Wednesday 29 October 2014
Dichodontium query
Last week I came across a Dichodontium growing on bankside reinforcements (stone and mortar) in the flood zone of the River Taff at Radyr. I assume this is most likely pellucidum but wasn't entirely confident I could rule out flavescens. The leaves are around 4 times as long as wide, which according to Smith is right on the boundary between the limits of each species. No sporophytes unfortunately. Any thoughts? Sorry my photos aren't as good as Charles's!
The photographs look pretty good to me George!
ReplyDeleteI wish I could help you with your query, but I think Sam is the only one of us who has sufficient experience to give an answer. However, I will express an opinion. Like you, I find the Dichodontium pellucidum/flavescens problem rather frustrating, particularly since D.pellucidum occurs commonly along forest tracks and along streams and rivers in NPT. In my experience, the sizes of plants vary greatly between different populations, being large and somewhat stringy on shaded river banks, but short and neat in more exposed gravelly roadsides, with intermediate sizes in other places. As a plant physiologist I would explain this in terms of a plastic, acclimation response. But taxonomists seek other solutions! Capsule morphology is a key difference between the 2 'species', but I have rarely seen D. pellucidum in fruit. Furthermore, according to a study cited by Smith, capsule morphology (in the field) can vary within single populations. Capsule morphology may also be an acclimation response. The 2 'species ' also occur in similar places. This is a nightmare for field survey and I think we need to decide on a common approach. Thanks for bringing this up.
Many thanks for your thoughts on this Charles. I note that Sam in his Pembs flora mentions he took a cautious approach and only assigned fruiting plants to species (pellucidum in all cases in that county).
ReplyDeleteI will await Sam's comments on this with regard to recording these species in the field.
I would record that as agg. I only assign fruiting plants to species except those on tracks which are all pellucidum (generally the defunct var fagimontanum)
ReplyDeleteOk, thanks Sam - I'll record it as pellucidum 'senu lato' in MapMate.
ReplyDeleteSound advice.
ReplyDeleteThere is no option for Dichodontium pellucidum agg. in Mapmate, but you can record it as Dichodontium pellucidum sens.lat., which is the same thing. If we have definitely identified Dichodntium pellucidum, then, following Sam's advice, we should add in the comments box that we observed capsules or give details of the habitat, e.g. Forest track.
Noted: there is an option to enter fruiting in the Stage field of the data entry window
ReplyDeletePS. I'll edit my records accordingly
ReplyDelete