Whenever you see the word nana or its variants as part of a plant name, you can be certain that you've encountered a dwarf type (think nanotechnology). 'Nana Gracilis' hinoki cypress is no exception – after thirty-one years, this individual in the Alpine Garden has only reached two meters (6ft.) or so in height, whereas a mature individual of the wild species can reach forty meters (110ft.).
Read more about the species hinoki cypress on the conifers.org web site: Chamaecyparis obtusa.
Evolution resource link: Darwin, an online exhibit from the American Museum of Natural History.