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Why are we using the name 'Dioscorea' when Stace 3 calls Black Bryony 'Tamus communis'?
... and some botanists have sunk the latter in the former. Stace didn't take up this change, but writes "(Tamus is) perhaps better amalgamated with Dioscorea ...".
Hi, in your opinion are we better using "Tamus" or "Discorea", it's just that I'm a little confused and I'm sure others are as well.
Chris Brooks - www.dragonfly-images.co.uk
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For floristic (recording) purposes there is a practical case for sticking to a fixed list, rather than following every taxomonic and nomenclatural change - it makes it easier to compare records from different years.
Both the BSBI and iSpot have adopted that approach - the BSBI have adopted the 3rd edition of Stace, and iSpot have adopted the NBN list (and unfortunately the two lists are different), but I'm not sure how stable the NBN list is.
Here the BSBI have adopted Tamus communis and iSpot Dioscorea communis.
For taxonomic purposes, there is now a consensus that taxa should be monophyletic (but reticulated phylogenies means that this is not possible for some groups). Old style botanists tended to consider too few traits, with the result that groups with distinctive derived traits were separated from the group from which they were derived. This is now being corrected on the basis of more complete morphological analyses, and especially on the basis of molecular analyses, and such groups are now being sunk. In this case I haven't studied the relevant papers, but it seems as if Stace made the wrong call here. (In the case of the Lysimachia group, the relationships haven't been fully disentangled yet, so there is a better case for conservatively retaining Glaux and Anagallis than adopting a newer classification that may be emphemeral - perhaps in the end Lysimachia may be dismembered, rather than swallowing the segregates. NBN have adopted Lysimachia maritima, to the annoyance of several people here.)
[A classic example was the separation of the three mallow genera with capitate fruits as a sister subfamily to the rest of the traditional (narrow) Malvaceae. It turns out that Malope and Kitaibelia are reasonably closely related, but Malope is closer to Malva and Kitaibelia is closer to Althaea, and Palaua is part of a mostly South American group that includes Sphaeralcea, and is closer to Abutilon to Malva. But all three below to tribe Malveae, that is are closer to Malva than to Hibiscus or Gossypium. The capitate fruits are a parallel development resulting from the increase in the number of fruitlets in a verticillate schizocarp.]
I provide records to the BSBI, and not to the NBN, so I'm better off sticking with Tamus, even if Dioscorea is more taxonomically correct (both are nomenclaturally correct) - I expect that Discorea will be taken up in the 4th edition.
I'm sorry I can't be more definite, but things aren't completely clear cut. (If I was writing a Flora I would use Dioscorea, but I'm still recording the plant as Tamus at the moment.)
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