Christmas Fern

Polystichum acrostichoides

Walking through the woods in the middle of winter it is hard to not notice the Christmas ferns.  While everything else is brown and dry, these ferns are still lustrous green, as seen in the picture at left, taken in mid-November.  For a long time, I thought the name Christmas fern celebrated that fact that it was one of the few ferns -- indeed, one of the few woodland plants-- still green at Christmas.  Or perhaps, the name came from the fact that being still green it was often used in Christmas decorations.  Recently, however, I have heard another theory.  If you look closely at the leaves, you will see that they are made of many leaflets in pairs on either side of the central stalk.  Each of these leaflets has a little "ear" pointing upward along the stalk.  These ears make the leaflet look something like a Christmas stocking as you can see in the picture below.

Christmas ferns grow in little bouquets of leaves.  The leaves stand upright in the growing season, but often tend to lie down in the winter as in the picture above, as if the plant needed to rest.  More likely this allows the plant to hide from the cold by being covered with leaves and snow.  The leaves are very variable.  In some plants, the leaves are deeply cut into smaller subleaflets.  In some plants, the leaves are spiny and resemble holly leaves --another reason they are popular as Christmas decorations.  In some plants, the leaves are crisped and wavy-edged.

The leaflets near the top of the leaf are noticeably smaller than the leaflets further down, and there is an abrupt switch from the smaller to the larger leaflets.  The smaller leaflets are fertile leaflets; if you flip them over you will find two or more rows of little brown dots, often crowded together and covering the entire underside of the leaflet.  These are the fruitdots which produce the spores.

Like all ferns, Christmas fern produces no flowers or fruits or seeds.  Instead it reproduces by  spores.  The spores are released from the fruitdots and, being microscopic, drift away on the faintest breeze.  When they land they germinate to produce a tiny plant, rarely seen, which produces eggs and sperm.  When a sperm swims to an egg during a wet spell, a new baby fern begins to grow.