Polystichum acrostichoides - (Michaux) Schott
Christmas fern is a perennial evergreen native to eastern North America. Its range extends from Nova Scotia west to Minnesota and south to Florida and eastern Texas. It is one of the most common ferns in North America, being found within moist and shady areas in forests, rocky slopes, and stream banks. The common name of the plant is derived from its evergreen fronds which are usually still green through the end of December.
The plant grows in a circular form with all the leaves arising from a single point on the ground. It usually forms colonies but frequently grows singly or in twos or threes. In the winter the fertile leaves (leaves bearing spores) die and the sterile leaves remain through the winter but are often laid down by snow or frost. The frond is supported by a stem, which is typically about 1/4 the length of the total leaf. The stem length is given as a ratio because the leaf size can vary and its more accurate to estimate the length based on each leaf's size. The stem is black to very dark brown at the base and fades to green as it continues toward the tip. It is also covered in coarse light brown to tan scales which are typically quite short, translucentm and grooved on the upward side. As the stem continues toward the tip of the leaf the size and density of the scales decrease. The young fiddleheads (also known as crosiers) are a scaly grey and are prominent in early spring.
The fronds grow from 20 to 30 inches long and about 4 to 6 inches broad, divided into 20-35 pairs of leaflets or pinnae. Each leaflet is typically about 1 inch long and has a finely serrulate or spiny edge and is oblong to falcate (hooked like a sickle) in shape. The fine teeth or spines on the edge of the leaf point toward the tip of the leaflet. Each pinnae has a triangular lobe at its base which points toward the tip of the leaf; this protrusion is approximately 5 mm wide and equally tall and its tip bears a small spine. The lowest two leaflets are typically downward pointing and opposite to each other. The leaves are dark green and rather leathery in texture; linear to lance-like . The light brown spores are produced on leaflets that are conspicuously smaller than the leaflets below them; that being leaflets that are located at the tip of the frond.
Christmas fern resembles the Pacific Coast sword fern, but does not make the huge clumps which that fern forms, and it differs from it and most other ferns in that fertile (spore bearing) leaflets of the Christmas fern are noticeably smaller than the sterile leaflets. The fertile leaflets are identified by being covered by a brown mass and are located at the tip of the leaf.
The Christmas Fern is known to hybridize with other ferns if kept in an overlaping range.