Dig deeper at SERNEC, a consortium of southeastern herbaria.
Check out EDDMapS.org to see where this has been reported.
Spermatophytes (seed plants): Angiosperms (flowering plants): Eudicots: Core Eudicots: Asterids: Campanulids: Asterales
PLANTS National Database
Xanthium strumarium var. canadense
Vascular Flora of the Carolinas (1968)
Xanthium strumarium var. strumarium
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JK Marlow jkm150226_737b
February Pickens County SC
Phyllaries mostly hooked, the whole becoming a hard prickly perigynium (bur), per Flora of North America.
JK Marlow jkm130928_750b
September Spartanburg County SC
Leaf blade broadly ovate to roughly orbicular, base cordate or nearly so, per Wildflowers of the Eastern United States.
Gill Newberry gn10_x_cocklebur
Female flowers enclosed by the involucre, forming a bur w hooked bristles, per Wildflowers of the Eastern United States.