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Cladonia macilenta or polydactyla

Posted: Tue Feb 05, 2019 4:34 pm
by CJohnsonOHBR
I always have trouble trying to distinguish Cladonia macilenta from polydactyla, when the podetia on polydactyla are under-developed and the apothecia on macilenta are similarly poorly developed. This is not helped by variations in the descriptions of the soredia on the podetia.
Dobson describes macilenta as "lower part sometimes squamulose, upper part granular or farinose-sorediate, and polydactyla as lower part squamulose and farinose-sorediate above.
Nordic Lichen Flora describes macilenta as ecorticate, abundantly farinose sorediate, and polydactyla as surface of podetia granulose sorediate.
Various websites will have descriptions which will vary between the two or describe either species as farinose- to coarsely granular-sorediate and mixed with squamules.
Some authors also suggest that a K+ purple reaction at the base of the basal squamules is characteristic of polydactyla.

This would tend to suggest that both species are highly variable. So is it possible to differentiate the species when the podetia are not fully developed?

As a novice, I usually spend hours trying to decide and the fail to make a decision. However today I perserved and I'd decided that I had polydactyla or was it macilenta?
K+ yellow, P+ orange, UV-. Apothecia undeveloped, but some red visible on the tips of the podetia. Base of basal squamules white, K-. The podetia were unbranched, slightly tapering towards the tip. Growing on old tree stump, Stornoway, Isle of Lewis.

I'd appreciate an opinion.

Thank you
Christine

Re: Cladonia macilenta or polydactyla

Posted: Tue Feb 05, 2019 5:18 pm
by JennyS
Hi Christine -they look like the sort of Cladonia I'd avert my eyes from and try and find more mature specimens!

Alan Silverside said when testing for a K reaction it is best to test the lower portion of the podetia as apothecia and pycnidia of all red-fruited Cladonia species give K+ red to purple and the underside of their basal squamules also gives a general K+ reaction.

Re: Cladonia macilenta or polydactyla

Posted: Tue Feb 05, 2019 5:26 pm
by Neil Sanderson
Christine

Those are very small young podetia, so the best response is to find some nearby older ones!

To answer some of your questions, I would say Cladonia polydactyla is very variable but Cladonia macilenta not so much (and the later is not closely related to Cladonia polydactyla, but is close to Cladonia floerkeana). The description in Dobson is wrong in my opinion, well developed Cladonia polydactyla is never farinose-sorediate and, as the Nordic Flora states, it is granulose sorediate; that is actually the main way of telling them apart when Cladonia polydactyla is poorly developed and lacks cups. As a general rule if an earlier source differs from the Nordic Flora, the latter is probably correct. The orange patches reacting K + purple on the undersides of the squamules being diagnostic is interesting, but I think this also occurs in other red apothecia Cladonia species such as C. digitata, but I will have a look on Cladonia macilenta. I have attached a couple of picture of well grown material of both species. Cladonia macilenta, is quite a distinct gracile narrow tapering species and is much less widespread than Cladonia polydactyla, at least in the south.

As for your Cladonia: the soredia look too fine to be Cladonia polydactyla and it does not seem to have the normal blueish tinge of this species, so may be young Cladonia macilenta

I hope this helps

Neil

Re: Cladonia macilenta or polydactyla

Posted: Wed Feb 06, 2019 10:58 am
by CJohnsonOHBR
Thank you Neil and Jenny for the very helpful expert advice, which is greatly appreciated.

You are right about ignoring immature Cladonia but as the woodland in Stornoway is the only opportunity we get to look at lichens and fungi in this type of habitat we tend to make the most of our visits and I was unable to resist having a go.

According to NBN Atlas, polydactyla is recorded more frequently than macilenta in VC110. Of course this may be due to recording bias/mis-identification/island effects etc., so it is worth the effort to keep looking, although for a while I think I'll stick to well developed specimens.

I find the keys in NL Flora very useful and it is encouraging to have the endorsement.


Christine