“Not all that bristles is bad: in defense of thistles”


Thistles are plants that are well-known but not well-loved, at least by humans. Admittedly, they don’t often make the best impression on us thin-skinned, hairless apes. We’re just trying to go for a walk and enjoy nature. We already have to deal with poison ivy and ticks, and now we have to watch for plants with tiny little knives on the end of their leaves? C’mon!

Our disdain for these plants probably also has to do with the agricultural roots most of us have. Certain thistle species get into ag fields, and no way are we pulling those things by hand. Even the Bible suggests they are a curse, complements of Adam and Eve’s transgression (Gen. 3:17-18).

The most abundant thistle on the landscape is the poorly-named “Canada” or Field Thistle (Cirsium arvense). It is an invasive species, which means it is both non-native to this continent and causes significant ecological and economic harm. By Indiana law, it is also considered a noxious plant and landowners are legally obligated to take steps to control it (as we do here). It is a stubborn perennial plant that you don’t want in your ag field or your prairie planting. It blooms early, in June. Bull Thistles (Cirsium vulgare) are another common non-native thistle found in our pastures.

But just like those of us who come off as a like “prickly” on first encounter, we should give thistles another chance. There are several native thistles that are “well-behaved,” mixing in easily with other native grasses and wildflowers, and not a weedy problem within agricultural systems.

Pasture Thistle (Cirsium discolor) towards over neighboring plants, loaded with blooms.

Mostly importantly, native thistles are absolute magnets for pollinators, everything from showy butterflies to tiny native bees. Females of the long-horned bee species Melissodes desponsa are oligolectic on thistle pollen, meaning that their larva will not develop on any pollen unless it is a Cirsium thistle species! When thistles disappear, so does this bee species.

On the left is Swamp Thistle (Cirsium muticum), fighting it’s way up through a thick stand of hybrid cattail. I would like to think our prescribed fires have helped remove enough thatch to let a few more of these plants grow and seed.

Tall Thistle (Cirsium altissiumum) is an oak savanna species. Swamp Thistle (Cirsium muticum) has a beautiful deep-purple flower and is found in wetlands, including the fringes of Lake Galbraith. Pitcher’s Thistle (Cirsium pitcheri) is a federally-threatened plant found only on the sand dunes around Lake Michigan.

Bees and Swallowtails are both fans of Pasture Thistle.

But probably my favorite species, which is now in bloom in many of the roadsides in western Marshall county, is Pasture Thistle (Cirsium discolor). It hosts a bright pink (and sometimes white) bloom, nodding high in the breeze. I never fail to find it crawling with pollinators chowing down on the banquet of nectar and pollen. The two year-old plant dies after flowering (it’s biennial), but sprouts easily from seed.

I saw my first white-flowered variant of Pasture Thistle along 9C Road in August 2016.

(You can browse more about all these Cirsium species at the U. of Michigan database).

Neither of the major invasive thistles (Bull & Field Thistle) have this definitive white underside of the leaf, like this Pasture Thistle.

With all these redeeming qualities of beauty and function, surely now you can understand why they bear spikes. They are are an obvious defense against leaf-eating animals. You wouldn’t want to be constantly nibbled on, now would you? See, deep down, thistles are sensitive, reasonable plants on the inside, just making their way in the world. You just need to get to know them.


This post was inspired by Chris Helzer‘s great thistle post from 2015. He also created this great printable/shareable icon to spread the thistle love:

https://theprairieecologist.files.wordpress.com/2015/08/thistlefanclub.png?w=800

2 Replies to ““Not all that bristles is bad: in defense of thistles””

  1. Karen Thada

    Great post, Adam. Thanks for enlightening me about native thistles! Always dreaded those Canadian thistle patches when walking soybeans. Wore gloves, of course!

    Reply
  2. Sr. Linda Volk

    Thistles get a bad rap even in the Scriptures

    Turn to the epistle
    in your liturgical missal
    and this’ll make you whistle.

    False idols are rewarded with thistles
    (obviously not the pasture thistle).
    Also the high places of Aven, the sin of Israel, will be destroyed;
    thorn and thistle will grow on their altars. Hosea 10:8
    (Talk about invasive!)

    False prophets bear nothing but thistle and dismissal.
    “You will know them by their fruits.
    Grapes are not gathered from thorn bushes nor figs from thistles, are they?” Matthew 7:16
    I’d imagine it makes a native thistle bristle
    To be rated below the prickly sisal.

    But let’s remember it is memorialized in another “good book”.
    “He sprang to his sleigh, to his team gave a whistle,
    And away they all flew, like the down of a thistle.”

    Reply

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