Identification notes
Although normally a distinctive species, care needs to be taken, especially after heavy or prolonged rain, to avoid confusion with M. consanguinea. This is because identification relies heavily on the position of the gemmae on the attenuated shoots and such rain can wash many of them off.
This epiphyte is sensitive to air pollution and so it is only found in places where air quality is good and where it is not likely to desiccate. It has returned to many areas where it had declined because of sulphur dioxide pollution. Elder is a particularly favoured host, although it does grow on a range of trees and shrubs.
To identify M. violacea with certainty, you’ll need to see gemmae on the nerve of the end of the thallus as well as on the thallus margins. When well-developed, the clusters of gemmae at the thallus tips look rather lollipop-like. The attenuated thalli of M. consanguinea lack the gemmae on the nerve and those on the margins often descend some way from the tip, making the thalli look broad and flattened at their apices.
Gemmae are normally abundant, but if not, fortunately there are other ways of confirming M. violacea. Firstly, thalli turn a striking pale to dark turquoise blue colour after drying, but this can take weeks or even months to develop. A better, faster method is to examine the nerve of an attenuated branch and count the number of (longitudinal) rows of epidermal cells overlying it (there’s a good photo of this in the gallery below). M. violacea has 3-6 rows, compared to only 2 in M. consanguinea.
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