An Overview of Ohio Dogbane and Milkweed Species (part 1 of 3): Dogbane Species

For my first post, and for a few subsequent posts, I will be talking about dogbane and milkweed species. Dogbane and milkweed can be tricky to tell apart. Many people think milkweed is easy to identify because it has milky sap, but if you go and tear a dogbane leaf off the stem, you'll quickly realize that other plants have similar milky sap. The leaves of these two plants look quite a bit alike too. I will concentrate on these differences in a later post.

For this post, I would like to concentrate on the different species of dogbane found in Ohio, and how to tell them apart. Here in Ohio, there are four species of dogbane: clasping dogbane, Indian hemp, intermediate dogbane, and spreading dogbane. The name "dogbane" refers to the fact that the plant is toxic to dogs. In general, dogbane has opposite leaves, milky sap, and can form branches, usually right above the petiole of a leaf. The leaves tend to be oval, and have a vein pattern that seems to form a series of loops. The leaves are smooth, not serrated, and have a distinct "tip" at the end. The stems are green or reddish/brown in color, and are smooth, lacking hair. Towards the top of the plant, there tends to be a great deal of branching. The flowers form in clusters and are generally small (a quarter inch long) and are composed of 5 petals. The seeds of dogbane are generally long and narrow, forming clusters of 2 pods. Dogbane is widespread throughout the US.

1: Clasping Dogbane
The first species I have to talk about is clasping dogbane. Clasping Dogbane tends to be anywhere from 1-4 feet tall. It generally blooms in the summer, producing greenish-yellow flowers that have 5 petals, are bell-shaped, and about a quarter-inch long. Clasping dogbane has leaves that look a lot like those of Indian hemp. The easy way to tell the difference between the two is to notice that the leaves tend to clasp around the stem. This feature is unique to clasping dogbane.

2: Indian Hemp

The next species I have to talk about is Indian hemp. Indian hemp is one of the more common plants I come across. To me, it seems to look a lot like common milkweed, only smaller leaf sizes. Indian hemp doesn't resemble intermediate or spreading dogbane that much, but it does look similar to clasping dogbane. It is about the same size, with similar flowers (tending to be whiter). Some field guides and references I have seen DO categorize Indian hemp and clasping dogbane as the same species, however enough references that seem more reliable have separated these two, and therefor so will I. I could give a number of generalities that allow for the distinction of these two species, however I feel that only one distinction is necessary. Indian hemp leaves do not have the same clasping effect that clasping dogbane has, and Indian hemp leaves have a short, distinctive petiole.

3: Intermediate Dogbane

Intermediate dogbane looks different from Indian hemp and clasping dogbane. It's leaves tend to be shorter, only about 2"-4" long. It's stem tends to be a dark brownish-red, whereas the stems of Indian hemp and clasping dogbane are a green color, with a slight reddish hue. Intermediate dogbane, however, does resemble spreading dogbane quite a bit. Intermediate dogbane gets its name because it is the cross between Indian hemp and spreading dogbane. There are no really easy ways to tell intermediate dogbane apart from spreading dogbane, but I have a few tips. First, lets look at the vein pattern on the leaf. The series of vein loops on intermediate dogbane tends to be more bunched up, and the loops are a lot thinner. On spreading dogbane, these loops are a lot wider, almost squarish. If you look at the leaf petioles, intermediate dogbane has a well defined petiole, where spreading dogbane leaves barely have any petiole. I have noticed that intermediate dogbane generally has white flowers, where spreading dogbane has pinkish-purple flowers, however, intermediate dogbane may have other colors of flowers. 

4: Spreading Dogbane

Spreading dogbane also doesn't resemble clasping dogbane or Indian hemp, but it does represent intermediate dogbane. I feel that stating the differences between spreading dogbane and intermediate dogbane again would be redundant, so I will refrain from doing so. Instead I will skip to giving specifications on spreading dogbane. Spreading dogbane tends to be from 1 to 3 feet tall. Their leaves can be anywhere from 1"-4" long, with short petioles and a spike at the end. Their flowers are bell-shaped with 5 pinkish/purplish petals. Their stems are a dark red/brown color.

That is all I have for this evening. Tomorrow I will talk about the milkweed species of Ohio. Hopefully this blog can grow a bit. The pictures of the dogbane species that I have posted are not mine. The only picture on this blog that is mine is the picture of the milkweed beetle set as the header. I plan on replacing these dogbane pictures with pictures of my own when I can locate them to photograph.