Fuzzy Brown Spots on My Staghorn Fern

The Staghorn's Sporangia

• On the undersides of the staghorn fern leaves are structures called sori. These sori hold what are known as sporangia, which are stalks tipped with bulbous structures for holding spores. The staghorn fern's sori and sporangia are brown and could certainly be seen as fuzzy. As the spores mature they push out on the tips of the sporangia and, eventually, they will burst open, releasing the spores into the wind or water. Spores are small and may look like a cloud of dust if you happen to pass by when they're released.

The Prothallus

• When a spore reaches a spot with just the right conditions, they germinate. Staghorn ferns are epiphytes and will germinate within tree bark. A germinating spore grows into a small, heart-shaped structure called a prothallus. At the bottom, or pointed end, of the heart are root-like rhizoids that help supply water and nutrients. Among the rhizoids are the male reproductive organs, called antheridia. At the top of the prothallus, the rounded portion of the heart, are the female reproductive organs, called the archegonia.

Fertilization

• Once the prothallus is mature, sperm are released from the antheridia. The sperm must have water present to swim. Sperm swim for the archegonia, ideally, of a different prothallus than the one from which they came. Sperm can fertilize the eggs of their own prothallus, but it is better for genetic diversity if they don't. Once they reach the archegonia, they swim down and fertilize the egg. The fertilized egg becomes a zygote and, eventually, an embryo.

The Young Fern

• As the embryo grows it will form its first, very small fronds and the prothallus will wither and die. Young ferns often look moss-like before they have matured enough to produce full-sized fronds. The staghorn is unique among ferns because it produces two kinds of fronds. Its upper fronds are sterile, rounded and clasp onto the tree where the fern clings. The lower fronds are the fertile, spore producing fronds with the thick branching characteristic of staghorns.