Stems 30-60cm tall, sometimes less, unbranched, fairly rigid, flattened and winged. Leaves equal to shorter, to 4mm wide, palish to somewhat glaucous-green. Spathes two, the outer much longer, sometimes fused at the base. Flowers up to 2.6cm in diameter, rich blue-purple, with the stamen filaments almost totally fused into a tube, summer. North America east of the Rocky Mountains, mainly in grassland. Widely naturalised in Europe including Great Britain. S.m. var. crebrum (syn. S. angustifolium) has rich green foliage, often purple-tinted, and deep violet flowers 2-2.4cm across. Eastern North America from Canada to Virginia, plus Greenland, and naturalised in Europe.