Frequently encountered types of milkweed found in Canada
Common milkweed (Asclepias syriaca)
Found in SK, MB, ON, QC, NB, NS, PE
Description: Grows up to 2.5m tall, most often found in sunny open areas, such as pastures, meadows, roadsides. Has wide, oval-shaped leaves up to 25cm long with a noticeable central vein and smaller veins running toward edges. Leaves are smooth on top, velvety texture on underside. Plant does not have branches except near the top where umbels of small flowers form in round clusters up to 10cm diameter. Stems and leaves release a milky-white sap when broken. Flowers are pinkish-purple, pleasant smelling, highly attractive to many species of insects. Plant blooms for up to 6 weeks in early to mid-summer. After blooming, seed pods develop, between 6-12cm in length, with prickly exteriors. When seedpods mature, they crack open to reveal large clusters of small brown-black seeds with white, silky tufts that are transported by wind.
Swamp milkweed (Asclepias incarnata)
Found in MB, ON, QC, NB, NS, PE
Description: Grows up to 1.5m tall, though height can vary considerably. Most often found growing in full sun or partial shade in moist or damp soils, such as along lakes, rivers, swamps, or drainage ditches. Does not grow in areas that are typically hot and dry. Unlike common milkweed, the central stem may branch. Leaves can be up to 15cm in length (but are often shorter), are much narrower (1-4cm width) than common milkweed, and taper to a sharper point. Stems and leaves release a milky-white sap when broken. Plant blooms for approximately 4 weeks in mid- to late summer. Round clusters of light pink flowers grow near top of plant. The flower colours may vary from near white to purplish, and are pleasant smelling. Seed pods have a smooth exterior texture (unlike common milkweed) and ripen in fall to reveal small seeds with white silk attachments common to all milkweeds. From a distance, Joe Pye weed may be mistaken in late summer for swamp milkweed (see description below).
Butterfly weed (Asclepias tuberosa)
Found in ON, QC
Description: Grows up to 1m in height but is often smaller. Most often found in dry, sunny locations with sandy or gravelly soil. Has hairy stems and narrow, oval leaves that taper to a point, 5–12 cm long and 2–3 cm wide. Easily distinguished from other milkweed species by its large clusters of bright orange (or orangey-yellow) flowers that bloom from late spring to early fall. Develops pods of small seeds with silk attachments common to all milkweeds, but sap is clear, not milky white as in other species.
Showy milkweed (Asclepias speciosa)
Found in BC, AB, SK, MB
Description: Grows up to 1.75m in height but may be much smaller. Can grow in a variety of habitats, but most often found where water is regularly available, such as along streams and rivers, or near depressions where water collects. Grey-green oval leaves taper to a point, are 6-12 cm in length. Leaves are narrow on young plants, and widen with age. Most easily distinguished from other milkweeds by its large loose clusters of star-shaped flowers, pink to purplish in colour. Develops pods of small seeds with silk attachments common to all milkweeds. Stems and leaves release a milky-white sap when broken.
Other milkweed species are occasionally encountered in Canada, typically ones that are more common in the US. Some may have escaped from home gardens. If observed, record as “other” and enter a note and photo.
Dwarf milkweed (Asclepias ovalifolia). External link: http://www.arkive.org/dwarf-milkweed/asclepias-ovalifolia/
Green milkweed (Asclepias viridiflora). External link: https://plants.usda.gov/plantguide/pdf/pg_asvi2.pdf
Whorled milkweed (Asclepias verticillata). External link: https://www.wildflower.org/plants/result.php?id_plant=asve
Joe Pye Weed (genus Eutrochium) = not a milkweed
Description: Joe Pye Weed is the common name of various species of tall, upstanding perennial plants with leaves that emerge from a central stem. These plants are related to sunflowers, but from a distance, may in late summer be mistaken for swamp milkweed because of the clusters of purple-pink flowers at the top of their stems. Also, Joe Pye Weed grows in moist soils and is often found growing in the same areas as milkweeds. The most common varieties of Joe Pye Weed grow much taller (>2.25m), and grow in more dense, thicket-like clumps than do milkweeds. Leaves of Joe Pye Weed are long (<25cm), spear-shaped, dark green and coarsely-serrated, growing in whorls of 3-4 from a central stem. The stems/leaves do not release the milky-white sap characteristic of milkweed. The most telltale sign is that Joe Pye Weeds do not form seed pods. Joe Pye is a beautiful, native, perennial plant with flowers that attract lots of butterflies (including adult monarchs) but its leaves are not typically used by monarchs for laying eggs.
(in order of appearance on this page):
- Common milkweed = Robert McLeman; Diana Troya/Ontario Nature
- Swamp milkweed = S & A Wasowski/Lady Bird Johnson Wildflower Center; Liz Wylie
- Butterfly weed = both images UMass Amherst Extension program
- Showy milkweed = J. Hixson, Fran Cox/Lady Bird Johnson Wildflower Center
- Joe Pye Weed = Robert McLeman