What are Milkweeds?
Milkweeds are soft-stemmed plants that die to ground level at the end of each growing season but grow back from the roots the next spring. Most milkweeds have leaves in pairs or in whorls of four and sap that is white and milky. They grow in a variety of habitats.
Milkweed flowers develop in a cluster at the stem tip or in the leaf axils in the upper part of the plant. Color varies with the species, but varieties include white, pink, red, orange, green, red-purple and purple-pink flowers. The flowers are often described as having an hourglass shape. Each flower has five petals and five sepals that bend downward and a five-parted cup that supports five horns and hoods.
The milkweed fruit is a pod that contains seeds attached to floss. Seeds with floss are easily blown by wind. There is one species of milkweed in the state, though, the white swamp milkweed (Asclepias perennis), that uses water to disperse its seeds, and those seeds do not have floss.
How Many Types of Milkweeds Grow in Illinois?
Twenty-four species of milkweeds are found in Illinois.
How are Pollinators Important to Milkweeds?
Plant pollen contains male reproductive cells. For new plants to be produced, pollen must reach the female reproductive cells. Some plants use wind, water or gravity to move pollen. Other plants need the help of animals to take the pollen where it needs to go. Animals that move pollen are called pollinators. Milkweed plants need animals to move their pollen. Most milkweed pollinators are insects.
Pollinators don’t really mean to move pollen for the milkweeds. They visit milkweed plants to drink nectar. Nectar is a sweet solution produced by flowers to attract pollinators. When an insect visits a milkweed flower to drink nectar, its leg, antennae or bristles can slip into the slit in the flower where the pollen is stored. The pollen-containing structure clips onto the insect part. When the insect pulls away from the flower, this pollen packet goes, too. The same insect body part may slip inside a slit in the flower column of a different flower. If the pollen packet is placed precisely where it needs to be, that flower will be pollinated. If the pollen packet is not deposited in the exact position required, fertilization will not occur. This complicated arrangement may be the reason that milkweeds produce so few fruits.
Pollinator populations are declining. As their numbers continue to decrease, the amount of seeds from milkweeds will also be smaller, leading to fewer milkweed plants, fewer milkweed flowers and less pollen and nectar for pollinators.
How are Milkweeds Important to Pollinators?
Pollinators visit milkweed flowers for their nectar. They eat some of the nectar, and some of them also use it to feed their young. See the next section, too, for more information.
Why are Milkweeds Important to Monarch Butterflies?
A close relationship exists between monarch butterflies (Danaus plexippus) and milkweed plants. Monarchs have a life cycle that includes four stages: egg; larva; pupa; and adult. Monarch larvae feed only on milkweed plants. If there is no milkweed, there will be no monarchs. Female monarchs usually lay their eggs only on milkweed plants so that the larvae will have a food source when they hatch from the egg.
What Can You Do to Help Milkweeds?
As of 2016, five species of milkweeds are listed as endangered in Illinois with one of those species also listed as threatened federally. Milkweed populations have declined rapidly in North America over the past 20 years. What can you do to help milkweeds?
• Plant a pollinator garden that has a variety of native plants, including milkweeds. You will be helping milkweeds and pollinators.
• Plant a butterfly garden that features milkweeds. A butterfly garden provides food and shelter for all stages of butterfly life.
• Tell others about why they should plant milkweeds, and why they should not kill milkweeds.
What Else Should I Know about Milkweeds?
Milkweed plants contain poisonous chemicals that can affect birds and mammals if they eat the plants. A few animal species have adapted to eating milkweeds, though, and thrive on them. For example, monarch butterfly larvae feed only on milkweeds. The poisons build up in the body of the larval monarch and are retained by the monarch in its transformation to the adult. To many predators, the monarch larva and adult taste bad, so they don’t eat them.