The third redwood, which you’ve probably never heard of is the lesser known Dawn Redwood (Metasequoia glyptostroboides), one of the oldest known tree species. This species is interesting because it had been identified only in fossils and was thought to be extinct until a grove of them was discovered in China in the middle part of the 20th century. So this is one of only a handful of tree species I know of which were around when dinosaurs roamed the planet.
The scientific name suggests to me that scientists don’t think this redwood is quite as cool as it’s record setting cousins. That, or they think it’s just too weird… which may be somewhat true. In many ways I actually think the Dawn Redwood is more similar to a Bald Cypress (also a distant relative). I’m not sure if I’ve ever seen a Dawn Redwood but they are the only redwood that will grow in Missouri so I should probably plant a few.