Serenoa is a genus of just one species of fan palm from the south-east USA.  It is generally a small, trunkless palm, but often forms an emergent trunk.  Some forms have spectacular bluish or silvery leaves and are very attractive.  It is very cold hardy once established; in fact, there is a 22 year old specimen of this plant in Eugene, Oregon, which is not one of the milder places west of the Cascades.  Like other southeastern palms, it likes heat and lots of summer water.  It would probably also grow in milder parts of eastern Washington.  Its hardiness increases substantially with age, so it would be worth protecting for its first few years in climates where its survival is marginal.