Butia is a genus of feather palms from South America, particularly southern Brazil, Uruguay, Paraguay and northern Argentina.  It is somewhat of a confusing genus to sort out, since some species have a lot of variation, most of them look fairly similar to each other, and they hybridise freely.

The most common species is B. capitata, which is often considered to be one of the hardiest feather palms.  B. capitata has attractive, arching fronds, and been grown fairly extensively in the Pacific Northwest.  It is a variable palm; some individuals do not thrive very well in our cool summers, and some are more cold-hardy than others.  They also vary in their color and growth rate.  They are succeptible to spear loss in cold winters, which can be prevented by treatment with a copper fungicide.  But some Butia specimens have proven to be definitely hardy in milder areas.  Expect damage on B. capitata around -11 to -9°C/12 to 16°F.

Other species of Butia are also promising.  B. bonnettii is perhaps a form of B. capitata from a strictly botanical standpoint, but it is definitely a superior performer in our climate.  It has withstood temperatures down to -13°C/9°F without harm, and grows well in cool weather.  B. eriospatha originates farther south than B. capitata and may also be a little hardier than B. capitata.  All of these palms look fairly similar with some minor differences.  These species, along with B. archeri, B. arenicola and B. yatay, are all known to be quite hardy since they are growing in zone 8a in Alabama.  And the other species of Butia might be expected to be fairly hardy as well.  So, I would conclude that they are all worth trying in milder parts of the Pacific Northwest.  However, they do like heat and might not perform so well in cool coastal areas.