Is this Polystichum aculeatum?
- Dear friends,
I found a shield fern which I hold for Polystichum aculeatum, however, some details make me wonder whther it might be a garden escape of a diferent species (see photos ).
I found it in the Netherlands. we hardly have a wild population of any Polystichum around here, though the one mentioned above is the least exceptional. hese are the details that made me wonder:
- between the brown, large scales of the stipe there are smaller white, long ciliate, almost stellate, perhaps even peltate scales. I have neve seen any reference to such scales. They don't appear on the aculeatums in my herbarium, but that metrial is not as good as it could have been. My setiferums from Madeira have something similar, though, but they are much more triangular and well-hidden between the more numerous brown scales.
- the base of the pinnulae is not adnate but very shortly stalked. The base of the secundary segments is 90° or slightly less, so neither sharp nor obtuse.
- the basal acroscopic pinnule is not set apart, only slightly larger than the next.
The lamina is not (much) reduced towards the base as it is in P. aculeatum. The plant grows in a dark, moist place and hadn't produced any sori. What do you think of it?
Wim de Winter
- An interesting find, Wim.
Do you have any photos of an entire frond, or the lower few sets of
I personally feel there is sufficient variation in Polystichum
aculeatum and P. setiferum for such characters as the angle within
the pinnules, and the thickness of the pinnule stalks, to be
unreliable on their own for identification. Similarly, fresh fronds
of aculeatum can feel rather soft, while old fronds of setiferum can
be quite thick and stiff.
The above should only be considered after checking the outline of the
base of the frond, which to my mind is a far better way of separating
the two species.
The lower pinnules of aculeatum gradually taper in length down the
rachis, whereas the lowest ones of setiferum remain almost as long as
those of the middle of the frond, there is a distinct "cut-off" point.
If you have an established alien, I would imagine it would be more
likely to be one of the species that are widely available in
horticulture, and therefore more easily recognisable. I know of P.
munitum in Cornwall and Surrey in the UK (where it has hybridised
with P. setiferum in both sites) and P. tsus-simense on a basement
wall in central London, though there may be others.
- Hello Howard,
I have added a photo of the whole plant, but the leaf-bases don't show up very well. I have collected a leaf, but it's still in the press now and it will remain there at least till Sunday.
By the way, re-reading my own observations I wonder why my first idea was aculatum rather than setiferum. Seems to conform better.