Black crustose mosaic

[chrisjohnson]

Not quite black dots on rocks as the apothecia are linked. There is no discernable thallus unless it is part of the black structure. Growing on a headstone in a coastal graveyard; the substrate seems to have quartz in it.

I did think it could be described as lirellate and looked at Opegrapha but I am not convinced. Can anyone suggest, at least, a genus?

Thank you, Chris

[synangium]

Conjoined dots on rocks -

Porpidia perhaps? I don't know. The stuff of nightmares!

Nigel

[JennyS]

Hi Chris - wish you had more trees up there to lichen hunt among!

Another 'avert eyes and scuttle past' beastie but you might be in the Lecidea department of black dots.
It seems similar to Dobson's description of Lecidea auriculata agg (2005 edition page 235, better photo than in the 2011 edition) but that is no way a suggested identification!

[chrisjohnson]

Hi Jenny

A few trees would add some diversity but I'll just have to apply myself to granite!

I have the 2005 edition of Dobson which is generally acknowleded as having the best photos so, as I have Smith et al for the more detailed text and up-to-date taxonomy, I won't bother with the 2011 edition.

Lecidea auriculata agg. does read well and the substrate is spot on. I'm going back there this afternoon to revisit some green 'stuff' (yes, hardly scientific), so will collect some more of the Lecidea and see if anything is viable under the microscope.

Thanks for the help.

Chris

[JennyS]

I won't bother with the 2011 edition.

My 2011 edition lives in the car to provide me with a knife carrying alibi

[chrisjohnson]

Originally Posted by JennyS

My 2011 edition lives in the car to provide me with a knife carrying alibi

Perhaps best not to ask what kind of knife you carry around!

Sorry Nigel - I completely missed your suggestion while rushing this morning, however, I think Jenny is a lot closer that she wants to admit to.

Chris

[chrisjohnson]

In a moment of madness I returned to this one today and managed to find a couple of (almost) mature asci. The spores measure 19-21.5 x 8-11µm which would appear to rule out Lecidea.



Chris

[synangium]

Perhaps not Lecidea itself then, but it must be a genus in the so-called Lecidea group. I'm still wondering about Porpidia. Dobson (2011) says a species-level ID is difficult without thin layer chromotography, but your photo, with its less-than-obvious thallus, has some resemblance to P. crustulata in the book and on the British Lichens website, although some images elsewhere look nothing like. Dobson gives spores of 10-17 x 5-9µm (except in the key: "spores 10-17mm long". Yes, millimetres. Wow!) Confusingly, the key says "apothecia separate" for P. crustulata, which doesn't tie in with the photo. Identification is hard enough without the ambiguity.

Anyway, there are other Porpidia sp. that sit more firmly within range of your 19-21.5 x 8-11µm, so they might be worth considering. Then again, since I'm avoiding this whole group for the time being, it might equally be a wild goose chase, but I thought I'd chip in.

It reads like K/I testing of the ascus would help, but that sounds tricky to get right.

I hope you make further progress on this one.


Nigel

[chrisjohnson]

Hi Nigel

I did look at Porpidia when I belatedly saw your thread but was already on the Lecidea route by then, and Dobson's image was very convincing. Your point regarding images is true of so many: what looks convincing in one book is totally differnt in another or on a website. Time of year, weather, age must all be factors.

The site of this lichen isn't far away so I will get some fresh material and try worling through the keys. The only iodine I have is in Melzer's but it should work with K.

Thanks for the encouragement: better to persue one as far as possible rather than have half a dozen maybes (probably end up with one maybe).

Chris

[chrisjohnson]

Hi Nigel

With the remaining bits I managed a more mature ascus with the spores slightly larger: 19-23 x 8-11µm. With the apothecia measuring up to 3mm, the Porpidia key takes me to P. macrocarpa. Not unreasonable, but is it enough?

Chris