Greenish crustose lichen on hawthorn twig. Two small areas with apothecia - pale margin, buff centres. Pinhead is approx 3mm diameter. Edit: Possibly Lecanora dispersa?
Caution: Do NOT use iSpot to identify fungi to eat!
Some fungi are very poisonous so a mistaken ID could have serious consequences.
No interactions present.
I have added agreement as to the genus. It might be L. hagenii, though this usually has more greyish margins to the apothecia.
It could also be L. chlarotera - very common on hawthorn and other trees, though it doesn't look quite right for this.
Microscopic examination is necessary.
I wondered about those two as well and discarded them for similar reasons then found a similar-looking L dispersa on your website.
L. dispersa is recorded from trees, but authentically only when there is dust deposition. It would be extremely unlikely to occur on a hawthorn twig under normal circumstances. It is a species of kerbstones, concrete and stonework.
Also, a feature of L. dispersa is that it has little or no visible thallus - the thallus usually being immersed in the substrate, or, if visible, consisting of scattered granules. The effect is of scattered apothecia on the stone surface (hence 'dispersa', I assume). In your photograph there is a well developed crustose thallus. Oddly it is green, but this is either damp or from surface algae.
I still think this is most likely L. hagenii. Your useful scale confirms this is a tiny thallus (so excellent photograph!), and the clustering of the apothecia matches this species. The young apothecia of L. hagenii have pruinose margins, and it may well be that in your photographed material, this pruina has persisted to make the margins whiter than usual. However, I am cautious with anything that is not an exact fit, as there are several other species in this group (Dobson has only a selection).
I can confirm that it's not damp: the twig has been on my desk for a couple of weeks .. and I keep on finding new things on it! It certainly looks as though there is widespread algal growth on the twig.
Many thanks for your help.
Yes, a good twig can provide days of delight. A student asked me what I did for a recent holiday break, and to her amusement/mystification I told her I spent the holiday looking at a twig.
But it gave me three new county records and some other good records, including L. hagenii.
Lat/Lng: 55.4735, -3.2009
OS grid ref: NT241206