A Tough Stemmed Plant With Thistle Like Flowers: Knowing the names of these three annual thistles is helpful because they can be found all around northern California. However, they have the potential to develop on a variety of other types of land, including rangeland, pasture, and natural regions. These seeds germinate and form rosettes during the winter, before Bursting into purple flowers in the spring.
Although these species are native to southern Europe and southwest Asia, they are also found throughout the Middle East. The ability to coexist with human agriculture was something they ‘learned’ early on. If you’re about to kill those thistles, think twice:
Identifying a Thistle: Clackamas County property owners deal with thistles on a regular basis. There are a number of thistles that can quickly take over the land. However, did you know that at least four species of thistles endemic to western Oregon are not only non-invasive? It’s a win-win situation for both the health of our working fields and natural regions when native thistles are allowed to grow in abundance.
You should care about Native Thistles: These wildflowers serve as vital habitats and food for local wildlife. Bees, butterflies, and other pollinators depend on the nectar and pollen of native thistles for nutrition. Many insects and songbirds eat the leaves, stems, flowers, and seeds of thistles. A year-round supply of nectar for pollinators can boost the yields of many-valued crops.
Non-native thistles are less likely to take over a region if native thistles are present. A robust population of beneficial insects can be supported by native thistles, which will also eat non-native thistles. The native thistles in our area do not aggressively displace other plants and maintain a healthy balance with them. Because they have spines or are deemed “weeds,” native thistles are either intentionally or unintentionally killed. Regardless of their benefits, thistles are either intentionally or unintentionally eliminated. As a result, several native thistles are at risk of extinction in our region.
Non-Native Thistles: A Serious Threat
When thistles that are not native to a region take over a field or pasture, they have the potential to wreak havoc on farming and grazing operations, displacing native plants and lowering agricultural yields. Controlling them also takes a lot of effort and money. When it comes to controlling thistles, it might be difficult to tell them apart because they all seem the same. We’re here to assist you.
Characteristics of the Thistle
Annual, biennial or perennial thistles belong to the sunflower (Asteraceae) family. The flower heads of true thistles are often pink-purple and encircled by bracts that are normally spiky, with spines along the leaf margins. You can tell if your thistle is native or not by asking yourself a few of the following questions:
- Is the thistle’s stem covered in spines? Is thistle (a YES denotes Italian thistle, slender flower, Scottish, or bull thistle) a plant?
- Triangular, firm, and spine-tipped bracts are common. Italian thistle, or slender flower thistle, if you say “yes”
- What kind of texture do the bracts have? (Milk thistle is shown if the answer is YES)
- Rhizomatous: Are the roots? (a YES means Canada thistle if the answer is YES)
- You may have a native thistle if you answered “NO” to all of the following questions!
Native Thistle: Clustered thistle (Cirsium Brevistylum)/Indian thistle/Short-styled thistle:
- Annuals, biennials, and perennials with a limited lifespan
- Branched/clustered and fuzzier near the top, the stems are largely unbranched and fuzzy.
- “Cobwebby” flower heads
- Small white stalks (the “styles”) emerge out of individual flower tubes less than 1 mm in diameter, giving the flower heads a red-purple hue.
- Long and tapering bracts surround the flower heads.
- With the topmost leaves protruding over the flower head, the leaves point upwards
- Weakly spined leaves with hairy undersides and shallowly lobed blades (sometimes slightly woolly on the top)
- Plants can reach heights of up to seven feet.
Cirsium edule, an edible thistle
Short-lived perennials and biennials: However, this plant has more branched branches and more spiky leaves, making it look similar to the clustered thistle.
- The flower’s cobwebby head dangles from the immature plants.
- Flower tubes come in a variety of lengths, from 3 to 8 mm.
- Foliage is covered in a thick layer of hair, particularly in and around the midrib.
- The base leaves can grow to a length of 15 inches.
- The plant can reach a height of 9 feet.
