A recent molecular project looking at species boundaries between two British Grimmia species, Grimmia donniana and Grimmia arenaria, with Dr Des Callaghan reminded me that there were still some unedited nuclear ribosomal Internal Transcribed Spacer ITS2 sequence files for the genus from Dr Wolfgang Hofbauer’s EU-SYNTHESYS-funded visit to RBGE back in 2014. At that point we had been looking into mosses that grow on building surfaces, and had ended up focusing on another genus, Schistidium, instead of Grimmia. This new project seemed like the ideal opportunity to dig out and utilize the older unused files.

However, having unearthed and edited the 2014 Grimmia sequence files, I discovered that the genetic variation between them and the species that we are currently working on is too high to make useful comparisions. The 19 sequences from 2014 were also not an exact match to any identified plants in the NCBI database, GenBank. The closest match for many of them was an environmental sample, accession KM515068, that had been sequenced from an air sample by a lab in Germany. The closest matches for others were three Grimmia pulvinata sequences from California.

Grimmia pulvinata – photograph by Gordon Ruthero from Mosses and Liverworts of Britain and Ireland – a field guide. (c) British Bryological Society (2010)

Pulling the four relevant sequences from GenBank and adding them to the sequences generated at RBGE showed that there is quite a lot of genetic variation between these accessions. In the phylogram below, specimens identified as “cf pulvinata” were lacking mature sporophytes. When the substrate a plant was growing on is known, it is given (ETICS stands for External Thermal Insulation Composite System). Parsimony bootstrap values are given on a few of the branches; however, the sequences tend to only differ by one or two base pairs and one or two gaps, meaning that statistical support for groupings is not going to be high.

Maximum parsimony ITS phylogram

Because ITS2 is a non-coding region of DNA, in addition to variation in nucleotide sequences between accessions (which is visible in the phylogram shown) there are also gaps (insertions and deletions) in the sequences that do not show up in this analysis. For example, the four accessions from Germany and Austria that have 66% parsimony bootstrap support (a statistical support measure for groupings of taxa, obtained through random resampling of proportions of the original DNA sequence data) in the phylogram also share a unique two base pair deletion.

This analysis shows that there are several genetically distinct lineages within the morphological species Grimmia pulvinata – within ten German accessions there are six different DNA sequences, while we have three different DNA sequences within six Scottish accessions.

Intriguingly, there is a small lineage coutaining four accessions, two from Germany and two from Scotland (from the coastal Borders town of St Abbs – or New Asgard, as Avengers fans may better know it, and the Pentland hills near Edinburgh), that were all collected on rocks as opposed to on manmade surfaces.

Without far more thorough sampling, both in terms of accessions of plants and quantities of genetic data, it is only possible to speculate, but it may well be that different lineages within Grimmia pulvinata correlate with some of the distinct substrates that the species is known from.

Even with a plant as common, and as commonly overlooked, as this pollution-tolerant urban bryophyte, there is still genetic diversity to explore and explain.


Voucher and collection information for new RBGE Grimmia pulvinata and Grimmia cf pulvinata sequences

RBGE DNA no.VoucherLocationDateNotes
14-0036705Hofbauer 174Scotland, Edinburgh, RBGE11/09/2014concrete wall
14-0036706Hofbauer 173Scotland, Edinburgh, Ferry Road12/09/2014cement of stone wall
14-0036707Hofbauer 163Italy, Triest, near Grotta Gigante01/06/2014concrete
14-0036708Hofbauer 121Germany, Valley, Bavaria29/08/2014no sporophytes; concrete
14-0036709Hofbauer 116Germany, Valley, Bavaria29/08/2014concrete
14-0036710Hofbauer 094Germany, Valley, Bavaria29/08/2014concrete
14-0036711Hofbauer 084Germany, Valley, Bavaria29/08/2014 tiny, no sporophytes; ETICS
14-0036712Hofbauer 073Germany, Valley, Bavaria29/08/2014 tiny, no sporophytes; ETICS
14-0036721Hofbauer 110Germany, Valley, Bavaria29/08/2014no sporophytes; rock
14-0036722Hofbauer 106Germany, Valley, Bavaria29/08/2014rock
14-0036723Hofbauer 103Germany, Valley, Bavaria29/08/2014no sporophytes;  rock
14-0036724Hofbauer 069Germany, Valley, Bavaria26/08/2014no sporophytes; ETICS
14-0036725Hofbauer 062Germany, Valley, Bavaria26/08/2014no sporophytes; ETICS
14-0036726Hofbauer 009Austria, Kufstein, Tirol17/08/2014concrete
14-0036727Hofbauer 006Austria, Kufstein, Tirol17/08/2014concrete
14-0036732Kungu S277Scotland, Dumfries & Galloway, Eliock Wood24/10/2003top of sandstone bridge parapet
14-0036733Long 36320Scotland, Berwickshire, St. Abbs29/09/2006rocks
14-0036734Long 31186Scotland, Lauder Burn28/05/2002old limy wall
14-0036736Long, Chamberlain, Flagmeier 36630Scotland, Pentland Hills04/04/2007rocks