Thursday, February 25, 2021

Milky sap

By Larry Cornelis – President, Sydenham Field Naturalists

It’s the milky sap that gives this genus (Asclepias) of plants their common name, ‘Milkweed’.

Larry Cornelis Photo

We have seven species of milkweed locally including; butterfly milkweed (Asclepias tuberosa), common milkweed (A syriaca), green milkweed (A viridiflora), poke milkweed (A exaltata), purple milkweed (A purpurescens), Sullivant’s milkweed, (A sullivantii) and last but not least, swamp milkweed (A incarnata).

There are two other species, A hirtella and A verticillate, growing in Southern Ontario, both in Essex county.

Milkweeds are wonderful long-lived herbaceous perennials with high ecological values.

The scientific name Asclepias is for the Greek God of healing (Asclepius) because of the many traditional and folk medicines of milkweeds.

School children once collected milkweed seed pods (during the second World War) to fill life jackets with the silky fluff that is attached to the seeds.

Recently the milkweed silk is used as a hypoallergenic stuffing for comforters and pillows.

Growing and supplying this milkweed silk is mostly a Quebec based industry.

Children are also growing milkweed plants at school to help save the Monarch butterfly.

Milkweed is the only host plant for monarch caterpillars.

They cannot eat anything else.

No milkweeds, no monarchs.

Thankfully, in Ontario, milkweeds were removed from the provincial noxious weed list and we are permitted to grow it in our gardens and let it grow wild in rural landscapes.

As stated earlier, milkweeds are wonderful plants full of natural values.

They have very showy, interesting and complex flowers.

They are similar to orchid flowers in complexity.

There are five petals reflexed backwards revealing fused stamen filaments and styles which are surrounded by a five membered corona.

The corona is made up of five paired hood and horn structures with the hood acting like a sheath for the innerhorn.

Unlike most flowers, milkweed flowers don’t have pollen grains.

They have structures called pollinaria.

Insects looking for a milkweed’s plentiful nectar have a tough job reaching it and sometimes get stuck in the slits between the hoods of the flowers.

As they struggle to pull away, they get the pollinaria on them and take it to the next flower.

Milkweeds are one of the best sources of nectar for pollinating insects of all types.

Depending on the species, the flowers come in a range of colours including white, yellow, orange, pink and purple.

On close inspection, most people are very surprised by the beauty and fragrance of milkweed flowers.

In your garden, during the summer when the flowers are blooming, milkweeds will be a showcase of activity with butterflies, moths, bees and other pollinators.

Having milkweeds in your garden is great if you’re into nature photography.

Nectar seeking butterflies and bees pose nicely for photos.

Larry Cornelis Photo

And you can get close to busy bees without worry of getting stung.

Milkweeds are a must in the pollinator/butterfly garden and an important genus for large scale restoration projects.

They are easy to grow from seed and you can either direct sow outside in the fall or grow some
inside in March to plant out in early May.

Growing even a small patch of several plants will support monarchs and other pollinators.

Common milkweed is a bit aggressive for the garden, spreading by rhizomes.

The rest are clump forming well-behaved perennials.

Poke milkweed is shade tolerant and the others all thrive in full sun.

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