Tuesday, 27 October 2015

Campylium on forestry tracks

Campylium protensum has made a taxonomic quantum leap from a variety of Campylium stellatum to a full species and the two taxa can be difficult to separate with puzzling intermediates. After seeing Barry's recent post on the Abercanaid road cutting, where he showed a striking population of Campylium protensum, I wondered whether we've been overlooking this species in NPT and, in particular, misidentifying Campylium stellatum.
We've recorded Campylium stellatum along a number of forest tracks, e.g. there is a significant population in the Rhigos/Cwm-hwnt forestry on the border with RCT and others in the Rheola/Resolven forests (and doubtless, elsewhere). We haven't been able to check all the populations, but we've reviewed the Cwm-hwnt plants and one of the Resolven populations.The habit and morphology of these plants are the same, so I am satisfied that, at least, they are the same taxon.
The photograph below shows the Cwm-hwnt habitat with scattered Campylium colonies.

Campylium habitat, Cwm-hwnt

The colonies are pale green, fairly compact and consist of upright plants. Typical associates include Bryum psudotriquetrum, Calliergonella cuspidata, Cratoneuron filicinum, Ctenidium molluscum and Fissidens adianthoides and you might describe this as a base-rich flush.

Campylium habit, Cwm-hwnt

The plants, which have a very nice scent (I've not seen that described elsewhere), are small but their size falls within a range for both protensum and stellatum. They are not as large as some plants I've seen in dune slacks. The are not prostrate but some plants have some pinnate branching.

Campylium, Cwm-hwnt

The Campylium key in Smith separates the two species on the basis of habit (prostrate = protensum versus upright = stellatum), the relative length of the acumen (in abruptly narrowed leaves) and in the anatomy of the leaf - whether alar cells form distinct auricles.
In all the colonies I examined, there were no prostrate plants.The longest acumen I could find was 65% of the total leaf length. This is at the upper limit for stellatum (the acumen can be much longer in protensum). Some leaves show a squarrose tendency, which is a protensum characteristic, but this is not a prominent feature (see photo above):

Abruptly narrowed Campylium leaf showing acumen

And the alar cells form distinct auricles (which is a feature of stellatum):

Campylium leaf showing alar cells and auricles (note slightly squarrose leaf tip).

On balance, I think these forestry track plants are Campylium stellatum, although the habitat may seem suitable for Campylium protensum. Comments and opinions on my interpretation please.


  1. I think your plants are C protensum, Charles, based partly on habitat, partly on the length of the acumen, and partly on overall morphology. There is some overlap between the taxa, but they are usually very distinctive and typical big C stellatum is very obvious (it's often golden-brown in colour as well). I'm puzzled by the prostrate vs upright split, as C stellatum is often sprawling whilst C protensum regularly forms turfs with upright branches. I will dig out Lars Hedenas' treatment of the species in Meylania as that will give us a definitive answer (Smith's interpretations of recent splits are not always in accordance with other experts).

  2. Hedenas' Meylania paper does agree with the characters in Smith ed 2. The split is based on morphology (erect in stellatum vs prostrate in protensum), leaf length & width, acumen length (40-65% in stellatum vs 55-77% in protensum) and potential presence of paraphyllia in protensum. Your plants look to me as though they are prostrate but with crowded upright (sub-pinnate) branches, and the acumen length in the close-up colony photo looks typical of protensum. Your observations indicate why these two have been treated as vars by many people!

  3. Interesting and provoking discussion. I must confess my experience with these species is limited, but when I saw the protensum-like plants in Merthyr last week, they instantly struck me as being distinct from dune slack stellatum which I've seen a fair amount of. Consequently I never measured the acumen, or looked critically at the specimen I took to photograph - perhaps I'd better retrieve my sample from the bin and rake a closer look? I'll certainly look more carefully in future.

  4. Many thanks Sam, I'm happy with that. I think this means that all the forestry track records in NPT (about 10 in all) are C. protensum, which is rather nice.
    I know C. stellatum well from dune slack pops and I understand what you are saying. However, I'm not totally convinced that we are not seeing intraspecific, ecotypic variation here.