Yucca Flaccida 'Ivory Towers' is a hardy yucca to zone 5 with long sword like foliage that is variegated.  Each leaf is green with two white margins down the sides. Mature plants reach 3 feet tall and have a flower spike that can reach 4 to 5 feet with white flowers. Great for desert and rock gardens even up north.  Plants sold in 4 1/2 inch pots.