The Ferns – an Identification Guide: Part 4 Martin Godfrey
Polystichum setiferum (Martin Godfrey) Fig. 1 Polystichum sori (Martin Godfrey)
Polystichum species We have again had a rather odd year although it has been simpler to get out to more places to see more plants. I have decided to keep this article fairly straightforward and introduce the Shield-ferns, genus Polystichum which, for two of the species, is common but which can be confusing for the novice. Introduction There are three species of Polystichum found in Britain – the common and abundant P. setiferum Soft Shield-fern and P. aculeatum Hard Shield-fern, and the rather rare P. lonchitis Holly-fern. The first two are large and grow in the classic “shuttlecock” form of many ferns, while P. lonchitis is smaller and tends to have a rather untidy growth form amongst the rocks where it usually grows. Because of their growth form and obviously “ferny” appearance, the first two species may be mistaken for Male-ferns, Dryopteris, by the beginner. A good way of telling them apart is to look at the indusia on the underside of the pinnae – in Polystichum they are circular (Fig. 1), while in Dryopteris they are kidney shaped (Fig. 2).
Fig. 2 Dryopteris sori (Martin Godfrey)
Polystichum setiferum This species is common in base-rich woodlands in Shropshire where is can form quite abundant stands. Superficially it looks rather like P. aculeatum, but as mentioned above, the frond has a rather less leathery and stiff feel to it. There are also two good reliable distinguishing features:
All three Polystichum species have fronds with a rather stiff leathery texture and long points on the edges of their pinnae. However, P. setiferum (Soft Shield-fern) is, as its common name suggests, rather less stiff and the points have a less “prickly” feeling. P. setiferum and P. aculeatum both have bipinnate fronds while those of P. lonchitis are once-pinnate.
The first is to look at the base of the frond; the basal pinnae are more or less the same length as those above, giving the frond a truncated look, and below this the stipe is quite long and narrow and not heavily scaly (Fig. 3). The second is to examine the structure of the
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