For the naturalists among us.

Coming to south Florida from states north, the visiting naturalist musing on trees thinks of such romantic species as the Royal Palm and Gumbo Limbo.  Thoughts of oaks, a group of largely temperate zone species, are largely absent or limited to the Live Oak, that charismatic species with large arching limbs.  Even this species is more thought of as a denizen of coastal areas farther north than a part of the sub-tropical flora.  In south Florida, the West Indies Mahogany is as likely a street tree as Live Oak.

Still, away from the coastal hammocks, oak is often the dominant hardwood, and at least ten species inhabit the lower Florida peninsula.   Just a bit to the north, in the remnants of the scrublands in central Florida, is a wonderland of dwarf oaks appreciated by too few of us.  In all, Florida sports some twenty-seven species of oak, more than half of the fifty-one species found in the United States. 

The problem in properly appreciating oaks in southern Florida is that the distinctions between the species are subtle.  It is too easy to casually assume that each oak one passes in south Florida is a Live Oak.  It does not help that all of the oaks are evergreen or “tardily deciduous,” have small leaves that are somewhat elliptical, and are often little more than bushes.  Worse, the foliage on scrubby specimens is variable, so a glance at a drawing or photo in a reference may be unrewarding.  Finally, the species are in some cases so similar that botanists still struggle to separate them and continue to disagree as to which are “varieties,” “forms,” or, in fact, species.

Today, with good references on line and numerous photographs available, the process of identifying oaks is much improved from when I was a youth in south Florida.   Still, study of descriptions and on-line photos suggests that a significant percentage of the photographs are mislabeled and that the taxonomy requires more work.  We must simply recognize that every oak cannot be correctly identified.

As with any difficult group, one should start with the easy ones.  One could argue that none are easy in south Florida, but those that form and are found as true trees make a good starting point.  Among these, the most common and familiar species is Live Oak.  This species is widespread except in swamps and along salt water.  Learn to know its arching trunk and branches, thick, smooth, oval leaves with slightly down-turned edges, dark green above and glaucous below, and its small globose buds that clinch the identification. 

Live Oak is commonly planted, but so too is Sand Live Oak, a smaller, usually more slender and upright tree with convex, boat-like, leaves that show distinct grooves along the veins from the midrib and are much fuzzier underneath.  In the scrub, Sand Live Oak may be a bush with dark blue-green almost linear leaves with strongly incurved sides enclosing the densely hairy underside.  In tree form, however, the leaves are wider and much more similar to those of Live Oak.  Is it any wonder that botanists still debate whether or not they are two species?  Still, if one can learn to distinguish most Live Oak (Quercus virginiana) from Sand Live Oak (Quercus geminata), one has solved the toughest part of the “oak problem” in south Florida. 

Laurel Oak (Quercus laurifolia) is another tree oak of south Florida found on lower ground than Live Oak, often at the edge of cypress stands.  Its thin leaves are usually flat and pale, but not glaucous below.  The base of the leaf is wedge-shaped and the tip is wide and rounded. Technically its leaves are deciduous, but in south Florida, the leaves scarcely fall in winter before they are replaced by catkins and new foliage.  Laurel Oak trunks are typically smoother, narrower, and straighter than those of the live oaks, and the buds are pointed rather than rounded.

Another species, formerly and by some still included in the Laurel Oak species, is the Darlington Oak (Quercus hemisphaerica).  This species of moderately dry sandy soils is very similar to Laurel Oak, but the base of the leaf is usually rounded and the tip is pointed.  It flowers a few weeks later than Laurel Oak.

Finally, among the trees, is the Water Oak (Quercus nigra).  This species like Laurel Oak is found on moist ground.  Water Oak is similar in form to Laurel Oak, but with less dense and usually more ascending branches.  The leaves are somewhat variable in form, but typically have a wedge-shaped base and a broad and angular (spatulate) apex. As in Laurel oak the leaves are tardily deciduous. 

