A spongy path, softened by the reddish-brown needles of bald cypress trees, led us along the marshy shores of Yellowwood Lake’s north end.
Before our hike took us to higher ground, we stopped to admire the cypress knees, which are knobby, above-ground extensions from the roots that surround the tree trunks.
The gnarly knees create weird formations, sometimes single and other times in clusters; sometimes short and stubby and other times tall and slender.
Have you ever stared at the clouds long enough that you begin to see animals, cartoon characters and dragons? In the same way, we began to see figures in the knees: a mother with a baby, an elephant raising his trunk, a queen and king, a procession of mourners and a wizard in a long cape. The more we looked, the more we saw. There’s Chewbacca!
Like clouds, cypress knees have functions other than to amuse us. Yet botanists have debated the function of the knees for nearly 200 years.
When botanist Francois André Michaux saw knees on bald cypress trees in 1819, he wrote, “No cause can be assigned for their existence.” Since then, numerous hypotheses have emerged, some reasonable (knees function to emit methane, to store nutrients or to provide physical support) and some quite humorous (to prevent alligators from nesting).
Over the years, the leading hypothesis has been that knees work like snorkels to provide oxygen to roots growing in saturated soils under anaerobic conditions. We know bald cypress can grow in areas frequently inundated by water, as in floodplains or in swamps where the water level rises and falls with the seasons. It has also been observed that in frequently flooded areas, bald cypress grow many knees, but in dry upland soil, knees are absent or few.
But these observations alone, without experimental data, are not enough to definitively support the snorkel hypothesis. Remarkably, an experimental study published in 2015 finally tested the hypothesis. And the answer is, yes — the experimental data support the hypothesis that cypress knees provide oxygen to submerged roots.
Bald cypress trees are one of the few deciduous conifer trees; in other words, they are not “evergreen” like pines and spruces. In the autumn, the needles turn a beautiful rusty hue and fall before winter. Other deciduous conifers include tamarack, larch, sequoia and redwood.
The bald cypress trees at Yellowwood Lake are not a native population — they were planted there and throughout Indiana to control erosion and to serve as an interesting horticultural tree. Their natural distribution ranges from the Delaware Bay south to Florida and west to East Texas and southeastern Oklahoma, and up the Mississippi and Ohio rivers north to southern Illinois and southwestern Indiana.
You can visit a native stand of bald cypress in Posey County at Twin Swamps Nature Preserve, which was protected in 1987 to help conserve one of Indiana’s last stands of bald cypress.
In the meantime, take your kids on a hike around Yellowwood Lake this winter. Check out the trees with knees, and let me know if you see R2-D2 or BB-8!