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Differential Morphology: Milkweed and Dogbane

Updated: Jul 3

Most people who are acquainted with Milkweed know it as the “Monarch Butterfly host plant.” If you do a quick search for news headlines discussing the plant, you’ll rarely find one that doesn’t pair it alongside its mutualist pollinator. And it's not just monarchs that appreciate milkweed's alluringly fragrant blossom– over 450 different invertebrates are known to feed on on common milkweed. One could argue that milkweed is the poster child for invertebrate–plant relationships, and it does a pretty stellar job of illustrating the importance of these types of ecological relationships.


When I speak about milkweed as a wild edible, the question I most frequently get is whether it is a good idea to be harvesting from a plant that plays such an important ecological role. Milkweed does host many invertebrates, and it is the exclusive host plant for the Danaus plexippus, the Monarch butterfly. Monarch populations are currently in decline, and the reason for this is habitat loss– name, reduction in milkweed populations. This is primarily due to agricultural development, as well as the ever-increasing sprawl of urban and suburban development. Monarchs don’t just need milkweed plants for reproduction, they need dense stands of milkweed, because the caterpillars that drop off the plant to escape predation need to be able to find their way quickly back to a milkweed stem. So, while at first glance it may make sense to leave the remaining milkweed plants we come across alone, the solution is, actually, quite the opposite. 


Milkweed has existed in abundance, in part, because of its history as a culturally important plant. Indigenous people all across the Turtle Island have tended and propagated milkweed, as it was not only a staple food and medicine plant, but a highly valued fiber plant as well. And when it comes to fiber plants, you need a lot of plants. It has been reported than the Sierra Miwok people required 35,000 milkweed and Dogbane stalks to make the 7,000 feet of cordage required for a single 40’ deer net for hunting, and the Washoe and Northern Paiute people used over 60,000 stalks to make 12,000 plus feet of cordage needed to weave a 100’ fishing gill net. It is hard to imagine the massive quantities of these plants that were harvested all across North America every year. 


Desiccated dogbane stems and seed pods, ready to be harvested for cordage

If we continue to act as we have– avoiding milkweed for fear of over-harvest while land use continues to drive populations into the ground– the situation is only going to get worse. Conversely, if we choose to develop an intentional, mutualistic relationship with milkweed, in which we harvest the edible portions while actively propagating and tending stands in areas where they are most likely to thrive, away from the risk of being mowed over or bulldozed for development, then milkweed stands a chance at making a comeback–along with the Monarch that depends on it. More foragers with a heartfelt connection to milkweed and a pinch of education means more stewards to care about the plant and act in its best interest. And plants of the Apocynaceae make an easy gateway into wildtending, with their easy to harvest seeds (the follicles open when they're ready for harvest, so there's no guesswork as far as when to collect them), rhizomatous spreading roots, and general hardiness (common milkweed even transplants quite well).


Cardiac Glycosides found in the Apocynaceae


Milkweed and Dogbane species both contain cardiac glycosides, also known as cardenolides. These are molecules in the same class as digitoxin, found in Digitalis species, or Foxglove. However not all Apocynaceae plants contain the same type or amount of CGs.  Plants in the Dogbane genus contain a more toxic type of cardenolide, and in much higher concentrations than the milkweeds. However, not all milkweed are created equal either in regards to their cardenolide composition. 


The kind of cardenolide found in the Apocynum genus is called cymarin. While cymarin has some history of use as traditional medicine, and has been studied for its potential pharmacological uses as a cardiotonic and antitumoral agent, it is not used in modern day due to its high risk of toxicity. The cardenolides in Dogbane produce an intensely bitter flavor, which is absent or nearly-so in the edible species of milkweed. 


Some species of Asclepias, such as A. verticillata (whorled milkweed) and A. incarnata (Swamp milkweed), contain little to no cardenolides but are known to be neurotoxic, due to a different unconfirmed compound, potentially pregnane glycosides. 


