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Verrucaria from Denmark

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  • March 11, 2021 at 1:31 pm #32060
    JonasRavn

      This specimen was found growing on a fist-sized fragment of concrete lying on the forest floor in a rather closed canopy forest. I have landed somewhere in the “murina-group” and I am having a hard time deciding on the correct ID. I have measured 15 spores, which average to 17.43 x 7 µm – the smallest spores I found were ~15 µm long and the longest; 22 µm. This is within the range of several species, but perhaps too large for V. dolosa (which was my working hypothesis based on morphology. The thallus is very thin, film-like and does not appear completely restricted to the concrete, as it spreads onto larger siliceous pebbles in the matrix. The seemingly bullate structure of the thallus is a consequence of the structure of the concrete – the thallus is filmy throughout. I have attempted to get a complete section of a perithecium, but the very thin thallus makes this a frustratingly difficult task. Any comments or suggestions that can help move me closer to a definite ID are more than welcome.

      Verrucaria sp. #3.jpg

      [attachment=0]Verrucaria sp. #3.jpg[/attachment]

      Verrucaria sp. #3 (målebånd).jpg

      [attachment=1]Verrucaria sp. #3 (målebånd).jpg[/attachment]

      Verrucaria sp. #3 section 1.jpg

      [attachment=8]Verrucaria sp. #3 section 1.jpg[/attachment]

      Verrucaria sp. #3 section 2.jpg

      [attachment=7]Verrucaria sp. #3 section 2.jpg[/attachment]

      Verrucaria sp. #3 section 3.jpg

      [attachment=6]Verrucaria sp. #3 section 3.jpg[/attachment]

      Verrucaria sp. #3 section 4.jpg

      [attachment=5]Verrucaria sp. #3 section 4.jpg[/attachment]

      Verrucaria sp. #3 spores 2.jpg

      [attachment=3]Verrucaria sp. #3 spores 2.jpg[/attachment]

      Verrucaria sp. #3 spores.jpg

      [attachment=2]Verrucaria sp. #3 spores.jpg[/attachment]

      Verrucaria sp. #3 spore (large) 2.jpg

      [attachment=4]Verrucaria sp. #3 spore (large) 2.jpg[/attachment]

      March 12, 2021 at 5:04 pm #44073
      Mark Powell
      Participant

        This might well be one of the bewildering, poorly understood taxa that have features similar to, and often intermediate between, V. dolosa and V. murina. In which case I probably can’t offer much help as I have many of my own collections of such things awaiting identification. It is useful that you mentioned that the thallus morphology is film like and highly affected by the bullate nature of the underlying substratum. I wonder if you have considered V. elaeina which is rather common on fragments of rock, including concrete, in moderately shaded situations close to the ground? I’m afraid that these little Verrucaria specimens are very difficult, often suppressed and/or browsed, and with lots of poorly understood or unknown taxa as possibilities. Sometimes I compare with good material of known species and decide whether it is or isn’t the same thing. Many times I am unable to make a decision. I’m sorry this reply makes it all sound so difficult. If I have any flashes of inspiration I will respond further but for the moment I will leave you with a link where you will find images of V. elaeina: http://fungi.myspecies.info/taxonomy/term/7671/media

        March 15, 2021 at 10:46 am #44074
        JonasRavn

          I suspected that it was not a crystal clear case – it rarely is with Verrucaria spp. in my experience, however limited it still is. Thank you for the link, it is a great site that I have used frequently for the high quality microscopy images of quite a large number of taxa.

          I have considered V. elaeina and it is not a bad fit in terms of spore-size, but I am not sure that the shape of the spores is right. According to LGBI, V. elaeina has ellipsoid spores whereas the spores in my specimen have a +/- distinct taper towards one end and instead appear +/- sole-shaped. This tapering is mentioned for V. dolosa in LGBI, but I am unsure how common this shape is in Verrucaria and if it should be considered as evidence for V. dolosa. What do you think?

          March 15, 2021 at 12:54 pm #44075
          Mark Powell
          Participant

            Unfortunately I can’t answer your question about whether the tapering of the ascospores mentioned for V. dolosa is in any way diagnostic. I am very glad that you have raised the subject though. It is always difficult to know whether such observations have been made in reference to other similar species or whether it is a comment that has been lifted from a previous publication which was only considering the one species. The following website conveniently has micrographs of V. dolosa and V. elaeina ascospores. I am not very familiar with the website but I have no reason to doubt its integrity.

            https://waarneming.nl/taxa/15233/?genus=Verrucaria

            I am not sure that I can detect a great difference in shape but perhaps those of V. dolosa are slightly more tapering. Perhaps this will stimulate me to dig out specimens of both Verrucaria species and look at the ascospores with their shape specifically in mind. I am approaching this with a slight scepticism that the shape of the ascospores in V. dolosa is particularly diagnostic but keeping a very open mind. Even if we aren’t making much progress with identifying your specimen, I am pleased that this discussion is taking place.

            The following micrograph from the lichens maritimes website ( http://www.lichensmaritimes.org/index.php?task=fiche&lichen=1084 ) shows part of the problem with placing too much weight on the shape and size of ascospores. They can be very variable even within a single perithecium. These are ascospores of V. elaeina.

            Screenshot 2021-03-15 at 12.50.35 PM.png

            [attachment=0]Screenshot 2021-03-15 at 12.50.35 PM.png[/attachment]

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