Friday, April 1, 2011

Darlington oak?

In a (fairly) recent post I talked about how a tree in Covington Cty, MS had usurped a tree in Howard Cty, AR as the biggest Arkansas oak (Q. arkansana).  I found this somewhat noteworthy/amusing because a) the range of Arkansas oak consists of a few widely scattered dots across the South, and most range maps I have seen don't show any of those dots occurring in Mississippi, and b) I have grave doubts as to whether Arkansas oak is truly a species - even to the very limited extent any oak species can be considered a true species.

As they say in the journalism trade, this story is still developing.  A forester in Howard Cty, AR has very kindly agreed to seek out the tree that held the title of champion until 1997, take photos and collect leave/twig/acorn samples for me.  Another forester friend in MS who believes the Covington Cty tree might be misidentified is looking into this further, and will help compare the samples.

It will be interesting to see how two trees from hundreds of miles apart, both classified by people who - by virtue of the fact that the population is sparse, spotty and by all indications in decline - have seen very few Arkansas oaks, compare.

But none of that is what this post is about. 

I was looking at the registry of Champion Trees of Mississippi  to try to learn more about the who & how of the Covington Cty Arkansas oak nomination when two things caught my eye:

1) The MS state registry includes 24 species of oak.  24!  Here in Minnesota we have 7 species, and that includes those chinkapins no one has seen in more than a century.  Let's call it 6.

2) The MS state registry has a listing for Darlington oak, Q. hemisphaerica.  Darlington oak?  I don't pretend to be an expert on southern oaks, but I had never even heard of Darlington oak.  It's not listed in Oaks of North America, the highly flawed but mostly complete reference I generally turn to.

So I went here to learn more.  I will lift the taxonomy section in whole:


The scientific names of Darlington oak and laurel oak are Quercus hemisphaerica Bartram ex Willd. and Quercus laurifolia Michx. [4,8,40,43,49,50]

The historical nomenclature of these oaks is complicated. In the past, most authorities, including Little [24], treated them as a single species but differed on the appropriate scientific name [43]. More recent authorities [4,8,40,43,49,50] recognize two species, Q. hemisphaerica and Q. laurifolia, based on anatomical differences and vast differences in site preferences. Laurel oak (Q. laurifolia) grows in wetlands. Darlington oak (Q. hemisphaerica) grows in uplands; it has acute leaf tips and flowers 2 weeks later than laurel oak in the same area [8,12,27]. In many cases, the literature treats Darlington and laurel oaks as one species. Information from authors that recognize and discuss Darlington oak and laurel oak as a separate species is included and noted as such.

Darlington and laurel oak are placed within the subgenus Erythrobalanus, or black (red) oak group. Laurel oak is difficult to identify and is often confused with willow oak (Q. phellos) and water oak (Q. nigra) [40]. It
has been suggested that laurel oak is a hybrid between these two species, but that may not be the case because willow oak is absent from southeastern Georgia and peninsular Florida where laurel oak is abundant

Laurel oak hybridizes with the following species [24,27]:
x Q. falcata (southern red oak): Q. X. beaumontiana Sarg.
x Q. incana (bluejack oak): Q. X. atlantica Ashe
x Q. laevis (turkey oak): Q. X. mellichampii Trel.
x Q. marilandica (blackjack oak): Q. X. diversiloba Tharp ex A. Camus

Glad we could straighten that out!  So Darlington oak is a kinda sorta maybe/maybe not species depending on who you talk to and even then bears several Latin binomials.

I am beginning to see why - and feel a lot less jealous about - the Southern states having so many more oaks than we do in Minnesota:  They don't.  They have a few species and just call them each about a dozen different things.  I think it's a plot by Southern foresters to make northern foresters feel stupid (it's working).

When my head was starting to ache I called an oak expert in Mississippi for clarification, which he did in the same way that the Mississippi River becomes clearer as it flows from me to him... which is to say like mud.  But that's good.  The muddiness of oak taxonony is something we both understand, so for me what he had to say made perfect sense.

When I mentioned Darlington oak his response was, "Oh yeah, that's another one of those water oaks."  Another one of those water oaks (Q. nigra)?  How many are there?  Depends on who you talk to.  Water oak, laurel oak, swamp laurel oak, Darlington oak and probably Arkansas oak all fit that category with many overlapping traits - many of which are probably more a reflection of site characteristics than the inherent genetics of the trees themselves.

He then said, as usual, something completely brilliant: Throughout the South there are localized clusters of oaks of a particular species that exhibit a set of variant traits (longer acorns, later/early leaf out or leaf drop, wider or narrow spatulate leaves, etc.).  Taxonomists are keen to either label this localized variant as a distinct variety of a particular species, or even as a separate species in and of itself.  When another taxonomist finds a localized cluster of trees 200 miles away that exhibit the exact same slight variations, they name it something else yet again.  So instead of one species with a wide set of local variations we now have, depending on who you talk to, 3 distinct species, 2 distinct species and 1 variety, 1 distict species and 2 varieties, of any number of hybrids.  Then the taxonomists spend their carrers arguing about it.

That is work I would seriously enjoy.

Here's the truly interesting thing (to me at least):  The MS state champion Darlington oak was nominated by Mr. B. E. Brown - the same guy who nominated the Arkansas oak in Covington County.  Could it be that Mr. Brown is seeing local variants of water oak and classifying them as a more narrowly defined "species?"

Stay tuned.

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