Thursday, September 5, 2013

Clinton's Wood Fern (Dryopteris clintoniana). Or not?

Note ~ More research and time in the field has revealed new information since this was originally posted. There are several not uncommon Dryopteris hybrids that are a real cross (pun intended) to distinguish from one another. Boott's Wood Fern (Dryopteris × boottii) is a hybrid between the Crested Wood Fern (Dryopteris cristata) and the Evergreen Wood Fern (Dryopteris intermedia) and also has angled, louver-like pinnae. The Triploid Wood Fern (Dryopteris × triploidea) is a hybrid between the Spinulose Wood Fern (Dryopteris carthusiana) and the Evergreen Wood Fern (Dryopteris intermedia), exhibits characteristics of both parents (and the fern in the photos below), and can be difficult to separate. So – the fern featured below might in fact be one of these hybrids, not a Clinton's Wood Fern ...

An uncommon inhabitatant of wet woodlands, Clinton's Wood Fern is a natural fertile hybrid between two other Dryopteris species, the Crested Wood Fern (Dryopteris cristata) and Goldie's Fern (Dryopteris goldiana). The fronds arise from the rhizome in a circular pattern.

The fertile fronds are larger and more erect than the sterile fronds. The fertile fronds, two of which can be seen on the far side of the plant from the perspective of the following photo, also exhibit another characteristic typical of Clinton's Wood Fern.

A closer look at the fertile fronds in question – note how the pinnae are relatively widely spaced, and moreover they are twisted or tilted out of the plane of the blade. The only other local fern with this feature is the Crested Wood Fern (Dryopteris cristata), and its pinnae are turned even more markedly, almost at a right angle to the plane of the blade and nearly horizontally with respect to the ground.

A fertile blade as seen from above. The sides of the blade are parallel for much of its length, with the basal pinnae being distinctly shorter and more triangular than the remaining pinnae.

A triangular basal pinna.

The pinnules are deeply lobed and bristle-tipped.

A closeup shot of the rachis ...

... and the scaly stipe.

The sori are positioned about half-way between the midvein and the margin.