While out on a walk recently, I noticed these green ferns despite the cold winter weather. Appropriate to the season, these are Christmas Ferns (Polystichum acrostichoides). Ferns are perennials, but the fronds of most ferns die back with the cold of winter. However, as will be explained below, Christmas Ferns are partially evergreen and retain their color even at Christmas-time, hence their name.
Ferns, in general have two kinds of fronds. Sporophylls produce the spores, found on the undersides of the fronds, which are involved in sexual reproduction of the fern. For a detailed explanation of fern sexual reproduction click here. Trophophylls are fronds which do not engage in spore formation, and are only there for photosynthesis. During the summer months all the fronds are present. The sporophylls are more upright and arranged in the center of the plant. The trophophylls are more flat to the ground and may be larger. During the winter months the sporophylls die back, but in Christmas Ferns the trophophylls persist (the evergreen part) and are what we see in winter. Typically, they are flat on the ground as seen in the photo. In summer, the fern looks more bushy due to the presence of the upright sporophylls. In most other ferns, both the sporophylls and trophophylls die back, and the plant survives the winter as an underground rhizome. A common example of this in the Pennypack Preserve is the Sensitive Fern (Onoclea sensibilis), so named because it is sensitive to the cold. It dies back entirely with the first cold weather of the season.
In springtime, the rhizome gives rise to new fronds which are the fiddleheads we see at that time of year. Although I don’t know what species this is, these are typical:
