Arthonia hypobela? in the New Forest

I have been finding some interesting stuff since I started looked at twigs harder in the New Forest and have been meaning to do some posts on the result. This one has just come up and is so surprising that it has prompted me to start with this.

I have been aware, sort of in the corner of my eye, of very silvery patches of bark with irregularly rounded Arthonia like apothecia. It is uncommon and when I collected it earlier the specimen I took had no spores but did have broadly clavate asci, a granular brown-black K+ greener epithecium and no apothecium margin.

I found some more recently and this time it had spores, and these were mult-septate and quite large which seemed to instantly rule out any known British Arthoniaceae. The details are:

Fallen twig in by road in Beech – Oak pasture woodland, Nicholas Corner, Bartley, New Forest

Thallus marked by a silvery area of bark, not lichenised; apothecia irregularly rounded 0.25-0.50 mmm across, 100 µm high; ascomatal gel I+ red; epithecium brown-black, with granules, somewhat K+ greener; hymenium colourless; hypothecium thin and pale brown; asci broadly clavate, with a large apical dome, and an ocular chamber, up to 50 x 30 µm; spores (4–) 6 – 8 septate more rounded at one end and more tapered at the other, (20–) 30 – 35 (6–) x 9 – 11 µm () = measurements from immature(?) spores.

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Thallus & apothecia

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Apothecia cross sections

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Spores & acsci

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Ascus in K/I

This was clearly not in LGBI3, the spores were unlike any British Arthoniaceae, so I ran it through the Arthonioid key in Italic 8 https://italic.units.it/flora/index.php?procedure=ext_key_home&key_id=2731” class=”bbcode_url”>https://italic.units.it/flora/index.php?procedure=ext_key_home&key_id=2731. This came out at Arthonia hypobela https://italic.units.it/index.php?procedure=taxonpage&num=139” class=”bbcode_url”>https://italic.units.it/index.php?procedure=taxonpage&num=139. This was quite a good match except they had narrower spores at 30-38 x 4-5 µm. They noted it as “ a rather poorly known, probably western species growing on acid bark, including that of conifers; the Italian material was collected on Quercus pubescens and Q. suber.”

The species is more commonly collected in eastern North America and is also described here https://lichenportal.org/portal/taxa/index.php?tid=52439” class=”bbcode_url”>https://lichenportal.org/portal/taxa/index.php?tid=52439. This gives the spore size as 3-8-septate, 21-42 x 3-6 μm. However, the where the details of the scanned specimens below give spore sizes these had spore widths that ranged 11 – 18 µm, which is a disconnect from the description. Some of these had spore drawings and showed spores with big end cells so might actually be Arthonia ilicina. However, two at least have sketches of similar spores to my specimen, so some American collections under the name Arthonia hypobela do match my specimen.

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One of the specimens

An issue might be that my specimen was producing smaller spores that appeared to be immature spores, that were a better fit with the descriptions. Anyway it looks like Arthonia hypobela is an OK name until someone does some further work on these. The New Forest taxa seems likely to be closely related to Arthonia hypobela at the least, even if it is not it.

Neil