A Mighty (Small) Oak and its bigger buddies

14 Apr

Quercus minima


Today John and I haunted Jonathan Dickinson State Park, near Hobe Sound Florida, finding  the flora abloom, at least in  marshy meadows,  nature’s garden complete with blooming butterworts,  orchids, meadowbeauties, milkworts, sundews, tillandsias, and too much splendor to portray with a list.

Pinguicula caerulea 3

Butterwort today.  An insectivorous plant.  All photos today by John Bradford.

The practical mission  is John’s serial  long-term photo record of “what happens after a burn.”

The blaze was about a year ago, and by now the scorched earth lies under fresh green oak boughs.   Oaks resprouted “from scratch” in a year?    Well yes, about a foot tall with no  ambition to rise higher.    These are dwarf live oak, Quercus minima, resurrecting to new life from fireproof subterranean rhizomes.

Quercus minima 2

Quercus minima towering to 9 inches tall.   The first-formed leaves are toothy lobed.

Are dwarf live oaks tiny representatives of the big  live oaks (Q. virginiana) shade trees festooned with Spanish moss across the South?    Almost.   Harvard University botany demigod Charles Sprague Sargent long ago perceptively classified both as extremes of a single species.

Quercus virginiana 8

Quercus virginiana can be huge and old.

The same question extends to a second locally abundant small oak plausibly interpretable as a variant of big Quercus virginiana.    This is sand live oak, Quercus geminata.   With variation, it is most often a shrub or smalli tree intermediate in size between big virginiana and little  minima.

What is the relationship among the three? Molecular data can settle kinship, whether for  Maury Povich or for curious botanists.    A useful DNA-centered study for today’s tree trio shows  live oak, sand live oak, and dwarf live oak together to comprise one exclusive branch on the oak evolutionary tree.  The three are most closely related to each other than any is to any other oak.    In short, it would be “legit” to see three varieties of one variable species,  or alternatively as three sister species, the latter interpretation prevailing nowadays.

Quercus germinata 3

Sand live oak

There is a compelling case for giving each its own species designation.  Chevrolet and Buick are varieties of GM yet have their own “species” identities.   Our three live oaks have diverged from a common origin over time into fairly distinct identities.    Oaks are famous for hybridizing, yet live oak, sand live oak, and dwarf live oak, all living intermixed, seem to have evolved barriers to criss-crossing, although Q. geminata and Q. minima can form a rare hybrid called Q. succulenta.     More prevalent is hybridization by each with distant cousins outside the trio.

The DNA study mentioned above is the 2015 work of botanist Jeannine Cavender-Bares and collaborators.  They noted how our  three live oaks diverge most saliently along lines of response to fire:  Q. virginiana massive, long-lived, sturdy, and intolerant of fire;  sand live oak mid-sized with grudging ability to regrow after fire; and  dwarf live oak dependent on fire.   Maybe it is all about diversification into habitats with different fire patterns.

Quercus minima hybrid

This looks like a hybrid, maybe, between dwarf live oak and Chapman’s oak.

All that said, there is an asterisk.  Quercus virginiana seedlings make a thick underground tuber before the tree grows into a mighty oak for 500 years.  Should the baby seedling be grazed, burned, or flooded it can resprout from its tuber for a second chance.   Could Quercus minima be sort of an “infantilized” live oak that remains small and took that original fireproof  temporary  “tuber” from its ancestor and expanded upon it?

Dwarf live oak has an odd foliar feature.  The earliest leaves on a branch have lobed toothy margins.  As the branch elongates, however, the younger leaves develop toothless.

Why make a transition like that?  Here is a speculation.  I think teeth and lobes on leaf margins help dissipate heat.  Maybe when the twigs are young and close to the sun-baked Florida sand below the cooling wind, where fire burned away all shade, perhaps the leaves need to shed heat.   Later, as the branches rise into the breeze, and as overhead shade increases during fire recovery, the overheating problem diminishes, making the lobed heat-shedding leaves obsolete.  Only a guess.


Posted by on April 14, 2017 in Uncategorized


4 responses to “A Mighty (Small) Oak and its bigger buddies

  1. Chris Lockhart

    April 15, 2017 at 8:23 am

    Love it! So cool to hear how the trio are related. and the speculation of the use of the toothed leaves for heat dissipation. Oaks are a fun but perplexing group.

  2. theshrubqueen

    April 15, 2017 at 2:26 pm

    Hmm, a built in early warning fan to cool the leaves. Literally a cool idea! I love to go look at all the Oaks at Hawks Bluff – it is a challenge to identify them though.

  3. Andrea

    April 15, 2017 at 7:29 pm

    George, BEAUTIFUL!!! Captivating! Love those little lobes, those are the best of all! All hail fire! Love those burns that we get,, a challenge to see what will come up…

    • George Rogers

      April 15, 2017 at 7:36 pm

      Andrea, Great to hear from you! You pyromaniac!


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