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Sori

Lady Fern Spores Maturing

Ferns are non-flowering plants which reproduce by spores, not seeds, and have a vascular system that transports fluids (unlike mosses, algae and liverworts).  Spores are typically located inside a capsule, or sporangium.  In many species of ferns, clusters of sporangia, called sori, are borne on the underside or margins of their fronds.  Often an indusium, or protective flap of tissue, covers each sorus, protecting the developing sporangia.  If you like to be able to give a fern a name, you will find that the shapes and arrangement of sori are a valuable identification tool.

Northern Lady Fern, Athyrium filix-femina, is a fairly common fern found in moist woods, swamps, thickets and fields.  It appears quite lacy and often grows in a somewhat circular cluster.  There are two distinguishing characteristics which are particularly helpful in recognizing Lady Fern.  One is its eyebrow-shaped sori.  If you look on the underside of a spore-bearing frond you will find that each sori is slighted curved, or arched, like an eyebrow.  The other diagnostic feature is the scattered thin, dark brown scales that are found on the stipe – the section of the fern’s stem between the ground and where the leafy frond begins.

This time of year, when the spores of many fern species are maturing, is a good time to learn the different ferns in the Northeast.  There are many excellent field guides to ferns.  One that you can easily tuck into your pocket is Lynne Levine’s Identifying Ferns the Easy Way.

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