Evolution of the Christmas Tree: Firs Tie Oaks in Fitness Race
In the struggle for existence, the conifers should have lost, because when angiosperms appeared, they had fancier valve jobs. That’s the feeling of a story introduced by Elizabeth Pennisi on Science Now. “Those of us who celebrate Christmas tend to take fir and spruce trees for granted around the holiday season,” she quipped, “But without a special modification that allows these trees to efficiently transport water, we might be hanging our ornaments on a ficus instead, according to a new study.” She explained:
In order for photosynthesis to occur, tall trees must supply their uppermost leaves with water, which is pulled up from the roots by evaporation. Angiosperms such as oaks and willows accomplish this using a series of centimeters-long, tube-shaped cellular pipes. Tiny valves made of cellulose membranes connect each “pipe” and help keep air bubbles out. Christmas trees and other conifers have much shorter pipe cells, however, and therefore must use many more valves than angiosperms. This should create more resistance and make it harder for them to transport water. But they don’t have any trouble at all, says John Sperry, a plant biologist at the University of Utah in Salt Lake City. (Emphasis added in all quotes.)
Sperry’s team measured water flow in 18 conifers, including bald cypress, junipers and redwoods, and compared results with 29 species of angiosperms. There was no essential difference. Conifers hoisted the water with equal ease, despite the shorter pipe cells. How do they do it?
The reason, says [Jarmila] Pittermann, has to do with key differences in the valves. Angiosperm valves are simple membranes full of miniscule pores. In conifers, the valves consist of a circle of impermeable tissue surrounded by porous tissue. The conifer’s pores are 100 times larger than those in angiosperms and allow water to pass through relatively easily. This efficiency more than makes up for the additional valves on the way to the tree top, Pittermann says.
The researchers said that this helps scientists understand water transport in wood. “But the work also points to how conifers, which predate angiosperms and are often considered primitive, were able to survive once angiosperms populated Earth,” Pennisi explains. “Without these very special cells, one biologist claimed “there wouldn’t be any conifers anymore” – presumably because they could not compete against the angiosperms. The work was published in Science.1 In the paper, the authors did not explain how or when the unique structure of the conifer valve evolved. They just said that without the adaptation, angiosperms would have a 38-fold advantage in water transport:
The superior hydraulics of the conifer pit are crucial for minimizing sapwood resistivity. If conifer tracheids had the pit resistance of angiosperms, their sapwood resistivity would increase by 38-fold…. This, added to the narrow diameter range of tracheids, would make it much more difficult for conifers to compete effectively with angiosperms.
…. We conclude that the evolution of the torus-margo membrane within the gymnosperm lineage from homogenous pits was equivalent to the evolution of vessels within the angiosperms. The towering redwoods and the sweep of the boreal coniferous forest exist in no small part because of this clever microscopic valve.
1Pitterman et al., “Torus-Margo Pits Help Conifers Compete with Angiosperms,” Science, 23 December 2005: Vol. 310. no. 5756, p. 1924 | DOI: 10.1126/science.1120479.
What did evolution have to do with this story, really? Did it contribute anything of value, even an ornament to hang on the tree? The results were not what evolutionists expected. Conifers ruled the Jurassic forests, then along come angiosperms with superior plumbing, and there should have been no contest. Those old, primitive conifers should have gone the way of the dinosaurs, and our Christmas trees would look very different. Sweep away the Darwinian mythology, and what remains? Two well-designed, highly successful groups of plants. They may have different ways of lifting water, but so what? From a design perspective, it would be just as productive a research program to find reasons for the difference. Clearly the conifers are doing well. The tallest trees in the world are conifers (see 04/22/2004). Conifers seem to do even better than angiosperms in many locations, such as at timberline, where they survive numbing cold storms and snow without even having to drop their needles. Nobody told them they were at a disadvantage against the new trees on the block.
The gem of this story is the beautifully-designed valves in conifers that allow them to pump thousands of gallons of water straight up, hundreds of feet into the air, to fill our world with beauty and dignity (see photos #1, #2, #3) while adding to the life-giving oxygen in the atmosphere. Pennisi jokingly entitled her article, “The Grinch Who (Almost) Stole Christmas” pitting angiosperms in a phony battle against their friends, the conifers. Not funny. The Grinch is Charles Darwin.