Tom's Blog

Saturday, August 2, 2008

Purple milkweed setting seeds

Purple milkweed (Asclepias purpurascens) is an Endangered Species which I have been studying extensively. The goal is to develop conservation methods to permit its establishment at new sites and get it spread more widely.

Purple milkweed is primarily a savanna species and this is where we have it at Pleasant Valley Conservancy. It first "popped up" in 1999 after our first savanna restoration work. Since then, as we have continued savanna restoration across the Conservancy, more locations have arisen. We now have 12 separate populations that have arisen spontaneously, in both bur oak and white oak savannas.

One of my focuses has been to raise purple milkweed plants in the greenhouse for transplanting at other places. Although these milkweeds are fairly easy to raise, getting good seed has been a problem. Despite good flower formation, often only a few pods form. The reasons for this are not clear.

Every year I canvas the area for pods. This year I had great flower formation but very few pods. Some pods started to form, and then aborted. The growing pods just shriveled and disappeared. Probably this was because the flowers were self pollinated. Research on other milkweeds has shown that for good seed set, cross pollination is necessary. The pollinator insect, a butterfly or bee, must pick up the pollen sack at one location and then fly to another and deposit it. Since this transfer is all very chancy, it is easy to see why pod formation might be low.

The photo here shows a good pod that is forming this year. Provided it doesn't yet start to shrivel, and the milkweed bugs or weevils don't find it, I should get quite a few seeds from this pod.


Post a Comment

Subscribe to Post Comments [Atom]

<< Home