Time to take a shallow, messy dive into What’s That Fern? First, some terms that might be helpful and a diagram that maybe isn’t. (It helped me, though. Enjoy!)
Frond: full structure from the ground up.
Stipe: the “stem” or “stalk” on the frond that stretches from the ground to the “leaves” or pinnae (below). Petiole is sometimes used, as it is in other plant structure – the branch of a stem that ends in a leaf.
Rachis or blade: the part of the frond above the stipe where pinnae appear.
Stalk: Colloquially, the stipe and rachis can be referred to as the stalk, but for identification purposes it may be advantageous to describe them as separate structures.)
Pinna (PIN-uh) (singular) or pinnae (PIN-ee) (multiple)- analogous to the full leaf of a plant. On ferns can be thought of ‘these are the leaves that have sub-leaves’ – a single feathery part of the many feathery parts attached to a single frond. Some ferns, like Christmas ferns, are not further divided, and are described as as simply pinnate.
Costa: The ‘stem’ or ‘petiole’ type structure between individual pinnae.
Apex: The end point of a frond.
Pinnule(s) – the subsection of pinna that can be thought of as sub-leaves of pinna. More complicated, lacier ferns have pinna that are divided two or more times, resulting in soft, billowy textures when massed, as in this delicate Lady Fern below:
Lobes: the undulating curves of a single pinna. If the pinna flow around the rachis (the stem) without ever touching it, that frond is described as pinnatifid:
To recap:
Reproductive structures:
Spores: the barely-visible reproductive material, analogous to seeds.
Sori (SORE-eye) (multiple) or sorus (SORE-us) (singular) – the reproductive structures that contain the spores.
Some ferns, such as cinnamon fern, may have sterile fronds and one or more reproductive fronds. Others may have entirely fertile fronds, with sori in soldierly alignment along the pinnae or appear only on part of the pinnae or splashed across pinnae in an indiscernable pattern.
Sori may appear as small raised dots, kidney shapes, or, in the case of maidenhair ferns, as crescent shapes at the tips of pinnae beneath the frond. Some examples of sori structures and diverse presentations:
Other information to consider when identifying:
- Form: are fronds clustered or single, rhizomous or colonizing, sturdily vase-shaped or emerging from the ground like errant cowlicks?
- Is the stipe hairy, sticky, smooth, covered in fibers, delicate, scaly, grooved?
- Texture: ‘Finely-cut’ is useful terminology, describing fronds with fractal-like layering of multiples of pinnae and lobes, compared to coarser, more simplistic structures (which could also be described as shapes that are ‘stronger’ or bolder’) and playing those two elements against each other is great way to explore creative ways of combining ferns.
Last but not least, the branching patterns of pinnae.
Simple – fronds are not divided but appear as single leaves emerging from the ground, as in the leaves of daffodils.
Pinnatifid: A blade which is fully lobed, but not fully cut to the rachis (stem). Pinnae appear as undulating structures.
Pinnate: Pinnae are not divided but appear as single lobes.
Pinnate-Pinnatifid: Pinnules are not fully cut through to the costa.
Bipinnate: Pinnae divided twice (Maidenhair ferns, Japanese Painted Fern)
Bipinnate – Pinnatifid: Bipinnate, but not fully divided to the costa.
Tripinnate – Pinnae divided three times