It should be noted that while research into the chemical composition of milkweed plants is ongoing, ethnobotanical records are invaluable in regards to understanding the potential of various milkweeds for food and medicine. For example, Asclepias tuberosa, also known as butterfly weed or pleurisy root, has an extensive history as a medicinal herb amongst many indigenous peoples of the North America, however it does not appear to have been regarded as food. Asclepias syriaca, on the other hand, is a well-known traditional plant, with the spring shoots, leaves, flower clusters, and seed pods, consumed by a plethora of indigenous groups across eastern and midwestern Turtle Island. Asclepias incarnata, in contrast, was known to be consumed by the Menominee people, but there is only record of the flowerheads being used as food– not the shoots or other plant parts. The Lenape people had two different words for milkweed, one for the edible types (pitukëna), and one for the non-edible types (mahkhalahpis).


Asclepias syriaca (common milkweed) and A. speciosa (showy milkweed) are the most commonly cited species of milkweed of which all parts were consumed by indigenous people, and still are still common and much-valued elements of indigenous cuisine today. So, while we wait for western science to catch up to traditional knowledge, it is safe to say these two species are safe to consume and widely well tolerated by most individuals. It is worth noting, however, that even these two species of milkweed do contain enough cardenolides to warrant the need for proper preparation (more on that below) and should be avoided in individuals with heart conditions and/or on heart medications as a precautionary measure. 


Plants like milkweed that produce cardenolides as a protection against herbivorous predators, however a number of invertebrates have evolved to be able to feed on milkweed and sequester the cardenolides in their bodies, making them unpalatable or even toxic to predators. They have an altered sodium-potassium pump enzyme which provides them with  50-fold increased resistance to the ill-effects of the cardiac glycosides compared to other types of insects. Monarch butterflies are a well known example of an invertebrate that feeds on milkweed and accumulates cardenolides, preventing avian predation. For most birds, consuming insects which have been feeding on plants containing, will induce nausea and emesis. However some birds, such as Pheucticus melanocephalus, the Black-headed Grosbeak,  have evolved an insensitivity to the effects of cardenolides via the same sodium-potassium pump enzyme alteration. Also, not all cardenolides are equally emetic (non-polar cardenolides being less emetic than polar ones), so variations across species and potentially seasonal and regional variability determine how much a plant will affect invertebrate biochemistry and thus, predator-prey interactions.


Ants don't eat milkweed, because they haven't adapted to withstand its toxins- but they do feed on its nectar, and they also consume honeydew from aphids, and they will often "farm" aphids on milkweed plants

Milkweed as Food


The first step on your way to eating milkweed is to ensure you have the appropriate species. Dogbane is not edible, and it should not be consumed. Not all milkweeds are edible, either. As mentioned above, the two safest bets for vegetable-quality milkweed are Asclepias syriaca (common milkweed) and A. speciosa (showy milkweed). Showy milkweed is mostly found in western North American, whereas Common milkweed is found in the east. The following instructions may be applied to either species.


One last step after positive identification before you move on to cooking is to inspect the plant for insects and insect eggs. Monarch caterpillars should be returned to the plant, and leaves with eggs attached should be left on the plant to hatch. 


There is conflicting advice in the wild foods community about how important it is to cook milkweed. While these two species of milkweed are safe to consume raw in small amounts for most individuals, some people do seem to be more sensitive to the ill effects than others, reporting indigestion. The general recommendation is to cook it, and since milkweed lends itself so well to cooked dishes, it doesn't feel like a loss to me to avoid eating it raw. 


Shoots: Shoots should be harvested when they are still tender enough to break off without the need for a knife. For shoots, this is generally under 14” in height, but the upper, meristematic portions of taller plants can still be harvested. Shoots should be cooked, blanch in boiling water for 1-3 minutes and then you can prepare them however you’d like. 


Flowers: Unopened flower buds are preferred, as once the flower opens the pedicles become slightly less tender. These do not need to be boiled before consumption– a light sauté or cooked into baked dishes or soups is sufficient. Milkweed blossoms have an intensely sweet floral aroma and flavor, which can be enjoyed on their own or added to dishes for an enticing twist. 


