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|1 Rays reduced or absent, < 5 mm long, the inflorescence therefore compact, appearing like a head; inflorescences opposite the leaves, on peduncles 0-1 (-2) cm long; central schizocarps in each umbellet with both mericarps tuberculate; peripheral schizocarps in each umbellet with only the outer mericarp spiny|
|1 Rays and pedicels well-developed, > 5 mm long, the inflorescence therefore open, distinctly and obviously an umbel; inflorescences opposite the leaves and terminal, on peduncles (1-) 3-16 cm long; schizocarps with both mericarps spiny or sometimes with 1 mericarp tuberculate.|
|..2 Involucral bracts 5-6, generally 1 per ray; fruits 2-2.5 mm long (not including the spines); schizocarps with strongly forward-curved spines, the apices acute with a single erect spicule (thus the spine not appearing hooked), elsewhere on the spines spicules smaller and erect or forward-pointing; mericarps with more or less conspicuous green dorsal ribs, the ribs glabrous or with a few scattered hairs not obscuring the ribs|
|..2 Involucral bracts 0-1 (-3); fruits 3-4 mm long (not including the spines); spines straight or nearly so, with a minute hook at the tip; schizocarps more or less straight to slightly forward-curved spines, the apices barbed with one to two backward-pointing spicules, elsewhere on the spines spicules smaller and erect to backward-pointing; mature mericarp with inconspicuous dorsal ribs, which are obscured by lines of white hairs similar to those on pedicels|
....3 Rays (2-) 4-12; schizocarps with longest spines slightly antrorsely curved, 0.5-1.0 mm long
|....3 Rays 2-3 (-4); schizocarps with longest spines straight, 1.0-1.5 mm long|