Sunday, August 26, 2007

The Compass Plant

The blooms of the Compass Plant are the yellow ones at the top. They're nice and all but its the leaves at the base that have the nifty secret.
The fourteen foot Compass Plant being pointed out by one of the Tall Grass botanists.
I'd been meaning to make a visit to Tall Grass Restoration's acres and acres of prairie, ever since I ran across their sign. Particularly after I realized that a very high concentration of Red-tails seemed to be hanging around the edges sitting on power poles scoping out dinner. On Saturday I finally did it. It' a grand place which I'll say more about in a future blog but one of my big surprises of the day was the Compass Plant.
The Compass Plant was used by Native Americans and then by the pioneers in order to orient themselves. Walking around in grass taller than one's head can sometimes be directionally challenging. There are few landmarks directly above one's head or actually not so many of any kind in the topography locally anyway. On cloudy days or at night the sun isn't really all that much help.
The Tall Grass folks use a big Hickory on a slight knoll when they find themselves disoriented while working on the prairie. Well, that and the Compass Plants. Note the position of the leaves above.

The leaves at the base of the plant align themselves north and south. In other words the edges are north/south and the flat of the leaves are east/west. Just how cool is that? And it tends, even in mature tall grass prairie to be one of the tallest plants so you can see it above the other grasses.
I like it so much in fact, it tends to make me smile just thinking about it. Its a wonder in the true sense of the word.
Here's the abstract of a paper about Compass Plants , which you can access at the library through JOSTER.

"Leaves of Silphium laciniatum L. are nearly vertical and have compass orientation, i.e., the surfaces face east and west. We studied the manner in which compass orientation develops. Compass orientation was verified by measurements of azimuths for three sets of leaves in the field.

Averages of leaf azimuths were 77, 86, and 87 degrees from north. Averages of the absolute value of the differences between leaf azimuth and (east/west facing) were 24, 32, and 15 degrees. Adaxial and abaxial leaf surfaces were equally likely to face east. Newly emerged leaves had random orientation, but within 2-3 weeks compass orientation was achieved by twisting of the leaf petiole. Leaves turned either clockwise or counterclockwise, whichever produced compass orientation with the minimum amount of turning.

Orientation involved a growth response; the ability to orient was lost on completion of leaf expansion. Directional sunlight cues were necessary for compass orientation to occur; leaves provided with only overhead light exhibited random orientation.

In the absence of directional light, leaves displayed an endogenous, unidirectional turning pattern; a majority of leaves turned counterclockwise. We hypothesize that endogenous turning enables leaves to sample the light environment and that leaves use the position of the sun in the early morning to determine compass orientation."

This journal is licensed to JSTOR by Torrey Botanical Society

Development of Leaf Orientation in the Prairie Compass Plant, Silphium laciniatum L. Hanzhong Zhang, John M. Pleasants, Thomas W. JurikBulletin of the Torrey Botanical Club, Vol. 118, No. 1 (Jan. - Mar., 1991), pp. 33-42doi:10.2307/2996973This article consists of 10 page(s).
Donegal Browne

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