So, there are five species of medium to large oak trees in south Florida.  The remaining oaks are usually shrubby, but most have a classic tree structure with a single trunk.  They are most often found as members of the “scrub community” that persists on dry sands often swept by wildfire.  There, the scrub oaks form heath-like barrens that are the prime habitat of the Florida Scrub Jay and Gopher Tortoise.  Today, all but a tiny fraction of this remarkable habitat has become orange groves, streets, and housing lots.  Even on “protected ground” much of this land, over-protected from fire, has been lost as scrub community.  Only scattered patches of scrub remain on private and public properties. 

To easily find scrub oaks, one may travel north to Jonathan Dickinson State Park at Jupiter or Oscar Scherer State Park at Sarasota.  There, the spiny-looking bushy oaks continue to sprawl across the sand in association with Saw Palmetto, Wax Myrtle, and other scrub plants. 

Chapman’s Oak’s (Quercus chapmannii) 3-inch long leaves look “oak-like” having three or even five rounded shallow lobes.  The leaves are shiny above and silvery beneath.  Found on sand dunes near salt water, it is usually a shrub, but it may become a small tree. 

Bluejack Oak (Quercus incana) has 2- to 5-inch long, slender, flat leaves that are pale blue-gray above and wooly below.  The tips of its twigs appear to be dusted with pale gray ash.  The word “incana” means gray or hoary, and the word “cinerea,” an old name for this species, means ashy.  Both are appropriate.  It too is a sand-hill plant that is seldom much more than a bush.

Two shrubby species that are similar to one another and perhaps regularly confused are Myrtle Oak (Quercus myrtifolia) and Scrub or Inopina Oak (Quercus inopina).  I take their descriptions from that of the on-line Flora of North America which seems to match that of the type specimen, but others may have different views of these species.  These too may rarely become small trees.

Myrtle oak has twigs that are persistently fuzzy, leaves that are usually broadly elliptic in outline, 1- to 2- inches long, and with somewhat down-curved margins.  The underside of the leaves is typically bare except for tufts of fuzz along the veins, but sometimes yellow scurfy. The leaves of Myrtle Oak are variously oriented and often horizontal.  The plant most commonly forms a bush with attractive rounded leaves.

The similar Scrub or Inopina Oak has largely naked twigs, but they may be sparsely fuzzy at the tips.  Its leaves are 2- to 4-inches long with strongly down-curved margins that make the entire leaf strongly convex or cupped.  The undersides of the leaves are usually yellow scurfy. The leaves of Scrub or Inopina Oak often point up giving often giving the plant the form of a candleabra.This species is strictly limited to the Florida peninsula. 

Finally are a pair of very small oaks, the Dwarf Live Oak (Quercus minima) and Running Oak (Quercus pumila.)  Both species sprout stems that are scarcely shrubs and never trees from rhizomes in sandy soil.  The stems are seldom more than a few feet tall.

Dwarf Live Oak forms dense clusters of low stalks.  Its flat bright evergreen, 2 to 4-inch long leaves are of two types.  Those at the tops of stems are narrowly elliptic; those lower down are wider with several teeth on each side giving the foliage a holly-like appearance.  Underneath, the leaves are whitish.

Running Oak forms somewhat taller and more thinly foliated upright stems than Dwarf Live Oak.  Its dull green, tardily deciduous, oblong, 2 to 5-inch long, leaves are slightly downcurved at the edges and usually bear a spine only at the apex.  The lower surface of the leaves is gray-brown.   Not as handsome as Dwarf Live Oak, it has a wider range and forms scattered colonies in pine flatwoods as well as among the scrub.

In addition to these recognized species are various forms and hybrids, just to make it interesting.  Some of these may be good species, but all are vanishing with wild Florida.  Take time to enjoy them while you can.  The abundance of species and “near-species” in the Southeast suggests that the region is where the oak may have originated and certainly where it has prospered and diversified.  It is an oak-watcher’s paradise. 

Charles E. Strehl

January 22, 2010