Plymouth Phil's picture

Dryopteris aemula, Down Tor, Dartmoor

Observed: 8th June 2008 By: Plymouth PhilPlymouth Phil’s reputation in PlantsPlymouth Phil’s reputation in PlantsPlymouth Phil’s reputation in PlantsPlymouth Phil’s reputation in Plants
D aemula, Down Tor
Down Tor rock crevice in overhang
Description:

Growing in a crevice of a Dartmoor Tor. I find it surprising that this fern survives in such an exposed habitat.

Identifications
Species interactions

No interactions present.

Species with which Broad Buckler-Fern (Dryopteris dilatata) interacts

Comments

Plymouth Phil's picture

Pinnules

These pinnules are concave!!

cicuta58's picture

Pinnules

Concave would mean the rim was higher than the centre which it clearly is not!

cicuta58

Plymouth Phil's picture

Pinnules

To my eye, the pinnules are quite clearly curled inwards so that the rims are higher than the centres. I think it is best to agree to disagree on this one.

landgirl's picture

Confused!

Doesn't it depend on whether you are looking down at the top surface or the underneath of the pinnules? These seem convex if you are looking at the upper side, but become concave if you look at the underside, by my understanding of the terms.

lavateraguy's picture

Indeed it is a problem ...

... that whether a surface is convex or concave depends on which direction that you are looking at it from.

That said, the mature foliage here looks, to my eye, neither convex nor concave. The young foliage is is convex (from above), but that's not unusual for ferns.

landgirl's picture

Yes...

...that's what I thought.

Plymouth Phil's picture

Defining terms

You are right to say that convex and concave depend on your viewpoint. It would be assumed that you are looking at the upper surface of a pinnule from above when you have to decide whether it is convex or concave.

We have to be sure that we agree on the definition of "pinnule" so that we are concentrating our attention on the same part of the fern frond.

Stace says that "pinnule" is a term usually applied only in ferns. It describes the ultimate division of a fern frond.

In the photo of the Dartmoor fern, we are looking at the upper surface of the frond.

I hope this clarifies things a little.

landgirl's picture

Thanks

I've been staring at the photo under the highest magnification for ages, and I'm still not sure. The edges of the pinnules behave like those optical illusion things where you blink and suddenly get a different perspective. I'm sure it's much easier when you have the plant in hand!

Plymouth Phil's picture

Dryopteris dilatata or Dryopteris aemula

" I'm sure it's much easier when you have the plant in hand!"

You are right there! The plant in the photo with the crisped frond was growing alongside many other ferns which were very obviously typical D. dilatata. None of these more typical D. dilatata had crisped fronds.

I think we should draw this debate to a close. I have agreed to disagree with Cicuta58 and I respect his opinion. Perhaps enough has been said.