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DescriptionAnnual herbs (in ours). Leaves opposite, undulate or dentate. Capitula small, enlarging in fruit, solitary, radiate, heterogamous. Ray florets female, fertile with a very short yellowish ray; disk florets bisexual, sterile. Phyllaries in 2 series: outer herbaceous; inner covered in hooked spines, enveloping closely the achenes of the female flowers. Receptacle convex, with scales. Achenes of ray florets oblong, smooth, each tightly enfolded in one of the enlarged spiny phyllaries; achenes of disk florets abortive. Pappus 0.