra plants. Scientist speculated it's because it evolved from its self(cloning behaviour) although it's capable of outcrossing too. The final genus is the metaseaquoia, the Chinese dawn redwood