Christmas fern (Polystichum acrostichoides) is a deciduous evergreen fern that grows in USDA plant hardiness zones 3-9. This particular fern is known as a Christmas fern because some parts of the plant stay green all year long. Dark green leaves, or fronds, reach up to 3 feet long and 4 inches wide. This plant brings color and interest to a garden when other plants are dormant.