What Are the Hard Round Shells on the Bottom of a Fern?

Fern Leaves

• Ferns fronds are usually compound leaves that sometimes appear quite delicate, almost like an ostrich plume. The leaves can be cut in once or twice producing an even more feathered appearance. Sometimes the fern leaves have scalloped lobes it look like many individual leaves but these leaflets are part of a compound leaf as well. Because the fern stem is rhizomous, growing underground, the leaves all arise from a central area that is actually a node on the stem. Curled, young leaves emerge from the ground and are referred to as fiddleheads because they look like the curled top of the neck of a violin or fiddle.

The Underside of the Leaf

• If you turn the fern leaves over and look at the bottom, some of the leaves will have convex rounded, white or brown dots outlining the veins of the leaf. These are the ferns sori where they form their reproductive spores. When they are newly formed, the sori are white but they darken as they mature and turn brown when they are ripe. The sori look like small hard brown shells on the bottom of the fern leaf.

Reproduction

• Ferns alternate generations between the large fern plants we are used to seeing and small heart-shaped prothallus, which rarely grow larger than 1/2 inch wide and 1/4 inch tall. The large, leafy generation of fern is called a sporophyte, because it produces spores. The sporophyte generation is vascular, enabling the fern to grow tall, while the short gametophyte generation can't move water through its system and is dependent on a wet environment to live. The short gametophyte generation produces male and female gametes. The gametophyte generation releases male gametes, or sperm, into the wet environment to find the female gametes. Once the sperm fertilizes a female egg, the merged gametes grow into a large sporophyte again.

No Flowers

• Plants produce flowers in order to attract pollinators or to act as launchpads for dispersing their pollen into the air. Because ferns have sperm that can swim and look for eggs all on their own, they have no need for, and do not produce, flowers. The downside is that ferns are restricted to areas that have surface water at least part of the year.