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Key to Acanthospermum

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1 Stems prostrate and rooting at the nodes; bur 7-9 mm long, slightly compressed, strongly 5-7-ribbed
1 Stems erect; bur 2-6 mm long, obviously compressed, obscurely ribbed or 3-ribbed.
  2 Leaves (2-) 4-12 (-15) cm long, sessile or subsessile; bur with prickles on all surfaces
  2 Leaves 1-3 (-4.5) cm long, petiolate, the petiole 4-18 mm long; bur unarmed or nearly so on the side faces, the prickles along the ribs and around the tip