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Yellow Thistle

Cirsium horridulum Michx.

Asteraceae (Sunflower Family)

▲▼ first year rosettes

▲▼ plants initiating flowering

▲▼ plants initiating flowering

▲▼ plants initiating flowering

▲▼ plants initiating flowering,  showing typical "leaning" form of plants

▲▼ plant stems

▲▼ plant stems, showing dense leaves and many fine spines and hairs

▲▼ flower buds

▲▼ inflorescences/flowers

Cirsium horridulum  MIchx., Yellow Thistle: (Bayer Code:  CIRHO; US Code:  CIHO2)

·         Biennial or short-lived perennial thistle native to eastern U.S. grows 1 to 5 feet tall, producing usually one, sometimes several, stems from a basal rosette; leaves and stems often quite hairy, but can be hairless

·         Basal leaves linear to oval-lanceolate with deep, pointed tip lobes, with spines on leaf margins

·         Stem leaves shorter than basal leaves and leaves often overlapping, nearly hiding stems

·         Upper stems may branch in flowering

·         Flowering heads enclosed in many linear, lobed, spiny-edged bract-like leaves; heads 2-3 inches across (or wider); ray flowers are pink or yellow

·         Somewhat similar field thistle (Cirsium discolor) has some bract-like leaves below the head inflorescence, but not so dense as to hide the base of the flower as in yellow thistle, and field thistle stems are not as leafy

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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Posted January 24, 2019