Milkweed is a whole genus of about 140 species of herbaceous perennial flowering plants, scientifically known as Asclepias. These plants are found throughout North and South America, and many of them are cultivated as ornamentals. Its genus name “Asclepias” refers to the Greek god of medicine Asklepios.
Milkweed grows quickly to two to four feet in height. It has a narrow vertical growth habit. Most species are toxic to humans and many other species.
Most milkweeds have white latex (milky sap), but some have clear sap. This is where the name “milkweed” comes from. The leaves are simple, most commonly opposite; the blades are variously shaped but are often somewhat wavy. They have unique flowers with five united petals, pod-like fruits, and tufted seeds that aid in wind dispersal.
Flowers can be yellow, orange, red, pink, purple and white. Milkweed is best known for being the exclusive food source for the larvae of monarch butterflies. It also provides nectar for bees, wasps, and butterflies.
Milkweed produces hundreds of fluffy seeds, which are distributed widely by the wind. In fact, each milkweed seed has a parachute, or pappus, which helps it travel farther. Seeds quickly germinate and form deep and extensive root systems. Those seeds that don’t immediately germinate can remain viable for months, even in water. In addition, milkweed is tolerant of many herbicides. All of these characteristics make it a difficult weed to eradicate.
Milkweed Varieties
- Tropical milkweed (Asclepias curassavica)
- Showy milkweed (Asclepias speciosa)
- Swamp Milkweed (Asclepias Incarnata)
- Antelope horns (Asclepias asperula)
- Cedar Hill milkweed (Asclepias lanceolata)
- Oval-leaved Milkweed (Asclepias Ovalifolia)
- White Swamp Milkweed (Asclepias Perennis)
- Purple Mikweed (Asclepias Purpurascens)
- Common Milkweed (Asclepias syriaca)
- Butterfly Milkweed (Asclepias tuberosa)
- Wheel Milkweed (Asclepias Uncialis)
- Redring Milkweed (Asclepias variagata)
- Green comet milkweed (Asclepias Viridiflora)
- Green Antelopehorn (Asclepias viridis)
- Whorled milkweed (Asclepias verticillata)
- Fourleaf Milkweed (Asclepias quadrifolia)
- Welsh’s milkweed (Asclepias welshii)
- Rush milkweed (Asclepias subulata)
Description And Pictures
Tropical milkweed (Asclepias curassavica)
The tropical milkweed is native to the American tropics and has a pantropical distribution as an introduced species. The flowers are in cymes with 10-20 flowers each. They have purple or red corollas and corona lobes that are yellow or orange. Flowering occurs nearly year-round.
Unlike the milkweed species native to certain locations, tropical milkweed does not go dormant in the winter, causing non-migratory groups of butterflies to form. It’s also known for its thin stems and an open form, which makes it look best mixed with other tall plants.
Other common names include bloodflower,cotton bush, hierba de la cucaracha, Mexican butterfly weed, redhead, scarlet milkweed, and wild ipecacuanha.
Showy milkweed (Asclepias speciosa)
This is a hairy, erect perennial growing up to 47 inches in height with large, oval, blue-green leaves arranged oppositely on stalks. It is found in the western half of North America. It has a fragrant pinkish-white flowers that bloom in spherical clusters from late spring to early summer.
Showy milkweed grows up to 3 feet tall when planted in moist, well-draining soil in a sunny spot. It has a rough, weedy perennial appearance with gray-green leaves and stems that are covered in velvety hairs.
This species is not listed as a noxious weed by the federal government or any state in the United States. However, it does spread vigorously by rhizomes, so it may not be a good choice for small, formal gardens where it could overwhelm smaller plants.
Swamp Milkweed (Asclepias Incarnata)
Swamp Milkweed is commonly found in wet meadows, swamps, river bottomlands, and wet areas throughout the United States and Eastern Canada. It grows to a height of 3 to 5 feet and spreads 2 to 3 feet wide. It has narrow, lance-shaped leaves.
The plants bloom in early through mid-summer, producing small, fragrant, pink to mauve (sometimes white) colored flowers in rounded umbellate racemes. The flower color varies from darker shades of purple through soft, pinkish purple, and a white flowering form exists as well.
Antelope horns (Asclepias asperula)
The Antelope horns also known as spider milkweed, is native to the Southwestern United States and northern Mexico. This milkweed gets its name from the seed pods that resemble the horns of antelope. You can easily spot the flower clusters (technically, umbellate cymes) in open meadows.
The plant is low-growing, not exceeding 2 feet in height, and is characterized by its long, narrow leaves that fold upward from a central vein. The flowers are greenish-yellow with maroon highlights and bloom in clusters from April to June.
Asclepias asperula is divided into two subspecies:
- A. asperula. ssp. asperula
- A. asperula ssp. capricornu.
Ssp. capricornu occurs in comparatively more mesic conditions and has comparatively broader leaves, floral crowns that are more white, and a more prostrate habit. Ssp. asperula occurs in comparatively more arid conditions and has comparatively narrower leaves, floral crowns that are more purple, and a more upright habit.
Cedar Hill milkweed (Asclepias lanceolata)
Cedar Hill milkweed also referred to few-flowered milkweed is native to the coastal plain of the United States from New Jersey to Florida and Southeast Texas. It is commonly referred to as Cedar Hill milkweed, because it was first described by Dr. Eli Ives in the neighborhood of Cedar Hill in New Haven, Connecticut.
It is an upright plant that can grow between 3 and 5 feet tall. Its clusters of bright orange-red flowers that bloom in the summer months, typically from May to August. The flowers are arranged in umbels (flat-topped clusters) at the ends of the stems, with 1-3 umbels per plant. The flower hoods extend well above the stigmatic disc, and the horns are prominent and curved inward.
They call it Fewflower milkweed because it usually has 5-12 bright orange-yellow flowers adorned with a red corolla. It can be frequently found in marshes (fresh and brackish), low glades, and wet pine barrens.
Oval-leaved Milkweed (Asclepias Ovalifolia)
This lesser-known milkweed species blooms in late May to early July. The flowers are white and produced in several umbels (a cluster of flowers stalks arising from a common point). Like many other milkweed species, the oval-leaved milkweed is toxic to humans and animals if ingested in large quantities.
The plant is upright, but short, and has just a few pairs of oval leaves along the stem. The leaves are on short stalks and have no teeth along the margins. Fertilized flowers produce erect follicles (seed pods) that are covered in fine hairs and held upright.
The oval-leaved milkweed is native to prairies and savannas. It is rare in the eastern portion of its range in Illinois and Wisconsin, but more prevalent, although still uncommon, in Iowa, Minnesota, and the Dakotas. It is mostly found in remaining high quality natural areas and prefers open sun and frequent wildfire.
White Swamp Milkweed (Asclepias Perennis)