The Beauty of Holiday Trees is More Than Bark-Deep

If you are one of the many people who head out into the woods, to the tree farm, or to the corner lot each year to find the perfect holiday tree, you know what your favorite tree looks like on the outside. But do you know what it looks like on the inside and magnified 400 times?  FPL’s Center for Wood Anatomy Research can give you a peek at the secret inner workings of several of the most popular holiday tree species in the United States.

The True Firs

For some time, the single most popular holiday tree in the U.S. has been the Fraser Fir. The Fraser is much loved for its persistent green and silver needles, good form, and pleasant odor.  Closely related to Fraser Fir are several other true firs, including Balsam Fir, White Fir, and Noble Fir.

The microscopic wood anatomy of the true firs as a group is fairly consistent, with the primary differences being the presence of small calcium oxalate crystals in the ray cells of species in the white fir group.  Crystalline materials have the physical property of birefringence, which is a bending of light – this lets the crystals shine out against a black background when viewed with polarized light microscopy and shows off some of their hidden beauty.

(L) Radial section of white fir showing calcium oxalate crystals (arrows). (R) Polarized light micrograph of the exact same cells as on the right. Note the crystals (arrows) shining out against the dark background.

The Pines

Second only to the true firs, pines are among the most classic holiday trees regardless of where in the country you live. Three species top the list: eastern white pine; Scots pine; and Virginia pine.

Eastern white pine is beloved for its long, soft needles borne in clusters of 4-5 and its graceful branches.  Under the microscope, white pine wood is a flagship example of the white pine group; in fact, in colonial times the British harvested mature trees as prime mast wood for their navy (pun intended).

Radial section of eastern white pine showing classic white pine features: smooth ray tracheids (arrows) and fenestriform cross-field pits (arrowheads).

Radial section of eastern white pine showing classic white pine features: smooth ray tracheids (arrows) and fenestriform cross-field pits (arrowheads).

Scots pine, a European native grown in plantation in the U.S., is favored for its short, twisted needles and slightly orange bark. From a wood anatomical point of view, it is an archetypal member of the red pine group, and its wood cannot be definitively separated from North American red pine, much to the dismay of many an antique dealer.

Radial section of Scots pine showing classic red pine features: dentate ray tracheids (arrows) and fenestriform cross-field pits (arrowheads).

Radial section of Scots pine showing classic red pine features: dentate ray tracheids (arrows) and fenestriform cross-field pits (arrowheads).

Virginia pine grows natively in the American southeast, but its closest relatives are not other Southern pines, but rather Western yellow pines.  Despite the long distance to its nearest kin, it is a well-loved alternative to Scots pine, and is a perfect example of all its relatives in the larger yellow pine group to which it belongs.

Radial section of Virginia pine showing classic yellow pine features: dentate ray tracheids (arrows) and pinoid cross-field pits (arrowheads).

Radial section of Virginia pine showing classic yellow pine features: dentate ray tracheids (arrows) and pinoid cross-field pits (arrowheads).

Douglas-fir

Not actually a true fir, but instead a member of a completely different genus, Douglas-fir is a full, stately holiday tree valued for its ability to fill large, open spaces. Douglas-fir is an eye-catcher beneath the bark and seen with the microscope, too – helical thickenings are abundant in the earlywood tracheids but not the latewood tracheids, and set apart the wood of this tree from almost all other conifers.

Radial section of Douglas-fir showing the abundant helical thickenings in the earlywood tracheids (arrows) and the absence of helical thickenings in the latewood tracheids (arrowheads) on the far right.

Radial section of Douglas-fir showing the abundant helical thickenings in the earlywood tracheids (arrows) and the absence of helical thickenings in the latewood tracheids (arrowheads) on the far right.

As you decorate your tree this year, take a moment to appreciate the minute, inner beauty and splendor waiting to be seen just beneath the surface.

 

Contributed by:  Alex C. Wiedenhoeft, Adriana Costa, Rafael Arévalo, Richard Soares, and Mario Ramos.