Thistle, Field

Name: Field Thistle

Botanical Name: Cirsium discolor

Form: wildflower

Parts Used: seeds

Citation: Guenther, K. (2017, January 12) Field thistle as wildlife food [Web log post.] Retrieved: readers supply the date, from http://wildfoods4wildlife.com

 Getting Started

Both Circium spp. and Carduus spp. seeds rank #41 on our Super Seeds list.

You have to really love your rehabber to collect thistle seed. Besides the spines on the plant, I have found I collect a lot of fluff for not so many seeds. But thistle is an easy to identify genus and an easy to find plant. And for goldfinch, well, it is one of their favorite foods.

Many folks can recognize the spiny thistle plants of summer field and roadside. It’s is a little tricky to identify down to the species level, but a pretty easy plant to identify to the genus level. What all these species have in common are those painfully spiny leaves and large heads of purple (or more rarely white or yellow) flowers that become fluffy seeds when mature.

Asteraceae (Aster Family)

Carduoideae (Thistle Subfamily)

Cynereae (Thistle tribe)

Circium (Genus)

OR

Carduus (Genus)

Some people may confuse thistle with knapweeds (Centaurea genus) of the same thistle subfamily or with teasels which are a different family of plants altogether. Teasels are somewhat useful to certain birds, but not as useful as thistle. Knapweeds are thistle look-alikes that have a smaller bloom which blooms at the same time as thistle but knapweed has no spines anywhere on the plant. Knapweed seeds are also eaten by birds.

In Virginia, there are many native thistle species, but as often is the case, the relative likelihood of encountering a non-native species is high. Wildlife probably prefer native species: it would stand to reason. Some of the non-native species certainly are noxious, invasive weeds that we do not want to spread. The risk of spreading non-native seeds into the larger ecosystem can be reduced if you clean the collected seed of its pappus “parachute” hairs.

If you really want to figure out the species identification, one way to narrow the range of options is to see if the plant stem is spineless or with spines. Natives in Virginia typically do not have spines on the stem.

Common name Virginia Cirsium species Origin Spines on Stems? Rare Plant Status
tall thistle C. altissimum native no Globally secure, critically imperiled in Virginia
Canada thistle C. arvense non-native no not rare
soft thistle C. carolinianum native no Globally secure, critically imperiled in Virginia
field thistle C. discolor native no- but has hairs not rare
yellow thistle C. horridulum native no yes, in some states (not Virginia)
swamp thistle C. muticum native no yes, in some states (not Virginia)
Nuttall’s thistle C. nuttallii native no Globally secure, may already be extirpated in Virginia
pasture thistle C. pumilum native no not rare
sandhill thistle C. repandum native yes Globally secure, may already be extirpated in Virginia
Virginia thistle C. virginianum native no Globally vulnerable, imperiled in Virginia
bull thistle C. vulgare non-native yes not rare
Distribution of <i>Cirsium discolor</i> (Muhl. ex Willd.) Spreng.
Field thistle range map. Range Map: USDA, NRCS. (2015). The PLANTS Database, National Plant Data Team, Greensboro, NC 27401-4901 USA. Retrieved dates on a variety of from 2015-2017 from http://plants.usda.gov

Key Features to Look For

In addition to the identification guide of your choice, here are a couple of features you should see on field thistle:

  • Very tall, well over one’s head in height
  • Has hairs, but not spines, along main stem
  • Very narrow leaves where the indentations (sinuses) of the leaf almost to touch the rib
  • Pink round flower head looks like it has a small green pineapple directly underneath it
  • Sharp spines on all leaf lobe tips

 Risks

No risks associated with animals eating seeds.

About this Species

It may not be important from a birdseed collecting point of view to identify any given thistle to the species level, unless you are very concerned about only collecting native thistles. But this native species—field thistle— really stands out as a very tall species, and towers over my head at about 8 feet.

Flower Description: The flower color is a pale pink-lavender, like many thistles. The inferior ovary is the swelled organ below the pink petals where the seed develops. If viewed from the side it looks a little like a green pineapple (to me). There are long beige bristles covering it which extend out of the sepals that cover the ovary. The topmost leaves of the stem also curl upward and hug the ovary.

Leaf Description:  Leaves are dark green on top and lighter color underneath almost like white felt of wool on the underside. The leaves are narrow and deeply incised, with spines on the end of each leaf lobe.

Notice those spines on the leaves that make collecting thistle seed a true pain.

Seed/ Fruit Size:  The cleaned seed itself (no pappus) is about 3/16 inch wide (2 mm) and 13/32 inch long (4 mm) and reminds me of a banana pepper in shape. The white pappus “parachute”or “hair”, is about ¾ inch long (20+ mm).

A single field thistle seed with pappus.
…and without the pappus.

Harvest

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
winter winter late winter early spring spring late spring early summer summer late summer early fall fall late fall
seeds x x x

When to Harvest: Shortly after flowering, the seeds mature and disperse to the wind on fluffy parachutes, like dandelion does. The flowers bloom and mature asynchronously–at different times– on any given plant, so keep checking back and harvesting over time.

An August thistle bloom.

Harvesting Seed

Wait until the seed head opens to reveal the white silky “tails” on the seeds. By now, the plant may be browning and dry.

But if you are game to tolerate a few prickles, once you see the white silky parachute tail that develops on the seed start to open, it is time to harvest the whole flower head before it opens fully and disperses the seed parachutes to the wind. If you find a stand of thistle in bloom, come back each day for a week and harvest the mature flower heads as they open. Cut or break off the mature flower head and place in a brown paper sack.  Store inside so the flower heads will dry from any moisture and continue to ripen for a couple of more days or a week.

