As we crossed a sunny field with milkweed (Asclepias syriaca) and dogbane (Apocynum cannabinum) growing in abundance, an animated conversation ensued as to which was which. Studying a plant in all seasons provides a valuable opportunity to note similarities and differences.
Yes, dogbane and milkweed do grow together, as shown in this photo I found online:
This spring photo reveals the subtle differences in the size and shape of the leaves, but other features provide a more readily visible distinction in the field. Yesterday, it was obvious that some plants had smooth stems and some had fine hairs.
Page 299 from The Forager’s Harvest has a very handy chart listing the basic field identifiers between the two. Here are a few highlights:
Milkweed has fine hairs on the stem and leaf bottom.
Dogbane stem and leaf surfaces are smooth.
Milkweed has few, if any buds on its leaf axils.
Dogbane has many leaf axils with buds.
Milkweed leaves do not squeak when rubbed together.
Dogbane leaves squeak when rubbed together.
Milkweed leaves are smaller ascending the stalk, larger lower on the stalk.
Dogbane leaves are slightly larger ascending the stalk, smaller at base.
Milkweed stalks are hollow and green inside.
Dogbane stalks are solid and white or cream inside.
Milkweed stalks are slightly squared in cross section.
Dogbane stalks are round in cross section.
Milkweed exudes lots of milky latex sap.
Dogbane exudes a little bit of milky latex sap.
The only way to learn field characteristics is to spend time in the field, note details of the plant, fungus or animal and consult many experts for references to these details.
Sometimes the pursuit results in an identification. Often, it’s like being a detective, with the answer revealed months or years later. As knowledge is gained and information updated, many ideas once thought to be true are now considered false. Distinguishing milkweed from dogbane has moved milkweed from inedible to edible for many foragers.