- Thistle with few leaves (Cirsium remotifolium)
- Plants that are either biennials or short-lived perennials exhibit wide individual variety.
- Woolly or smooth stems can be found on plants.
- The upper half of the plant is sparsely branched and has weak spines.
- Only mildly cobwebby, the flower heads can range in color from white to purple.
- Spiny bracts have papery borders that may be a little fringed, but they are otherwise smooth.
- The undersides of the leaves are covered in hairs, and the lobes are spiky.
- A leaf’s stalk may be short, or it may be attached to the stem without one.
- The plant can reach a height of 6 feet.
Thistle with wavy leaves (Cirsium undulatum)
Perennial
- The upper half of the stems are branching, and the white hairs that cover it are matted.
- Single, pale lavender to white and up to 2 inches wide flower heads are common.
- In addition to their spiney tips, bracts feature a sticky midrib.
- All sides of the leaves are covered in hair.
- The golden spines on the leaf edges have shallow, wavy lobes.
- The plant can reach a height of four feet.
Invasive Non-native Thistles
Cirsium vulgare (bull thistle): See our weed profile for more information on this common yet somewhat invasive species in Clackamas County.
Biennial
- The stems are thick, leafy, branching, and fuzzy in appearance.
- There are many spiky spine-tipped bracts on the big, rose to purple flower heads
- The end lobe is longer than the other lobes, and all of the prickles on the leaves are yellow.
- The underside of the leaves is hairy.
- The “wings” of leaves may be clearly seen (flat projections extending down the stem)
- The plant can reach a height of 6.5 feet.
- Thistle of Canada (Cirsium arvense)
- Clackamas County has a lot of it, and it’s a very invasive weed.
- Underground stems allow this perennial to spread.
Hairy stems and thin, ridged leaves
- Purple, little (less than 2 cm), and grouped flower heads
- Largely triangular in shape, bracts have few or no spines.
- The tiny, lobed leaves contain yellowish prickles on the margins.
- The plant can reach a height of 6.5 feet.
- It is a wonderful milk thistle to behold (Silybum marianum)
- Invasive and rare, yet prevalent in Clackamas County, read our Weed Profile or Best Management Practices for more information on this invasive species.
Every two years (sometimes annual)
- The upper half of the stems are ridged and branching, with scant hairs.
- This plant has huge, purple flower heads (up to 2 inches across).
- Stout, jagged, and extremely pointy bracts are 1-2 inches in length.
- The dark green leaves have a unique white marbling on the underside of each one.
- Base leaves can grow to a length of up to 20 inches.
- The plant can reach a height of 8 feet.
- Carduus hydrocephalus, the Italian plumeless thistle, and the slender flower thistle (Carduus tenuiflorus)
- In Clackamas County, it is not known to exist.
- Species that appear like each other yet are yearly
- Branches point upward from fuzzy stems with a lot of spiny wings.
It grows in spiny clusters of 2 to 5 (on Italian) and 5-20 flower heads that are pink-purple and tiny (0.5 inches broad) (on the slender flowers)
- The bracts of Italian thistle are hairy and spiky, and the hairs on the bracts are stiff and pointed.
- The underside of the leaves is covered in fine hairs and the lobes are topped by spines.
- The plant can reach a height of six feet.
- Thistle of the Scots (Onopordum acanthium)
- In Clackamas County, it is not known to exist.
Every two years (sometimes annual or short-lived perennial)
- The entire plant has a bluish-grey look and is extremely branching.
- The stem is made of wood and has a lot of spines (flat-leaf projections extend down the stem)
- Flowers have purple heads that are 1 to 3 inches across.
- Flat, pale orange spines adorn the tips of the bracts.
- Triangular lobes, spines, and silvery hairs cover the leaves, which can grow up to a foot long.
- The plant can reach a height of 8 feet.
Want to go further: Many more species have been left out of this discussion, either because they are not known to occur in western Oregon or because they are not technically considered “thistles.” In addition to that, this post is already too long. These “thistle-like” analogs can be found by clicking on the links below.
