Tracking Down Milkweeds

Asclepiadaceae flowers are unique. As are those of orchids, they are complex and took years to understand. Perhaps that is what set Dr. Rintz on the task of tracking down milkweeds.

Dr. Rintz first met these complex flowers in Malaysia through the genus Hoya. He spent time trekking through the jungle looking for these plants and found a few new species.

Hoya is a tropical genus. Since Missouri is definitely temperate, Dr. Rintz started looking at the native genus Asclepias.

Asclepias syriaca, the common milkweed, is easily spotted when tracking down milkweeds
Tracking down milkweeds like Asclepias syriaca, the common milkweed, is easy when the plants are several feet tall and lined with flower umbels. Note the typical milkweed flower arrangement: five wells around a central disc.

Dr. Woodson explored this genus back in the 1948 and wrote a monograph about it. These 200 some pages were the last full treatment of the genus until Dr. Rintz began tracking down milkweeds and studying them.

Over the course of ten years and traveling thousands of miles, Dr. Rintz found all seventy-six members of Asclepias known to occur in the United States. Some of these are very rare requiring him to get special permission to go on private lands to see and photograph them.

tracking down milkweeds is made easier by color in Asclepias tuberosa, butterfly weed
The bright orange of butterfly weed is what many people recognize. They often don’t realize this plant is a milkweed, Asclepias tuberosa, and can range from yellow to red, even bicolor. Note that this flower has the typical milkweed arrangement: five wells around a central disc. The wells may be longer than in the common milkweed, but the arrangement is similar.

As part of this study Dr. Rintz brought back preserved flowers to dissect, acquired seeds to plant and looked up many of the papers written about the quest to understand these complex flowers and how they worked.

Many botanists now confine their work to perusing herbarium sheets, studying dried and pressed plants. This process can distort the plants.

In tracking down milkweeds and studying them as living plants, Dr. Rintz found several instances when the living plants were very different from their herbarium representations. One milkweed has recumbent umbels, ones that hang down, but has the umbels pointed upward on the sheet. Two others look almost identical on their sheets, but are very different as living plants.

tracking down milkweeds is harder when the plants and flowers are much smaller as in Asclepias verticillata, whorled milkweed
Asclepias verticilata, whorled milkweed, is easy to overlook. The stem is thin, barely a quarter inch diameter and only two feet tall at most. The leaves are thin, an eighth of an inch wide. The flowers are dull in color. Still, the flowers have the five wells around a central disc.

The three volume book “Asclepias: A Study of the Living Plants” by Dr. Richard Rintz should be the new standard study of this remarkable genus. It discusses the genus in general including growing information about many of the species. It examines each species from the historical aspect and its growth. Each species is illustrated both in photographs and in dissection drawings.

Written in plain language, it is easy to follow for anyone familiar with this genus. If you are considering tracking down milkweeds or just want to seriously study them, this set is your best guide. The set is available through this website. Please request your copy through the Contact Page.