Canada Thistle
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Canada Thistle
Asteraceae (Sunflower Family)
Class A Weed
Description: Canada thistle is a creeping perennial
forming dense populations as a result of extensive
horizontal, branching roots. Stems are up to 5 feet
tall, branched at the top, ridged, and hollow.
Leaves are alternate and lack petioles; margins are
either wavy or lobed, both with a spine. Flower
heads are usually 0.5 inch in diameter, are surrounded by spineless bracts, and have purple
to lavender flowers. White flowers are not uncommon. Male and female flowers are borne on seperate plants. By asexual reproduction, an entire
actively spreading population could be made up of
only male or female plants.
Origin: Europe and Asia; intrduced as a crop seed
contaminant as early as the lat 18th century
Key Characteristics:
- Creeping perennial
- Small flower heads (0.5 inch)
- Male and female flower heads on seperate plants
Distribution: Canada thistle has been identified in the higher elevations of the northern countries and some southern countries.
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