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May 23, 2014 · Division of fern fronds. The lamina of a frond is often divided into many pinnae along the length of the rachis. The pinnae can also be divided into many pinnules. If lamina is divided only into pinnae but the pinnae are not divided into pinnules then a frond is known as being pinnately divided.
Parts of a fern frond The large ferns in this guide are arranged by the number of times the frond is divided – the example here is twice-divided, or bi-pinnate. After the large ferns there are two smaller woodland ferns, and then four ferns commonly found on walls. Stipe: the stalk of the frond Pinna (plural = pinnae) Croziers Rachis: the mid-
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In Athyrium filix-femina, some individuals have twice-divided fronds and others have three-times-divided fronds. In Cystopteris fragilis, the fronds are twice-divided but the margins of the pinnules of some individuals are so deeply cut that they appear to be three-times-divided.
- Leaves. The leaves of ferns are often called fronds. Fronds are usually composed of a leafy blade and petiole (leaf stalk). Leaf shape, size, texture and degree of complexity vary considerably from species to species.
- Fiddleheads. As new fronds emerge, generally in the spring, they unroll, these unrolling fronds are called fiddleheads. Fiddleheads of Alaska hollyfern (Polystichum setigerum) just beginning to unroll.
- Leaf Divisions. Depending on the species, fern leaves display a wide array of divisions. Various degrees of leaf divisions are shown in this series of frond silhouettes.
- Dimorphic Fronds. Some ferns have two kinds of fronds: fertile fronds (leaves with sporangia) and sterile fronds (leaves lacking sporangia). Ferns with two kinds of leaves are referred to as dimorphic.
Divided fronds: pinnate, bipinnate. Most ferns have divided fronds. These may be once-cut (pinnate), twice cut (bipinnate), three times cut (tripinnate and so on.
Sep 24, 2010 · The basic divisions of the frond. Pinnae or leaflets may be arranged alternately or in opposite pairs along the midrib. If the frond is once divided, then it is 'pinnate'. More commonly fronds are divided into secondary pinnae and are 'bipinnate', or into tertiary pinnae and are 'tripinnate'. Image acknowledgement: Steve Attwood. Koru
The following structures are found: the pinnae (the primary divisions of the leaf), pinnules (the ultimate divisions of the leaf), the petiole (the bare stalk of the frond) and the rachis (the extension of the petiole to which the pinnae are attached).
