Diderma sp. (D. montanum ?)

Not technically fungi, but often lumped together with fungi
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MaxRum
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Diderma sp. (D. montanum ?)

Post by MaxRum » Sat Nov 19, 2016 6:21 pm

Hi, I am working on the ID of a myxomycete from Malta (growing on a dead stalk possible of a grass), which I have narrowed down to a Diderma for its peridium made of amorphous lime granules. However further ID to species level is not concrete.

According to my observations, the species has a reddish brown stipe (darker at the base), thin peridium with random dehiscence, amorphous, lack a columella (prone to correction), capillitium numerous, white-hyaline, ribbon or strap shaped, 4-8um wide, smooth, spores minutely verricose (observed as rough cloudy surface), 9-11um, dark iodine-brown.

Two things I cannot determine:
1. The complete surety that there is no columella
2. If the peridium is one or two layers

Under a stereomicroscope, i've force-opened some sporocarps and I could not see any solid columella structure, unless it was very short. Could you please guide how this is best detected? Secondly, and on the same line, I could not be sure if there are two layers in the peridium. In cotton blue with lactic acid, the lime coating dissolves leaving a hypothetical film-like coating, while in Congo Red, there are somescale-like patches which I though that both correspond to the second layer.

Capillitium unbranched, smooth, curved but some keys make reference to lime deposits which in my opinion I could not detect anythiing distinct.

Your help is apprecaieted.

Thanks
Attachments
IMG_7178.JPG
IMG_7178s.jpg
IMG_7579.JPG
0.1mm / div (total length 0.5mm c.)
IMG_7590.JPG
Capillitium, ribbon-shaped, 5-8um wide, hyaline
IMG_7595s.jpg
Amorphous lime peridium in congo red
IMG_7614s.jpg
Capillitium in cotton blue+lactic acid (membranous layer of peridium at top?)

MaxRum
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Re: Diderma sp. (D. montanum ?)

Post by MaxRum » Sat Nov 19, 2016 6:31 pm

More photos

So I have narrowed this down to D. montanum v. album, but this is reported with a lighter-coloured stripe and a small columella (which maybe I missed). M. hemisphaericum has discoid sporocarps and distinct columella. D. spumaroides has crystallized lime while D. carneum and D. umbillactum are larger although the latter has a brown stipe but then a distinct columella. D. cinereum should be sessile.

Have I got someting wrong, is the genus Diderma good?
Attachments
IMG_7615.JPG
Columella absent?
IMG_7619.JPG
Columella absent? Stipe distinct, amber-brown.
IMG_7630.JPG
Scaly patches (are they fragments of the 2nd layer of peridium?
IMG_7632.JPG
Sporocarp forced open - Columella ?

Pitufo
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Re: Diderma sp. (D. montanum ?)

Post by Pitufo » Sat Nov 19, 2016 7:29 pm

Hi Max

In your last photo showing the opened sporangia, I think I can see white "veins" running through the dark mass or spores. It is hard to tell but do you think those could be lime nodes? Once you transfer capillitium to water on a slide the nodes are often very hard to see and sometimes seem to vanish as if by magic.

If they are lime nodes, you may want to have a look in the Physarales. Your photos and description are not unlike Physarum pusillum. However the threads of capillitium you show are more in keeping with Diderma, so I could be completely wrong. Apologies in advance if I throw you off the scent.
Two things I cannot determine:
1. The complete surety that there is no columella
2. If the peridium is one or two layers
These are always difficult characters to determine. In my experience, "columella hunting" is best done by very carefully dismantling a sporangia (or several) with very fine needles under the best stereomicroscope you can get your hands on. There may well be better ways.

I am still looking for a good answer to the "one or two layers question" myself as I have been fooled on more than one occasion.

Kind regards,

John

MaxRum
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Re: Diderma sp. (D. montanum ?)

Post by MaxRum » Sat Nov 19, 2016 9:11 pm

Hi John,

Thank you so much for your message which is really appreciated and important. I've rechecked my work and I've assessed an important character wrongs within Physarales, exactly whether the capillitium is calcareous or not. I've always examined this in water or stain mounted on a slide, and as from the photos, they appear hyaline, hence leading to Didermaceae, but following your advice, I've examined the sporocarp in situ and the white thread were visible.

So to confirm lime, the best way to do, hopefully helping other students like me, is to immerse a needle in lactic acid (mine is about 20%) and touch the suspending droplet on forced-open sporocarp, hence distributing the acid on the capillitium. Their disappearance and formation of CO2 bubbles will confirm the limy threads. This happened in my specimen, so voila - its a Physaraceae.

P. pusillum seems to fit the bill, but I have to run again through the keys.

Re columella you are right, needs lots of practice, while re double layer of Didermas, I try to make some more research, but perhaps dissolving the calcareous outer layer with acid and view immediately under light microscope might help to observe the thin, hyaline layer.


Thanks John!
Attachments
CalcareousCapillitium.jpg
Capillitum reacting and dissolving in lactic acid with formation of CO2
IMG_7649.JPG
Calcareous capillitium

MaxRum
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Re: Diderma sp. (D. montanum ?)

Post by MaxRum » Sat Nov 19, 2016 9:29 pm

I'm undecided between Physarum pumillum and P. robustum. The habit of the specimen matches better to P. pumillum, but this is described to have "angular lime nodes". A cursury check on google images and the habitat favours P. pusillum.

MaxRum
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Re: Diderma sp. (D. montanum ?)

Post by MaxRum » Sun Nov 20, 2016 5:45 am

Finally I decided on Physarum pumillum :mrgreen:

Pitufo
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Re: Diderma sp. (D. montanum ?)

Post by Pitufo » Sun Nov 20, 2016 10:34 am

Max, thank you for the tip and photos of lactic acid to confirm the presence of lime. I will give it a try one day.

Lime nodes are very easy to miss in water - I have heaped great quantities of capillitium containing visible lime nodes on to a slide and then added water to look at them under high power and barely been able to find one or two.. Maybe it would be better to try and look at them under hight power without water (?).

Your photos of the capillitium showing lime and CO2 production seem conclusive, well done. I'm just happy I didn't send you down the wrong path :)

Kind regards,

John

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