Scotch Thistle
(Onopordum acanthium L.)
Asteraceae (Sunflower Family)
▲▼ scotch thistle seedlings
▲▼ scotch thistle seedlings, young plants
▲▼ scotch thistle seedlings, young plants
▲▼ scotch thistle seedlings, young plants
▲▼ scotch thistle seedlings, young plants
▲▼ scotch thistle seedlings, young plants
▲▼ first year plants with woolly leaves
▲ center of first year plant rosette showing dense white hairs
▲▼ second-year plant beginning to elongate flowering stem; lower leaves on above plant are nearly 2 feet long
▲ second-year plant beginning to elongate flowering stem
▲▼ wide, continuous, spine-edged wings on stem help distinguish Scotch Thistle from other large thistles
▲▼ wide, continuous, spine-edged wings on stem
▲ wide, continuous, spine-edged wings on stem help even up to base of inflorescences
▲ hollow stems
▲ ▼ mature, flowering plants (late July) in Colorado, about 6 feet tall and almost as wide
▲ mature, flowering plant in western Nebraska
▲ mature, flowering plant in Warnemunde, Germany
▲▼ mature, flowering plant
▲▼ mature, flowering plant
▲ mature, flowering plant, again showing spiny, winged stems
▲ inflorescence in bud
▲▼ inflorescences, showing round-spine-tipped bracts below inflorescence
▲▼ inflorescences
▲ flattened receptacle during flowering senesecence
▲▼ inflorescence receptacle, showing pits that hold seeds/achenes
▲seeds
Scotch Thistle
* noxious weed in Missouri, but not very common; mostly in eastern Missouri
* biennial
* strongly winged stems with long spines on "wings"
* strongly branched, 2-8' tall, usually larger and coarser appearing than other thistles
* basal rosette leaves have fleshy, greyish with whitish-cottony appearance from hairs
* mature leaves, stems covered with dense white hairs, giving plant a grayish appearance
* receptacle at base of head inflorescence is fleshy and pitted once seeds are removed
* can distinguish from tall thistle, bull thistle, musk thistle and field thistle by the pitted receptacle, usually white-woolly leaf and stem appearance and winged stems on scotch thistle
* can distinguish from canada thistle by the presence of creeping roots and much small flower head on canada thistle
* Initiating a biological control evaluation program in California