Invasive SpeciesBull thistle

Cirsium vulgare
FOUND by antheriault
E. Waterboro
Not Yet Reviewed by Expert
Quality checked by pparent
Peer reviewed by pparent
Field Notes
In September of 2011 we were at the pond site at Massabesic Middle School trying to locate and identify Purple Loosestrife. During that investigation we did not locate any Purple Loosestrife other then the single plant previously identified by a class in the spring of 2010. While we were at the pond site we located a plant that we had never seen before. Our mission is to study and identify the plant. The first time we went out to study the plant the day was sunny, with few clouds in the sky. The temperature was recorded as 23.9ºC, with 60% humidity, wind speed of 0 mph, and a dew point of 16.4ºC. The plant is growing in a pathway along the edge of the pond. The second observation of the plant was to take photographs and measurements, this took place after a very hard frost had occurred the previous night as can be seen in the photographic evidence. The plant is a young plant. It's leaves are approximately 7-8mm wide and 36mm long. The lobes of the leaves aren't fully developed at this time but the thorns at the tips can be seen. The surfaces of the leaves are hairy and slightly fuzzy. The stem also has thorns growing on it. It's stem is woody, like a stick as shown in the evidence photo. This plants stem was approximately 115mm tall and approximately 3mm in diameter approximately the diameter of a #2 pencil. The flower on this plant had gone by and died off at the time of this investigation but left behind a round gumdrop shaped seed pod with thorns protruding. Inside the seed pod revealed hair like seeds slightly white in color. Based on our photographs and investigation we have identified this plant to be Cirsium Vulgare, also known as Bull Thistle. Based on research it is known that Bull Thistle is invasive. My question is how far will the Bull Thistle spread on the Massabesic Middle School Campus, if at all?
A sketch of our study site.
Supporting Evidence
Photo of my evidence.
The leaves on this plant are young and not completely developed at this time so the lobes are not clearly defined. The measurements of our leaves were 7-8mm wide and approximately 36mm long. We observed the thorns growing on the points of the leaves where the lobes are developing. The surfaces of the leaves were hairy/fuzzy. The thorns and surface areas of the leaves are the same as Bull Thistle. During our investigation we noted a partial larger leaf on the plant that had more developed lobes and were the same as Bull Thistle leaves. We found pictures of a young Bull Thistle plant and the size, shape, and features of that plant were the same as our plant.
Photo of my evidence.
The stem of our plant is woody like a stick. Our plants stem was approximately 115mm tall and 3mm in diameter. We observed thorns growing on our stem, which has the same characteristics as Bull Thistle. The leaf arrangement on the stem was that of a whorled pattern, which is also a characteristic of Bull Thistle.
Photo of my evidence.
At the time of our investigation the flower had died off and left behind a round drop shaped seedpod. Observations of the pod showed thorns growing from the pod. Inside the pod were hairlike seeds. These seeds are consistent with the seeds that of Bull Thistle as well as the shape of the seed pod and left over dead flower.
Species Observation: Species Looked For
Did you find it?: 
I think I found it
Scientific name:
Cirsium vulgare
Common name:
Bull thistle
Count of individuals: 
Less than 1/4 covered
Flower (plants)
Sampling method: 
Just looking around
Photo of our sampling method.
Place Studied
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Map this species
N 43.581942 °
W -70.702802 °
Observation Site Information
A photo of our study site.
Freshwater - By water's edge
Trip Information
Pond Area Biodiversity Study
Trip date: 
Tue, 2011-10-11 08:13
Town or city: 
E. Waterboro
Type of investigation: 
Species and Habitat Survey
Habitat Observations
Species diversity: 
40 different species
Evidence of vectors: 
Paved road
Walking trail
Recent disturbance
Tree canopy cover: 
Open to 1/4 covered
Soil moisture: 


The plant is a biennial plant. It says it has a 2 year life cycle flowering and setting seed in the second year. Seeds are short-lived on the soil surface but can persist for many years when they are buried. Seed germination generally occurs in the fall and spring. Will just have to keep checking back I guess to see if it's in an off year.

I returned to the study site this morning to check out my plant. My plant is no longer in the walkway where I origninally spotted it. Not sure if it got pulled up or just died off. I will continue to check the area periodically so if by chance it returns. One thing to note as well, I had the same plant growing at home and for the past 2 summer seasons it has not returned which leads me to another question, why are these plants not returning?

Do you know anything about your plant's life cycle? Is it an annual, a perennial, a self-seeder, a 2-year life cycler? Knowing a bit more about it, even from a quick scan in a book or a quick internet search, might help you uncover the why...

It certainly is curious!


So my Bull Thistle saga continues. We will be going out to the study site this week and I am hoping to find my plant. I will update my progress.

I wonder what you'll find!


Have returned to the study site now that we are back at school and much to my dismay the plant is not there. So that now throws a monkey wrench into my thinking yet again as my research has shown that Bull Thistle is Biannual. So are we in the year that it won't grow, did someone pull my plant, or did it just die and I will never really get my answer. And so my investigation continues for yet another year.

They don't tell you in school how much patience science requires!

I just did a little reading about biennial thistles (your comment made me curious). In the first year, they overwinter as a rosette, which would look like the plant that you saw last year. If your plant had survived, it would have grown into a tall, flowering plant, releasing its seeds before dying off in the cold of this fall. (You probably knew that, but I had to spell out the chronology).

Did you see any dead thistles around? Or just plain old nothing? And have you asked the folks who tend the fields and lawns if they sprayed or did anything to treat weeds? You might find your answer!

I'm going to keep following this saga! Please post what you learn!

Hi antheriault,

I'm not a thistle expert, but I found some website that might help you. - this site seemed to be a pretty user-friendly tool for identifying thistles. You need to be really dubious, however, about whether their classification of "exotic" thistles applies to you. The site seems to be associated with a group in the Midwest. Their exotics/ invasives may not be the same as Maine's. The guide should help you identify the species of thistle you saw. Then you'll have to do a little more research to find out whether that species is invasive in Maine. - this site doesn't provide the dichotomous key like structure of the first one, but it does give quick descriptions of common thistle species. It might prove helpful.

In any case, I strongly encourage you to make another Vital Signs observation of the plant in question, especially once it has more mature leaves (it might be too long to wait until it has a flower, but that would really help identification). I'm going to subscribe to your posts so I am sure to see your next species observation contribution to this site!

Thanks for being curious and looking again and again at your plant!


I have been out to the study site over the past 2 weeks and am now questioning my identification of this plant as Bull Thistle. The plant is not showing the same characteristics as a young Bull Thistle plant. The leaves on this plant are not showing the same lobe development as a young Bull Thistle would be at this time of the year. At this time there is no flower growth to help with this identification.

Great photos, antheriault!

I'm no expert at all in thistles, but I can still really appreciate the thoroughness of your field notes! Well done.

Have you seen more of this thistle on the campus since your last observation? Do you have plans to go out and look more this spring?

I hope you do!