Seed Pods: Harvest the young, green seed pods when they are still soft and squishy if you wish to consume them whole. At this stage the immature silk inside will still be completely white, with no brown bits. For pods that are slightly past this stage, you can still harvest the silk from inside the pod and it will still be palatable. If you miss the window entirely, however, and the seed pods are fully mature seed pods, they will be too tough to eat. Pods don’t store very well and tend to toughen up rather quickly, so if you don’t plan to cook them and eat them right away, blanch and freeze them. Otherwise, pods can be prepared similar to the flower buds– no need for boiling. 


Apocynaceae identification and Differentials


Below I will outline the morphological features of some common Apocynaceae species in the central Pennsylvania region. 


Apocynum cannabinum - Hemp Dogbane



Dogbane has more lithe character than the milkweeds, with the spreading branches and delicate clusters of little flowers. It is easy to identify as it matures, but during its early Spring shoot growth stage, it is a toxic look-alike for common milkweed (more on that below).


Morphology:

  • Erect, branching plant, growing up to 5’ tall

  • Stems are glabrous, often glaucous, terete and solid upon cross-section

  • Leaves are opposite, ovate, oblong-lanceolate, or elliptic, and may be glabrous or pubescent on the underside

  • Flowers are erect, growing in sparse axillary and terminal cymes

  • Flowers are white

  • Fruits are long, thin, bean-like 5-8” long follicles that grow in conjoined pairs

  • Roots are rhizomatous

  • Exudes white milky latex when cut


Asclepias syriaca - Common Milkweed



Morphology:

  • Erect, non branching plant, up to 6.5’ tall

  • Stems are slightly to moderately pubescent, slightly square and hollow upon cross-section

  • Leaves are opposite, broad– oval to oblong-lanceolate

  • Flowers grow in dense, spherical umbels, appearing mostly at the terminus of the plant

  • Flowers are most often pale pink or pinkish-purple, but range from whitish-green to purple

  • Fruits are 3-4” long tear-drop shaped pubescent follicles, covered with soft prickle-like projections

  • Roots are rhizomatous

  • Exudes copious white milky latex when cut


Milkweed on the left vs. dogbane on the right


Asclepias purpurascens – Purple Milkweed


Purple milkweed

Morphology:

  • Erect, growing up to a 3.25’ tall

  • Leaves opposite, broad– elliptic to oblong-ovate, veins more reticulate and irregular than A. syriaca

  • Flowers in 1-6 terminal, or rarely axillary, many-flower umbels, purple

  • Fruits are pubescent but lacking prickles





Asclepias incarnata - Swamp Milkweed


swamp milkweed
Swamp milkweed with unopened flower buds

Morphology:

  • Erect, branching plant at the top, growing up to 5’ tall

  • Stems glabrous to slightly pubescent

  • Leaves opposite, lanceolate to oblong-lanceolate, sessile or sometimes clasping

  • Flowers in several clustered umbels, varying colors of pink

  • Fruits are erect, smooth narrow follicles, 3-4” long

  • Grows in damper conditions than the other species mentioned here

  • Roots are rhizomatous


Asclepias tuberosa - Pleurisy Root



Morphology:

  • Erect, may or may not branching, growing up to 3’ tall

  • Leaves alternate, or opposite, sessile

  • Flowers are in axillary umbels, vivid orange

  • Sap is not milky


Dogbane and Milkweed Differential of Shoots in the Early Spring


  • Apocynum cannabinum: Stem glabrous, solid and terete (round) in cross section, sometimes glaucous (a faint white bloom that can be rubbed off), sometimes have a reddish hue, latex is potently bitter

  • Asclepias syriaca: Stem pubescent (may or may not be easily visible- feel the stem and use a botany loup if needed), hollow and slightly squared in cross-section, green, latex is milk to sweet


Left: Dogbane shoot on the left, milkweed shoot on the right

Center: Notice milkweed's hollow stem

Right: Milkweed's pubescent stem


Shoots of other species of milkweed, as far as I know, tend to be recognizable in that they are generally much thinner, with thinner leaves. A. syriaca shoots will be about the diameter of a finger.

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