Tuesday, 3 March 2015

Ctenidium torment

Tom Blockeel just returned a specimen of Ctenidium molluscum that I had collected as var. condensatum from upland crags in Brecks - a dense specimen with some long shoots and orange tinge (and fruiting).  However, Tom didn't think it looked any different to var. molluscum under the microscope (and it didn't have the strongly plicate leaves of true condensatum) - Tom admits that he doesn't really understand var. condensatum and that he also sees similar large forms of C. molluscum with an orange tinge in the uplands.    So what is most of the Ctenidium we see in the uplands - surely not another variety?.   Over the years I have tended to avoid trying to identify Ctenidium to variety as I never felt very confident with them, but weedy looking woodland forms certainly looks very different to these upland plants. When Johnny Turner dropped a specimen of var. robustum he had collected on Mynydd Du on my desk, it at least did look different to other Ctenidium I had seen, although when I looked at a few herbarium specimens from Scotland in NMW, the Carms plant seemed much less robust.  I guess we need to find and encourage an enthusiastic student to do some molecular analysis on this one.


  1. It seems to me that the delimitation and unambiguous recognition of varieties is often problematic in the systematics and taxonomy of both bryophytes and vascular plants. One reason for this is the failure to recognise that many species are capable of large morphological variations (acclimation responses) depending on where they are growing. Is it really surprising that a woodland population of a species looks different to one from the top of a mountain? Unless it can be shown that differences are maintained in reciprocal planting experiments, or there is good genetic evidence for varietal status, and particularly if people keep finding intermediate states (an indication of continual, not discrete, variation), then 'torment' will prevail! Perhaps this a typical plant physiologist's view point. But I do wonder whether the amount of taxonomic splitting that has taken place in recent years (with all types of plants, fungi and lichens) has actually made it more difficult to obtain a useful picture of a taxon's distribution.

  2. I agree with Charles to a large extent, but I have a nagging feeling that variation in bryophytes (expressed as the gametophyte generation) is not precisely analogous to variation in vascular plants (expressed as the sporophyte generation). Robust orange-tinged Ctenidium superficially (indeed perhaps entirely) identical to the montane crag plants grow on base-rich rocks around Mynydd Mallaen in NE Carms at rather low altitude and in relatively deep shade. Goodness knows what we should record them as; ditto plants in upland Ceredigion etc. I think there is something genetic going on, but unravelling exactly what is the trouble.

  3. Very good point Sam. Unravelling the complexities of genotypic versus phenotypic diversity in populations with a dominant haploid generation is challenging.