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Possible Verrucaria romeana

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  • November 10, 2025 at 9:34 am #33108
    SylviaD
    Participant

      Hi,

      I wondered if anyone can give some help with this Verrucaria found on the mortar of a churchyard boundary wall in a very damp shaded area among moss. I was considering Verrucaria romeana based on the following:

      Black basal layer

      Very squamulose overlapping nature of the aeroles

      Size of spores – 22.5-27.5 um X 10-13 um

      Well-developed involucrellum

      Somewhere I have read that V romeana, when well developed, has those raised/blasidiate? edges that are present, but I can’t seem to find that information at the moment.

      Any help much appreciated

      Thank you

      Sylvia

      November 10, 2025 at 10:44 am #46739
      Paul Cannon
      Participant

        Hi Sylvia

        I was shown a thallus of V. romeana at Juniper Hall that looks almost identical to your images (see attached), the blastidia aren’t referred to much and seem to be variable in their expression. V. macrostoma can also produce similar structures (see http://www.afl-lichenologie.fr/Photos_AFL/Photos_AFL_V/Texte_V/Verrucaria_macrostoma.htm), the thallus is primarily areolate rather than squamulose but they do intergrade.

        It seems that the gold standard to differentiate the species is that in V. romeana the epinecral layer is absent or poorly developed, while in V. macrostoma it is well-developed; that may be expressed by thalli with an epinecral layer being glossier than those without, but I don’t know how reliable that distinction is. Thin sections of the thallus are really needed. Two sections from Mark Powell are attached, which gives you some idea of what is expected.

        PB030258a.jpg

        [attachment=2]PB030258a.jpg[/attachment]

        Verrucaria squam3929i.jpg

        [attachment=1]Verrucaria squam3929i.jpg[/attachment] squamulosa

        Verrucaria macr4188h.jpg

        [attachment=0]Verrucaria macr4188h.jpg[/attachment] macrostoma

        It’s not easy, but hopefully this helps

        Paul

        November 10, 2025 at 12:54 pm #46740
        SylviaD
        Participant

          Thanks Paul,

          My photos do look identical to your photo. But I will get sectioning and see if I can get some measurements for the epinecral layer or better still not find it much at all.

          Thanks for your help.

          Sylvia

          December 15, 2025 at 7:34 pm #46741
          SylviaD
          Participant

            Hi Paul,

            I had to go back and get some more sample of the potential V romeana, hence the delay, and I have also found a thallus at another church, which seems to be a possible V romeana (keys out in LGBI3). I’ve attached photos below of the epinecral layer from both samples – both have epinecral layers that are at the thickest 9 micrometers and in many places absent. This seems to fit the bill for V romeana, rather than V. macrostoma.

            Thanks,

            Sylvia

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