Common Fern Terms

• Auricle: – A 'ear' or lobe at the base of a pinna
• Bi-pinnate: – See 2-pinnate below
• Blade: – The portion of the frond bearing the foliage
• Costa: – Mid-vein of a pinna (plural - costae)
• Costule: – Mid-vein of a pinnule
• Crozier: – The young coiled frond - fiddlehead
• Dimorphic: – Having two different forms - such as fertile fronds having different shapes than sterile fronds.
• False indusium: – A flap of tissue on the margin of a pinna or pinnule folded over to cover sporangia
• Fertile fronds: – Those bearing spore producing organs
• Fiddleheads: – The young coiled frond - Crozier
• Frond: – The leaf of the fern bearing the pinnae - the entire above ground portion which includes the blade and the stipe.
• Gametophyte: – The prothallus, germinated from a spore, which bears the sexual organs and after cell fertilization forms a zygote, which then develops into a mature sporophyte - the 2nd life stage - the above ground spore bearing plant we call a fern.
• Indusia: – Plural of indusium
• Indusium: – The membrane covering the sorus (plural - indusia)
• Mid-rib: – The central axis (usually raised) of a frond (the rachis), pinna or pinnule (the costa).
• Pinna: – The primary division of a compound fern frond (Plural - pinnae). A distinct subdivision of the blade, when the blade segments are fully divided to the rachis.
• Pinna rachis: – The mid-vein of a pinna that comes from the major rachis of the frond
• Pinnae: – Plural of Pinna
• 1-Pinnate: – A fern frond that is once divided with the divisions extending to the rachis. In this form the pinnae are arranged on either side of the rachis, but there are no separate pinnules on the pinnae. Also referred to simply as pinnate.
• 2-Pinnate: – A fern frond that is twice divided. First the pinnae are separated from each other down to the rachis and then each pinnae has pinnules that are divided down to the costa of the pinnae. Also referred to as bi-pinnate.
• 3-Pinnate: – A fern frond that is three times divided. First the pinnae are separated from each other down to the rachis and then each pinnae has pinnules that are divided down to the costa of the pinnae and then each pinnule is divided along its central vein (costule) into separate divisions that cut down to the vein. Also referred to as tri-pinnate.
• Pinnate-pinnatifid: – The pinnae themselves are deeply divided, but not fully divided out to the tip to form separated pinnules. Pinnae can be 2-pinnate-pinnatifid and 3-pinnate-pinnatifid.
• Pinnatifid: – Deeply lobed. A blade section that is once divided but the divisions do not reach the rachis or if on the pinnae, the pinnule divisions do not reach the costa, then that pinna is said to be pinnatifid.
• Pinnule: – A secondary division of a fern blade - that is, a pinna further divided into individual sections which cut down to the costa. Portions of that pinna may not be fully cut to the costa and this pinna is then referred to as pinnate-pinnatifid.
• Rachis: – The main stalk, or central vein, of a fern frond that bears the pinnae - the blade section. The section below the pinnae is called the stipe.
• Scale: – A small piece of thin tissue that resembles a loose piece of skin - usually found on the rachis and stipe.
• Sori: – Plural of sorus
• Sorus: – A cluster of sporangia arranged on the underside or margins of the pinnae in a distinctive pattern in each fern genus (plural - sori)
• Sporangia: – Plural of sporangium
• Sporangium: – A spore case in which the spores develop. Thin walled, usually stalked. (Plural - sporangia)
• Sporophyte: – The spore bearing stage in the development of a fern. These develop from the gametophyte and become the familiar above ground fronds of the fern.
• Stipe: – Portion of the leaf stalk of the fern arising from the rhizome and below the blade.