Identification notes
This is arguably our smallest species of Fissidens and although its massed capsules are conspicuous in the winter through to spring, they almost look like they are growing from the ground itself.
It loves clayey ground – the heavier the better – and shade too. Although it is definitely one of the more distinctive of our Fissidens species, it is usually so small that microscopic examination is needed to confirm its diagnostic characters.
The main thing to check first is whether its leaves have a border of narrow, elongated cells. It is one of only two very small Fissidens that grow on soil that lacks such a border; the other is F. celticus, which usually also has a bent nerve. But that species has numerous pairs of leaves whilst another useful field character for F. exilis is that it has very few pairs of leaves. Other very small terricolous Fissidens, such as F. viridulus and F. incurvus, always have at least partially bordered leaves.
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