Species of the Month, August 2022: Field Thistle

Species of the Month, August 2022: Field Thistle
by Basil Conlin

I wake up early on a humid mid-July morning, my eyes opening as soon as the first robins start singing. I rush downstairs to the front garden because last night it was almost ready. This is the moment I’ve been patiently waiting 2 years for, it’s finally happening.

The Field Thistle (Cirsium discolor) I’ve grown has finally bloomed!

The blooms are delicate and glowing, subjectively unlike the introduced European thistles we’re used to; they almost glow in the morning light. They are the pinkest possible pink and are heavy with fresh nectar that has already attracted a bumblebee. Thistles are a favourite food source of many pollinators. Eastern Thistle Longhorn Bees (Melissodes desponsus), a specialist on thistle pollen, will visit and Painted Lady caterpillars will eat the abundant leaves. An ecosystem emerges.

Field Thistle in an urban Peterborough garden. Photo: Basil Conlin

Towering over me at 8ft tall and 4ft wide, this plant makes a strong impression in a small urban garden like mine. The fact that I decided to plant this species in a row of six going around the house makes the statement even bolder, resembling thorns surrounding Sleeping Beauty’s castle. The thick stems branch out repeatedly. I start counting flower buds but lose count after 105. 105 flower buds. On a single towering giant of a plant! Thorny leaves curling in the hot sun make the plants look wild, untamed. And they are.

Thistles (genus Cirsium) are a polarizing plant. On one end they represent rugged wilderness and are admired by many; a perfect choice for the official flower of Scottland and for me, a mascot for our tallgrass prairie heritage in Ontario. On the other end, they represent a landowner’s nightmare as a maligned and occasionally painful, highly invasive weed.

Bull Thistle (Cirsium vulgare) is an invasive and common species that often shows up in lawns as a basal rosette of very sharp, stiff, thorny leaves before flowering in its second year. The scientific name ‘vulgare’ is very fitting if you happen to step on one of these rosettes barefoot, ouch! Canada Thistle, also known as Creeping Thistle (Cirsium arvense) can quickly take over open areas. Despite its name, this is an introduced European invasive that can quickly spread thanks to its aggressive rhizomes. I had to do a lot of PR with my neighbours to assure them that my rare, native Field Thistle wouldn’t invade their lawns with razor-sharp weeds!

Field Thistle hosting both a Two-Spotted Bumblebee (Bombus bimaculatus) and a Bicolored Striped Sweat Bee (Agapostemon virescens). Photo: Basil Conlin

While we’re all familiar with the introduced thistles, ubiquitous and hard-to-miss plants in mid-summer, our native thistles in Ontario are more obscure and rare. The most frequently encountered species near Long Point is the Swamp Thistle (Cirsium muticum), a tall and somewhat thin-looking plant that resembles my beloved Cirsium discolor, but without significant spines on the floral bracts. Where Field Thistle loves to grow out in the hot, dry prairie and in low areas of oak savanna (a habitat that is fairly rare outside of restorations), Swamp Thistle is happy growing in wetlands throughout Ontario. It even grows in the far boreal north of Moosonee! Both species can be separated from invasive thistles by the highly contrasting white underside of the leaves.

Field Thistle is less common, favouring remnant oak savanna and prairie. It is ranked by the NHIC as an S3 species in Ontario, the unprotected equivalent to a vulnerable listing. Despite seeding readily and being a bodacious beast of a plant in the garden and in the wild, it seems that Field Thistle just can’t compete as well as its introduced, vulgare, cousins.

This seems to be the case for most of our enigmatic tallgrass prairie/savanna flora. It strikes home for me as I remember that I’m gardening on a piece of land that was a diverse prairie-savanna ecosystem around 100-150 years ago. I look across the street and see a heritage Burr Oak (around 250 years old), open-grown and stretching, a direct inhabitant of the now gone and indigenous-tended mishkodeh known to Catherine Parr Trail and other white settlers as ‘Scott’s Plains’. A place where cultural fires kept the “place at the end of the rapids” open and productive. A rolling plain dotted with pines and oaks, where one could see almost endless fields of Wild Lupine (Lupinus perennis) and Scarlet Paintbrush (Castilleja coccinea). The lupine is extirpated from Peterborough County now and the paintbrush occurs at only one small site. I wonder if a century ago if I were to stand in the same spot I’m standing, would I have seen a Karner Blue butterfly?

Field Thistle at Alderville First Nation. Photo: Basil Conlin

I will always be amazed at how something so ubiquitous, so commonplace as flowers in a field can become so rare and unheard of in only a few short generations. How our heritage can almost slip away right in front of us.

I have only encountered Field Thistle a few times in the wild, and each time it felt like I was seeing a relict of the ‘old way’. A world where the intimate beauty and reciprocity of tallgrass prairies were more abundant and accessible.

But the old world hasn’t been forgotten. The prairie isn’t dead, it’s only sleeping, and for me when I look up at the scraggly, chaotic tangle of intense pink blossoms, covered in bumblebees, in my yard that some people might not understand, this idea feels very real and possible to me.

Two-spotted Bumblebee (Bombus bimaculatus) on Field Thistle in Basil’s garden. Photo: Basil Conlin