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Tall Thistle

Cirsium altissimum L.

Asteraceae (Aster Family)

▲ young rosette with un-lobed leaf margins, white undersides

▲ young rosette with lobed leaf margins, white undersides

▲ bolting flowering stem, with unlobed leaves

▲▼  mature plants, ready to flower

 

▲▼  flower buds

 

▲ ▼ mature, flowering plants

▲ ▼ mature, flowering plants 

▲▼ closer view of inflorescences/flowers 

▲ flower

 

Cirsium altissiumum (L.) Hill, Tall Thistle: (Bayer Code:  CIRAL; US Code:  CIAL2)

         Biennial weed fairly common in southwest Missouri

         Upper leaf surfaces green, lower surfaces white woolly

         Seedling rosette leaves may be lanceolate and unlobed, deeply lobed; margins have short spines and both leaf surfaces are hairy

         Flower stalks short and leafy; head inflorescence flowers purplish pink, blooming in mid to late summer, while invasive musk thistle (Carduus nutans) and plumeless thistle (Carduus acanthoides) flower in late spring (May-June)

         Flower head bases are globe-shaped before flowering, then urn-shaped in flower and have triangular bracts with whitish center stripe and a short spine that sticks outward from each bract tip

         Upper stem leaves are slender and may have no lobes with short spines along the margins, or slender, shallow lobes with spines at the tips of lobes; leaf margins may be bent upward somewhat, but they are not exceptionally wavy as in some other species

         Similar species:

     o   Field Thistle (Cirsium discolor) another native thistle also has white leaf undersides and flower heads similar to tall thistle, but field thistle usually has leaves lobed at least half-way to midvein (not unlobed) in both first-year rosettes and along the upright stems, and the heads have several small leaves forming a small rosette immediately below them, rather than one or no leaves just below the heads as in tall thistle

     o   Bull Thistle (Cirsium vulgare) is a non-native, invasive thistle that has green leaf undersides, and leaf bases extend down the stem to produce some spiny wings; also green cylindrical spines extend out from the bracts below the inflorescence, and there are many cobweb-like hairs wrapped around these green spines

This is one of the native thistles that is sometimes mistaken for an invasive thistle species.  Native thistles provide food and nectar for native insects (including bees and butterflies), birds and other animals, and generally should not be killed indiscriminately.  Maintaining proper grazing levels can often reduce their unwanted increase in pastures and rangeland.

 

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Updated 23 January 2019