Annuals or rhizomatous to caespitose perennials; stems terete. Leaf blades terete, sometimes dorsally flattened, rarely laterally compressed (then unitubular and perfectly septate), usually unitubular and perfectly septate, rarely bi- to pluritubular and then perfectly or imperfectly septate. Floral bracteoles absent; flowers in heads or clusters forming anthelate inflorescence, sometimes entirely congested, rarely ±solitary. Seeds apiculate, ±regularly reticulate, with or without tail-like appendages.
The largest section in the genus, comprising 84 species. Centres of diversity in E North America, SW Europe and the Far East.