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Bacidia squamellosa with Pycnidia

Posted: Thu Jan 10, 2019 9:27 pm
by Neil Sanderson
All

One nice find from the Wessex lichen Group’s New Year meeting to the upper end of Stricknage Wood, New Forest, was Bacidia squamellosa with pycnidia. I find this species rather difficult to pick out in the field. The coralloid dissected thallus are very like Micarea prasina s. lat. in the field. Most Micarea prasina s. lat. has a grey-green colour that is quite different but there are also yellow-green morphs that are maddeningly similar. The algae are very different, however, the Bacidia algae cells are up to 12 µm diameter while those of Micarea are a maximum of 8 µm diameter. Near the end of the day I spotted some potential Bacidia squamellosa on an old Sallow, so I bagged it. Back home the algae matched Bacidia squamellosa but I also spotted some small very pale pinkish-brown 0.25mm diameter marginless disks, which was odd. Sectioning one it turned out to be a pycnidia with conidia 40 – 50 x 1 µm. Fortunately this matched the description of Bacidia squamellosa pycnidia in https://www.researchgate.net/publicatio ... th_America.

The LGBI says pycnidia have not been recorded from Britain. Has anyone else seen these?

Re: Bacidia squamellosa with Pycnidia

Posted: Fri Jan 11, 2019 8:39 am
by Chris Johnson
Hello Neil, welcome to the forum. It would be good if more lichenologists used this site.

I'm too much of a novice to make any helpful comments but finding the picnidia is a triumph. One point that does intrigue me is the precise size-range of the photobiont between the two species. By far the commonest Trebouxioid photobiont of lichens is Trebouxia arboricola which has a cell-size range of 2–25 µm. So, is the photobiont of Micarea a different species or has the fungal partner some influence over cell-size?

Regards, Chris

Re: Bacidia squamellosa with Pycnidia

Posted: Fri Jan 11, 2019 9:46 am
by Neil Sanderson
Chris

Thanks

The Lichens of Great Britain and Ireland (LGBI) gives the range for Micarea prasina as 4-7 μm and for Bacidia squamellosa 5-12 μm, so it is finding larger diameter algae that clinches in identification. Micarea algae are distinctively small, to quote the LGBI:
Photobiont green, cells usually thin-walled, c. 4-7 μm diam. and often paired (‘micareoid’)
Although it is not quite that simple, a few species including Micarea sylvicola and Micarea bauschiana have chlorococcoid, non-micareoid photobionts, but recent DNA sequence analysis has put then in a different genus Brianaria and family Psoraceae https://www.researchgate.net/publicatio ... cola_group. The ‘micareoid’ algae containing 'Micarea' are all in the Pilocarpaceae (along with species without ‘micareoid’ algae) https://pdfs.semanticscholar.org/6fcc/a ... a17ec5.pdf but are being split up into different genera (More new names oh joy).

Exactly what the ‘micareoid’ algae are classified as I have no idea from a quick google, the inverted comas are suggestive of taxonomic mystery.

All the best

Neil

Re: Bacidia squamellosa with Pycnidia

Posted: Fri Jan 11, 2019 12:07 pm
by Chris Johnson
Neil

Thanks for that.

I think micareoid algae mainly refer to the genus Elliptochloris, but may also include Pseudochlorella.

Regards, Chris

Re: Bacidia squamellosa with Pycnidia

Posted: Fri Jan 11, 2019 8:20 pm
by JennyS
Good to see you here Neil - and I echo Chris Johnson's comment that it would be great if there were more lichen posts!
Really helpful to see the algae images as that's an aspect of lichen identification I struggle with