How to identify Yellow star-thistle (Centaurea solstitialis)
Yellow star-thistle, also known as Yellow cockspur, Barnaby's thistle, Geeldissel, Yellow centaury
Yellow star-thistle exhibits a distinctive appearance with bright yellow flower heads surrounded by light green bracts adorned in fine, cobweb-like hairs. These bracts harbor robust, straw-colored spines spanning 1-2 inches (2.5-5 cm) in a star pattern, offering a key identifying trait. The plant is a visually striking member of the Asteraceae family, with thistle-like characteristics that make it recognizable.
Lifespan: Annual, Biennial
Plant Type: Herb
Leaf Type: Semi-evergreen
Bright yellow flower heads surrounded by light green bracts with cobweb-like hairs.
Straw-colored spines measuring 1-2 inches (2.5-5 cm) in a star pattern.
Distinctive stout, needle-like spines radiating in a star-like formation around bright yellow flowers.
Fruit is a quarter-inch (6 mm) achene with tuft of short, stiff, light brown bristles at tip.
Leaves alternate, toothless, and covered in woolly hairs, forming a rosette with wavy edges.
The leaves of yellow star-thistle are alternate and form a basal rosette up to 6 inches (15 cm) long when young. They are often lobed in narrow sections on the lower half and taper to a short stalk, but the rosette withers by the time the plant flowers. All leaves are toothless, covered in woolly hairs, giving them a gray-green cast. As they move up the stem, they become much smaller, linear-oblong, undivided, and have bases extending down the stem, forming wing-like, often wavy edges.
The flowers of yellow star-thistle are distinctive with their bright yellow color. Each flower head is surrounded by bracts armed with stout, needle-like, straw-colored spines, measuring 1 to 2 inches (2.5 to 5 cm) in length that radiate in a star-like formation. The flower heads are typically small and compact, enhancing their visual impact and aiding in easy identification. The flowers bloom during summer, emitting no discernible scent, but their striking shape and formidable bracts make them easily noticeable.
The stem of yellow star-thistle is erect, slender, and prominently hairy, enhancing its distinctive texture. It exhibits a branching pattern with stems growing up to 3 feet (90 cm) tall, contributing to its upright and spindly appearance. The stem's surface is covered with fine hairs, giving it a slightly rough texture, and it features a green color, transitioning to a more robust and thicker structure as it matures. The noticeable hairiness and branching nature are key for its identification.
The fruit of yellow star-thistle is an achene that is finely hairy and measures approximately a quarter-inch (about 6 mm) in length. Upon reaching maturity, this fruit becomes straw-colored, and it is noteworthy for its tuft of short, stiff, light brown bristles situated at the tip. The seeds of yellow star-thistle are commonly found to remain within the seed-heads throughout the late fall or winter, suggesting a delayed dispersion strategy. These characteristics make it a distinct element for identification.
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Scientific Classification of Yellow star-thistle
