Wednesday, July 06, 2005

Common milkweed (asclepias syriaca)

We were looking at the wild area behind our backyard and noticed a stand of common milkweeds poking above the brambles, poison ivy and honeysuckle. We thought it would be a stately plant to have and we always liked the look of the flowers and as a butterfly attractant so I decided to brave the poison ivy. I managed to dig up 5 small plants - couldn't get to the bigger ones because of the brambles but noticed that it was fairly difficult to get up out of the ground because it seemed attached to the taller ones. Later found out from some Gardenweb members that it is considered invasive and spreads by rhizomes/runners but easily controlled by pulling up the unwanted ones. I got an unwanted bonus too as I seem to have gotten some poison ivy on my foot near the toes despite wearing socks and tall rubber boots.

I also learned that the milkweed is an indicator of ozone air pollution displaying tiny black spots on the top of leaves - more meaning heavier pollution. Here's an excerpt from a website (http://pathfinderscience.net/ozone/cbackground.cfm) that describes this:

"Ozone injury on milkweed leaves is unique and relatively easy to diagnose. This injury typically results in sharply defined, small dot like lesions (stipples) on the upper surface of the leaves. These lesions are observed only on the upper leaf surface and are black-dark' purple. Veins are usually not affected. If injury is severe, it may produce an overall dark discoloration of the upper leaf surface as the lesions coalesce. The small purple dots may be observed on the damaged leaf below." and "Injury on the leaves may vary considerably! In general, the location of ozone injury on a leaf is determined by the maturity of the leaf. Acute ozone injury tends to develop towards the tip of young leaves, in the center of fully grown leaves, and at the base of the oldest leaves. Foliage frequently exposed to ozone may exhibit injury symptoms all over the upper leaf surface. Ozone damage appears as sharply defined, small dot-like lesions (stipples) on the upper surface of the leaves. These lesions are observed only on the upper leaf surface and are black-dark purple. Veins are usually not affected. If the injury is severe, it may produce an overall dark discoloration of the upper leaf surface as the lesions coalesce."

The website below shows the ozone damage.
http://www.dnr.state.wi.us/org/caer/ce/eek/earth/field/milkweed/slideshowindex.htm

So we've acquired a stately plant, monarch butterfly attractant, beautiful flowers and an ozone pollution indicator and all for free! Well not so free, my foot is itching like crazy.

Here's a link to a website if you'd like to do a project with your kids using milkweed to study ozone air pollution.

http://www.dnr.state.wi.us/org/caer/ce/eek/teacher/milkweed.htm

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