This small Cyathea from New Zealand is regarded as New Zealand's most cold-hardy tree fern.  It grows at rather high elevations and shows a definite preference for cool climatic conditions.  It usually has the habit of creeping along at ground level rather than forming an upright trunk, and therefore may not qualify as a "true" tree fern in the opinion of some.  The fronds are small, broad and shiny.

I am not aware that it is in cultivation outside of New Zealand, but it should certainly be introduced.  Perhaps it could be coaxed into growing an upright trunk in an ideal garden situation with copious amounts of fertilizer and water.  Even in the wild, some individuals have been known to grow some upright trunk.  They are accustomed to partial shade and a moist soil.