# 6.2.2: Ferns

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## Gametophyte Morphology

Fern gametophytes are reduced, thalloid, and heart-shaped. They are often referred to as a prothallus or prothallium.

## Sporophyte Morphology

Fern sporophytes are composed of megaphylls, often pinnately compound fronds that emerging as fiddleheads in the spring. Sporangia are produced in clusters called sori (sorus, singular) on the fronds.

### Circinate Vernation

Circinate vernation is a term used to describe the development of the fern fiddlehead into a frond. Because plants grow apically, it is important to protect the apical meristems in growing organs (as we have seen in both axillary and terminal buds with the evolution of bud scales). The fiddlehead is essentially a structure that tucks away the growing tips of the fronds. As the frond develops, it gradually unfurls, releasing the tips last.

### Sori

A sorus (plural, sori) is a cluster of sporangia, often protected by an umbrella-like structure called the indusium as the spores mature. Each sporangium is lined by an inflated strip of cells called an annulus. When the spores have matured, the cells in the annulus begin to dry out, causing the cells to collapse and pull the sporangium open, releasing the spores.

## Full Life Cycle Diagram

Note: Images by Jon Houseman are licensed in Wikimedia as CC BY-SA. In an email with Maria Morrow, he agreed that we could use the CC BY-NC license for these images.

This page titled 6.2.2: Ferns is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by Maria Morrow (ASCCC Open Educational Resources Initiative) .