Mystery oak grows up to 60 feet in eastern U.S.

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A small tree, with very desirable wood.

So said the eminent Harvard botanist Asa Gray, on page 451 in his encyclopedic "Lessons in Botany and Vegetable Physiology," a book published in 1872. I got my copy at an old book store several years ago; can't remember where exactly. The book is some 700 pages long, not including a series of gorgeous line drawings of sedges, grasses and ferns in the back. The pages feature fore edge marbling - a bit faded now - and the front and back covers are ornamented, with the monogram of the publishing house. They don't make books like this anymore.

Professor Gray was, of course, referring to what we have as this week's Mystery Plant. I'm pretty confident that all you botanists out there will recognize this instantly as some sort of oak. Oaks belong to the genus Quercus, and they are not always large trees. Some species, of course, are called "scrub oaks," which seems to me a bit of a botanical "put-down," and other species are good examples of shrubs, not more than about knee-high.

Here in the Southeast we have about 45 native oak species, most of which can rather easily be differentiated into two groups: "White oaks," including our Mystery Plant, have rounded lobes without any points or bristles on the tips. "Red oaks" feature sharply pointed lobes, each with a prominent bristle at the top. There are some other differences, too.

Our Mystery oak is widely distributed in the eastern U.S., from southern New England through Missouri and Texas, and then east from there, including northern Florida. It is a deciduous species, producing pale, somewhat shreddy or scaly bark. Really large, old individuals can be over 60 feet tall, and because of this, they make great shade trees along city streets and in parks. The acorns take one season to mature, and they are a valuable wildlife food source.

What most people remember about this species are the leaves. The leaves are bright green and scratchy on the surfaces. Generally, the leaves have a distinctive cross-shaped (cruciform) look, with two major lobes projected more or less horizontally from the midrib. The cross shape is not always well developed from individual to individual, however, especially if there has been any hybridization going on. Oak species are famous for mixing it up with each other.

The best way to recognize this species is by taking a look at the lower surface of the leaf, which will show off thousands of tiny, branched, star-shaped hairs; that is, "stellate" hairs. You'll need a hand-lens to be able to see these hairs, but I know that you have one.

And this is interesting: Professor Gray refers to this oak in his book by using an incorrect name. The correct and first valid name came about in 1787, penned by a German botanist named Friedrich von Wangenheim. But for some reason Gray printed the name Quercus obtusiloba, which had been proposed by the French botanist Andre Michaux. But Michaux was 15 years late; je regrette.

Answer: "Post oak," Quercus stellata

John Nelson is the curator of the A.C. Moore Herbarium at the University of South Carolina, in the Department of Biological Sciences, Columbia SC 29208. As a public service, the Herbarium offers free plant identifications. For more information, visit www.herbarium.org, call (803) 777-8196, or email nelson@sc.edu.