After dry, to clean the seed out of the flower head, hold the flower head (now brown, dried sepals) in one rubber-gloved hand (to avoid the prickles)and pinch the fluffy pappus (white feathery silky fluff)  with your other hand and pull it straight out  and place it in a large bowl. Hopefully you will see the seed pull out with the pappus.

Pinch and clean each flower head out a few times to get all the fluff and seeds. If you pull out the pappus and there is no seed attached, then you can break the flower head in half after removing all the fluff and see if you can scrape out the seed that might still be lodged in the ovary.

Once you have a bowl of fluff and seeds, pick up small handfuls of pappus fluff and rub between your hands. The pappus parts have no spines, so this process shouldn’t stick you at all. The pappus will bunch up as you rub and most of the seeds will fall out. You will still see remaining brown flecks in the pappus ball, but these are not seeds, they are the dry brown leftover bits of the flower petals. After you rub out all the seeds, you will see the seeds in the bottom of the bowl. There will not be as many as you hoped for.

Ready to harvest for seed.
This is the seed head with the sepal flower base, the pappus and seed still attached in the sepal base. The plant stem and leaves have already been discarded.
Grab the white pappus hairs all at once and pull straight out from the sepals.
After discarding the sepal flower base , what remains here is the white pappus and the brown seed.
Then, continuing to hold the fluff with the seeds exposed, you can often use your finger to shear off the small dark seeds just by rubbing perpendicular to the pappus. Or just rub small handfuls of the fluff together and the seeds will fall to the bottom of the bowl.
You see what is left now, the pappus at the top to discard, and seed to keep at the bottom.
Done!

Other Thistle Species

You may even see white thistles!
This giant domestic species of thistle is in the garden of the restaurant Harvest Table, which is author Barbara Kingsolver’s family’s restaurant in Meadowview, VA.

Rare Species in Virginia

Do you live in one of these Virginia counties? If so, be aware that there are some species near you that may be threatened or endangered. Do more research to make sure you are identifying your target species correctly and not harvesting a threatened species!

County in Virginia Species Alert
Arlington tall thistle Globally secure, critically imperiled in Virginia
Botetourt tall thistle Globally secure, critically imperiled in Virginia
Brunswick Virginia thistle Globally vulnerable, imperiled in Virginia
Charles City Virginia thistle Globally vulnerable, imperiled in Virginia
Chesterfield Virginia thistle Globally vulnerable, imperiled in Virginia
Dinwiddie Virginia thistle Globally vulnerable, imperiled in Virginia
Fairfax tall thistle Globally secure, critically imperiled in Virginia
Fairfax soft thistle Globally secure, critically imperiled in Virginia
Franklin soft thistle Globally secure, critically imperiled in Virginia
Frederick tall thistle Globally secure, critically imperiled in Virginia
Greensville Virginia thistle Globally vulnerable, imperiled in Virginia
Halifax soft thistle Globally secure, critically imperiled in Virginia
Henrico Virginia thistle Globally vulnerable, imperiled in Virginia
Henrico tall thistle Globally secure, critically imperiled in Virginia
Prince George Virginia thistle Globally vulnerable, imperiled in Virginia
Shenandoah tall thistle Globally secure, critically imperiled in Virginia
Southampton Nuttall’s thistle Globally secure, may already be extirpated in Virginia
Southampton sandhill thistle Globally secure, may already be extirpated in Virginia
Sussex Virginia thistle Globally vulnerable, imperiled in Virginia
Virginia Beach Nuttall’s thistle Globally secure, may already be extirpated in Virginia

 

Feed Field Thistle to:

thistle

(Carduus spp.)

seeds

Deer, White-tailed

Odocoileus virginianus

Mouse, Common White-footed

Peromyscus leucopus

Mouse, Deer

Peromyscus maniculatus nubiterre

Vole

various spp.

Vole, Pine

Microtus pinetorum

Vole, Red-backed

Myodes spp., Clethrionomys spp.

Goldfinch, American

Carduelis tristis

strong preference

Bunting, Indigo

Passerina cyanea

Finch, House

Carpodacus mexicanus

Junco, Dark-eyed

Junco hyemalis

Pipit, American

Anthus rubescens

Redpoll, Common

Carduelis flammea

Siskin, Pine

Carduelis pinus

Book References:

Martin, A.C., Zim, H.S., Nelson, A.L. (1951). American Wildlife and Plants: A Guide to Wildlife Food Habits. New York: Dover Publications.

Scott, M. (2013). Songbird Diet Index. National Wildlife Rehabilitators Association, St. Cloud, MN.

Townsend, J. F. (2015, April) Rare Plants Natural Heritage Technical Report 15-10. (Unpublished Report) Richmond, Virginia: Virginia Department of Conservation and Recreation, Division of Natural Heritage.

On-line Resources:

USDA, NRCS. 2015. The PLANTS Database (http://plants.usda.gov, 4 January 2016). National Plant Data Team, Greensboro, NC 27401-4901 USA.

Virginia Botanical Associates. (Accessed January 2016). Digital Atlas of the Virginia Flora (http://www.vaplantatlas.org). c/o Virginia Botanical Associates, Blacksburg.

Zouhar, Kris. 2002. Cirsium vulgare. In: Fire Effects Information System, Online].
U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer).
Available: http://www.fs.fed.us/database/feis/plants/forb/cirvul/all.html [2016, December 4].

Zouhar, Kris 2001. Cirsium arvense. In: Fire Effects Information System, [Online].
U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer).
Available: http://www.fs.fed.us/database/feis/plants/forb/cirvul/all.html [2016, December 4].