Nature’s Notebook

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Photo for species Cirsium_occidentale

Thistles are members of the Sunflower family. This species is native in Western North America and is not considered a problematic weed unlike many other thistles. The long tangled hairs on the flower head resemble a cobweb. The nectar provides an important food source for visiting insects and hummingbirds.

Photo Credit:
© Wing-Chi Poon via Wikimedia Commons

Cirsium occidentale

cobwebby thistle
What does this species look like?
What does this species look like?: 

This species is a biennial; it lives for only two years. The first year it has a rosette form and in the second year it produces one flowering stem to reproduce before dying. This species is variable in form; it can have a short clumpy form in some regions (such as the California coast) or be up to 3 meters tall on other regions.  The spiny lobed leaves are hairy and grey-green to white in color. The spherical flower heads can be red, white, or purple and can be up to 8 centimeters in diameter.

Cirsium occidentale is found in a wide range of habitats including open woodlands, valleys, and deserts at elevations less than 3600 meters.

Where is this species found?
States & Provinces: 
CA, NV, OR
Which phenophases should I observe?
Leaves

Do you see...?

Initial growth
New growth of the plant is visible after a period of no growth (winter or drought), either from above-ground buds with green tips, or new green or white shoots breaking through the soil surface. Growth is considered "initial" on each bud or shoot until the first leaf has fully unfolded. For seedlings, "initial" growth includes the presence of the one or two small, round or elongated leaves (cotyledons) before the first true leaf has unfolded.

Leaves
One or more live, fully unfolded leaves are visible on the plant. For seedlings, consider only true leaves and do not count the one or two small, round or elongated leaves (cotyledons) that are found on the stem almost immediately after the seedling germinates. Do not include fully dried or dead leaves.

Flowers

Do you see...?

Flowers or flower buds
One or more fresh open or unopened flowers or flower buds are visible on the plant. Include flower buds or inflorescences that are swelling or expanding, but do not include those that are tightly closed and not actively growing (dormant). Also do not include wilted or dried flowers.

How many flowers and flower buds are present? For species in which individual flowers are clustered in flower heads, spikes or catkins (inflorescences), simply estimate the number of flower heads, spikes or catkins and not the number of individual flowers.

Less than 3;3 to 10;11 to 100;101 to 1,000;More than 1,000

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Open flowers
One or more open, fresh flowers are visible on the plant. Flowers are considered "open" when the reproductive parts (male stamens or female pistils) are visible between or within unfolded or open flower parts (petals, floral tubes or sepals). Do not include wilted or dried flowers.

What percentage of all fresh flowers (buds plus unopened plus open) on the plant are open? For species in which individual flowers are clustered in flower heads, spikes or catkins (inflorescences), estimate the percentage of all individual flowers that are open.

Less than 5%;5-24%;25-49%;50-74%;75-94%;95% or more

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Fruits

Do you see...?

Fruits
One or more fruits are visible on the plant. For Cirsium occidentale, the fruit is very tiny and seed-like and is crowded into a large spent flower head. The seed-like fruit has a tuft of white bristles and changes from yellow-green to brown, and drops or is blown from the plant. Do not include empty flower heads that have already dropped all of their fruits.

How many fruits are present?

Less than 3;3 to 10;11 to 100;101 to 1,000;More than 1,000

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Ripe fruits
One or more ripe fruits are visible on the plant. For Cirsium occidentale, a fruit is considered ripe when it has turned brown, or when it readily drops or is blown from the spent flower head when touched. Do not include empty flower heads that have already dropped all of their fruits.

What percentage of all fruits (unripe plus ripe) on the plant are ripe?

Less than 5%;5-24%;25-49%;50-74%;75-94%;95% or more

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Recent fruit or seed drop
One or more mature fruits or seeds have dropped or been removed from the plant since your last visit. Do not include obviously immature fruits that have dropped before ripening, such as in a heavy rain or wind, or empty fruits that had long ago dropped all of their seeds but remained on the plant.

How many mature fruits have dropped seeds or have completely dropped or been removed from the plant since your last visit?

Less than 3;3 to 10;11 to 100;101 to 1,000;More than 1,000

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