tiny lichen on Elder - Dimerella?

[Chris Yeates]

hello all


this was discovered on a decorticated attached Sambucus branch at around head height; at first I didn't think of a lichenised fungus and was struck by the deep green colour of the apothecia

under the microscope the abundance of algal cells clearly showed that they were what was causing the vivid green; when dry the difference in colour was striking; I lay no claim to much knowledge of lichens but the apothecia reminded me of a Dimerella which I was shown decades ago while out with Albert Henderson near Leeds; Ursula Duncan's book suggested that Trentepohlia was the supposed photobiont for that genus and so I immediately thought "that can't be it" - however reading Trentepohlia (images of British biodiversity) put me straight on that one

the spores seem to fit well with Dimerella pineti, but nowhere have I come across the mention of the huge difference in colour between sodden and dry apothecia - perhaps this is a commonplace occurrence, not worth mentioning . . . I may of course be way off the mark with this tentative ID

the micro shots are all taken from rehydrated material mounted in water only - the "squash" rather obligingly produced nice sections which show algal cells along the base of the apothecia and also in the subhymenium - clearly creating the bright green colouration

any suggestions gratefully received - thanks in advance

Chris

[diggleken]

Originally Posted by Chris Yeates

hello all


this was discovered on a decorticated attached Sambucus branch at around head height; at first I didn't think of a lichenised fungus and was struck by the deep green colour of the apothecia

under the microscope the abundance of algal cells clearly showed that they were what was causing the vivid green; when dry the difference in colour was striking; I lay no claim to much knowledge of lichens but the apothecia reminded me of a Dimerella which I was shown decades ago while out with Albert Henderson near Leeds; Ursula Duncan's book suggested that Trentepohlia was the supposed photobiont for that genus and so I immediately thought "that can't be it" - however reading Trentepohlia (images of British biodiversity) put me straight on that one

the spores seem to fit well with Dimerella pineti, but nowhere have I come across the mention of the huge difference in colour between sodden and dry apothecia - perhaps this is a commonplace occurrence, not worth mentioning . . . I may of course be way off the mark with this tentative ID

the micro shots are all taken from rehydrated material mounted in water only - the "squash" rather obligingly produced nice sections which show algal cells along the base of the apothecia and also in the subhymenium - clearly creating the bright green colouration

any suggestions gratefully received - thanks in advance

Chris

Hi Chris,
well, apothecia size is right and this is with a green algae which is more noticeable when rusty, but that doesnt explain the colour change in your pics.
There is often a change when wet in these things though as you know. But:
Dobson mentions pieti as being similar to D lutea, which is larger.
He says there is a difference in apothecia when wet for them both, 'tinned apricots when wet and poached egg when dry' so perhaps not your suggestion as that isnt the case here.
Sorry not to help more, thought this may help a bit if you havent Dobson................but you will, I guess, but may have missed that description!
Need Alan?
Cheers
Ken

[poschiavanus]

Originally Posted by Chris Yeates

...

the spores seem to fit well with Dimerella pineti, but nowhere have I come across the mention of the huge difference in colour between sodden and dry apothecia - perhaps this is a commonplace occurrence, not worth mentioning . . . I may of course be way off the mark with this tentative ID

...

Chris

This phenomenon isn't mentioned in literature available to me, but JennyS' description with her pictures of D. lutea mentions:

Apothecia yellow-orange with paler margins, can appear +/- translucent in very wet conditions, possibly seasonal.

Lichens of North America has a couple of other things which may be useful:

D. species can look like Biatora, Bacidia, or Cliostomum, but these all have club-shaped asci with conspicuously thickened K/I+ blue tips.

(D. lutea) Thallus membranous, greenish grey. Apothecia flat to slightly convex, 0.3-1.5(-2.0) mm in diameter, pale orange with a slightly paler margin that is barely or not at all higher than the disk; paraphyses distinctly septate when stained with IKI; spores ellipsoid 7-12 x 2.3.5 um; conidia 3-5 um long, ellipsoid. Habitat: On shaded mossy bark or rocks, often growing over moss. Comments: When immature, the apothecia of D. lutea can resemble those of D. pineti. The apothecia of D. pineti are smaller (0.2-0.4 mm in diameter) and noticeably concave, the disks often have a pinkish tint, and the spores are longer (9-14 x 2-3.5 um).

My copy of Dobson (5th ed.) shows the ascus as being somewhat club-shaped, but LoNA describes them as thin-walled, slender, cylindrical, not-thickened at the tip.

Most accounts I've looked at emphasise the difference in size and colour of dry apothecia, with pineti being described as having a pinkish tinge, whereas apricot seems to be the widely-used as a descriptive term for lutea. However, things aren't helped by the two species being synonymised in quite a few recent continental accounts (e.g., Lichens of BE/LU, Ulirch Kirschbaum's Flectenbilder). This synonymy seems to be an error (see a PDF of a paper on the Genus Dimerella in Slovakia).

Posch

[AlanS]

I have been looking into this myself as while the apothecia in 'normal' condition look just like Dimerella pineti, and the spores match in size and shape, I have also been troubled on two counts:

a) the colour of the soaked apothecia in a species that does have Trentepohlia as its photobiont

b) the substrate, which seems a bit nutrient rich for D. pineti.

I have been trying very hard to make it a species of Absconditella, a genus with a chlorococcoid photobiont. However, nothing fits. A. delutula is not too far away, but that has wider spores, and the photograph in Skyddsvardar lavar ... suggests more delicate apothecia.

Posch has done valuable research that settles the ascus shape, and the worrying drawing in ed. 5 of Dobson is no longer present in ed. 6. I was going to look, myself, at ascus shapes in material in both species but mundane things like student essays have taken higher priority, so I am abandoning that. Maybe I'll do so before putting both species up on my website.

Lichens with chlorococcoid algae do often go completely green, apothecia included, when soaking wet, and while books may not mention this, it is not unusual. Lecania species, which are frequent on elder and have small, soft apothecia, do this and I did wonder about the soaked specimens, but they have the thick margins of D. pineti so no mix up there. I can only conclude that the Trentepohlia has not developed its orange pigment, which is sometimes the case. Maybe a shade effect? Maybe I should just try soaking D. pineti to see what it does myself, but I am a bit reluctant when I only have one small sample.

So yes, non-soaked material looks like D. pineti, it matches D. pineti microscopically, and there doesn't appear to be any alternative. I think the identification is safe.

Incidentally, I cannot find that D. pineti and D. lutea have been synonymised in the two websites that Posch mentions. It would be surprising if they were.

Alan

[Chris Yeates]

Originally Posted by AlanS

. . . . . Lichens with chlorococcoid algae do often go completely green, apothecia included, when soaking wet, and while books may not mention this, it is not unusual. Lecania species, which are frequent on elder and have small, soft apothecia, do this and I did wonder about the soaked specimens, but they have the thick margins of D. pineti so no mix up there. I can only conclude that the Trentepohlia has not developed its orange pigment, which is sometimes the case. Maybe a shade effect? Maybe I should just try soaking D. pineti to see what it does myself, but I am a bit reluctant when I only have one small sample.

So yes, non-soaked material looks like D. pineti, it matches D. pineti microscopically, and there doesn't appear to be any alternative. I think the identification is safe. . . . .
Alan

Many thanks for that Alan; I don't feel so bad about being rather nonplussed myself now; I could send you the material if it would help

cheers

Chris