Fern Parts (Frond, Segment/Pinna, Midrib and Spores/Sori)

Fern leaves are called fronds. The frond is made up of segments connecting to a midrib.

Wood Fern – drawing © John Muir Laws

Each segments can be composed of many leaflets, as shown above. This fern above is considered twice divided – once at the midrib, and again along each segment. Some ferns are 3 and 4-times divided.

Technical descriptions often refer to segments as some version of pinna (based on pinnate). Here are some variations:

· First (primary) segment – pinna (singular) or pinnae (plural)

· Second segment – pinnule

· Third segment - pinnulet

The Chain Fern in the picture below has only one leaflet for each segment, and so would be considered once divided.

Underneath the frond are reproductive spores held in sacs called sori.

Chain Fern – photo © Neal Kramer

Want more? See Wikipedia.

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