Benthamidia and Swida? Oh come one. Now they’re just making stuff up.

Oh good Lord....

Look at the new name for the dwarf Cornus. It will probably take a long time for the new names to catch on. An explanation.

Alan Weakley

The topic of genera in Cornaceae blew up in a relatively obscure post, so I thought I'd place it here front and center and step up and take the rotten tomatoes.

One of many changes that will be in the 2020 edition of the Flora of Southeastern North America is a different, new/old look at the genera of Cornaceae.

For the region, I and my co-authors for Cornaceae Derick Poindexter and Zack Ernest Murrell (the Flora of North America authors for Cornaceae) will be presenting a system of 4 genera:

Cornus (the "Cornelian Cherries"): C. mas [no native species in our region]

Benthamidia (the "Big-bracted Dogwoods"): B. florida, B. japonica (=Cornus kousa)

Chamaepericlymenum (the "Dwarf Cornels"): Ch. canadensis.

Swida (the "Blue-fruited Dogwoods": many species, including S. alternifolia.

On the other thread, some have asked for or expected that this is an "authoritative ruling". This is a "lumping/splitting" and "taxonomic rank" matter, and there are no "authoritative rulings" on such matters. This is a scientific case where there is very strong and clear evidence that there are multiple distinctive groups with long evolutionary histories and clear and many morphological differences, but at this time there is not a consensus as to whether to treat those groups as genera or as subgenera within a very broad Cornus.

Additionally, some would split further and place "Cornus kousa" in a 5th genus (Dendrobenthamia japonica) and "Cornus alternifolia in a 6th genus...

The generally prevailing opinion (maybe around the world a 2/3s to 1/3 majority) over the last few decades has been one big genus Cornus with multiple subgenera. But evidence keeps piling up about the great age and distinctiveness of the groups, and that a broad Cornus distorts what is usually meant by a genus in related families. It would be like lumping Davidia into Nyssa, or Philadelphus into Hydrangea.

The way a minority opinion on something like this becomes a majority opinion is not by some ruling by a Committee, but by persuasion and usage. By stepping up and taking the rotten tomatoes (a Solanum, not Lycopersicon -- ahem). So, we are choosing to adopt the approach of treating multiple genera in what has often been called Cornus in a broad sense. Note that we are not alone in using this taxonomic scheme. It is also in wide use in New England (following its adoption by Flora Novae Angliae in 2011 and by "GoBotany") and resembles Small's 1903/1913/1933 recognition of Cynoxylon and Svida (and no Cornus in the southeastern United States).

Text explaining the choice:

A family of 5-6 genera (as here interpreted) and about 85 species, trees, shrubs, lianas, and subshrubs, semicosmopolitan (mainly northern hemisphere). The Cornaceae is best circumscribed to exclude Nyssa, which probably is not even sister to Cornaceae (Xiang et al. 2002; Fu et al. 2019). The generic limits within core Cornaceae have long been controversial. The segregate genera of Cornus used here date back to 1756-1839, and in the southeastern United States, Small (1903, 1913, 1933) treated our native species in Cynoxylon and Svida. Phylogenetic analyses show that Cornus treated very broadly is monophyletic, but various clades within it are also monophyletic and have ages and levels of genetic and morphologic divergence generally regarded as warranting generic distinction. Fu et al. (2019) estimate the five major clades (including four in our area) as having divergence times of 60-75 million years ago (about at the end of the Cretaceous). Yu et al. (2017) estimate that the major clades in Cornaceae (including the separation between Alangium and Cornus s.l.) date to 66-85 million years ago, with the exception of the split between the big-bracted dogwoods (here treated as Benthamidia) and the dwarf cornels (here treated as Chamaepericlymenum). In all other families of the Cornales, clades with divergence times of such age are universally treated as separate genera, and separation times of half that are often accorded genus rank. Based on our increased knowledge of the age and distinctiveness of these groups, it seems almost certain that the traditional ‘subgenera’ will be recognized by consensus in the future as warranting generic rank, and we treat them so here, but that decision will be controversial. Eyde’s (1987) irritated and impassioned defense of a "broad Cornus" remains influential and is still followed by many -- though its reasoning seems increasingly irrelevant following a third of a century’s elucidation of the relationships within Cornaceae and related families."

I blame Covid. Not enough to do.

A cockamamie COVID Cornus consortium of contrarians with...

♫ Too, too, too, too, too much time on their hands... ♫

tj

I just give up...everything's name will remain forever static for me. We have Asters (not Symphitrchium or whatever it is..don't care), we have Cornus, we have Myrica (Bayberries), nope nope..just ignoring taxonomy changes from now on.

It seems like giving everything one's own personal treatment is all the rage these days , which makes all the discussions more colorful, when folks like you, use the old, obsolete, archaic names LOL, so it's all good. Some people in my native plant society still use the old names like Andropogon scoparium.I just wish these new names were easier to pronounce, with less syllables, Symphyotrichum is a great example. I can't possibly remember all these names and their spelling. I always check spelling before writing anything out. All this DNA analysis was going on, way before covid, but I think covid has spawned a lot more botanical outings and research studies. There are a lot of species in North America that don't fit into any other species perfectly, and these will probably become new species.

Do notice that in the above excerpt the alternative naming Weakley is mentioning already exists - and in some instances was proposed a long time ago - and he is merely claiming that the argument for adopting it has become stronger. That it isn't, in fact the case that the dogwoods have just lately been split up and given a full suite of replacement names all created very recently.

I think you'll find that when plants are reclassified, the "old, obsolete, archaic names" are retained as legitimate synonyms. And as noted above, this reclassification has been under discussion for sometime and as of yet, has not been officially sanctioned.