Zygodon stirtonii

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Identification notes

Even the most experienced bryologists can make mistakes in the field with Zygodons, so don’t feel ashamed to take back a selection of these mosses from trees and walls for microscopic confirmation.  Of course, there are a number of ‘rules of thumb’ which can prove helpful when selecting material:  fruiting plants on trees are often Z. conoideus, the leaves of Z. conoideus are usually straighter than the slightly recurved ones of Z. viridissimus.  On stonework we usually have viridissimus…or do we?

Take a closer look: Z. stirtonii was formerly considered to be just a var. of Z. viridissimus, but the differences from that species, though slight, are sufficiently consistent to merit specific rank. The key differences lie in the shape of the leaf near the tip. In Z. viridissimus, which is the commonest of the species occasionally found on stone, the nerve, though strong below, gives up just as it is about to reach the tip, fizzling out just before the final few cells.  In Z. stirtonii, the nerve actually increases slightly in thickness as it reaches the tip, protruding in a stout mucro.  Furthermore, the leaf tip is asymmetrical – the lamina finishes slightly higher on one side of the leaf compared with the other. These features can be seen through a hand lens with a little practice and with the eye of faith.  However, through bitter experience one learns that the eye of faith can all too readily degenerate into the hand lens of self-deception, so, until you get the hang of it, checking such features under the microscope is a wise strategy.

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Distribution in Great Britain and Ireland

Zygodon stirtonii was not mapped separately in the BBS Atlas 2014, but was included with Z. viridissimus.

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