Iowa wildflower Wednesday: Common milkweed

Of the 17 types of milkweed found in Iowa, common milkweed is by far the most widespread. The use of genetically-modified Roundup Ready corn and soybeans greatly diminished common milkweed on Iowa cropland, but if you ever drive or ride your bike in the countryside, you've probably seen this plant along the side of the road. Common milkweed grows along many city bike trails too. I've posted a couple of photos after the jump, along with a bonus shot of Virginia waterleaf after the flowers have gone.

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Milkweed gets its name from the white sap that flows from the plant if you break off a leaf or part of the stem. More than 450 different kinds of insects can feed on milkweed. The plant is famously the exclusive food of monarch butterfly larvae (caterpillars).

Milkweed flowers have five petals pointing up and five pointing down. Common milkweed

can be distinguished from other milkweeds by its purplish flowers that form ball-shaped clusters and large teardrop-shaped seed pods covered with warty bumps. After pods mature in autumn, they split lengthwise releasing numerous tufted seeds. [...]

Common milkweed blooms from June to August. Seedlings do not flower until the second year. Usually, 1 or 2 flowers in each cluster mature into a seed pod. It has been estimated that a single common milkweed plant can produce 25 fruits and each fruit contains as many as 450 seeds. Seeds can float and fly and have been reported to survive at least 3 years buried in soil. Roots can grow 13 feet deep and the length of horizontal roots can increase up to 10 feet in a single season. A piece of root about 1 inch in length can produce a new plant.

I've seen tons of common milkweed blooming during the past couple of weeks.

I think the darker pink flower blooming in the far background is bull thistle, an invasive plant that's on Iowa's noxious weed list. Bull thistle can be seen along nearly as many roadsides as common milkweed. It may be Canada thistle, which is also widespread and on the noxious weed list.

The tall plant with yellow flowers blooming just to the right of the milkweed and in the mid-background of this photo is yellow sweet clover. It's native to Asia and has become a common pasture crop in North America.

The yellow flowers blooming just behind the milkweed and in the far back, to the left of the thistle, are bird's-foot trefoil. This plant is native to Europe and considered invasive in some parts of the U.S. On the other hand, many American cattle farmers consider bird's-foot trefoil an excellent pasture crop.

Here's another shot of common milkweed, with bird's-foot trefoil in the background. The clusters of buds near the top of the milkweed will bloom during the next few weeks.

Milkweed plants like sunny areas or light shade.

Todays' bonus photo shows clusters of fruit on Virginia waterleaf, which Bleeding Heartland featured in bloom here. The fruit isn't edible and looks more like peas or seeds. Each of these capsules contains two or four seeds.  Near the bottom of the picture you can see a leaf that looks like it's been splashed with water, one of the easiest ways to identify this plant.