This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol1", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Lateral sepals wingless, the keel fringed with short hairs.
Lateral sepals winged, the keel erose, fimbriate or lacerate.
Plants not bulbous-thickened at the base; leaves flat or but slightly twisted.
Lateral sepals about as long as the bracts, included, their keels erose to lacerate.
Heads ovoid; bracts relatively few and in few series.
Leaves linear or tapering from the base to the apex.
Lateral sepals nearly entire; heads narrowly ovoid, acute during anthesis.
Lateral sepals toothed; heads broadly ovoid, obtuse.
Leaves broadest at the middle.
Heads oblong or nearly cylindric; bracts numerous, in many series.
Lateral sepals longer than the bracts, exserted, their keels fimbriate or erose-lacerate.
Keels of the lateral sepals erose-lacerate; heads not plumose.
Keels of the lateral sepals long-fimbriate; heads somewhat plumose.
Plants conspicuously bulbous-thickened at the base; leaves spirally twisted.
Xyris flexuosa Muhl. Cat. 5. 1813.
Xyris tort a J. E. Smith, in Rees' Cyclop. 1818.
Scapes slender, straight or sometimes slightly twisted, 4'-18' tall, 2-edged above, bulbous-thickened at the base. Leaves narrowly linear, flat or becoming twisted when old, 1'-6' long, 1/2"-1 1/2" wide; head globose, or short-oblong, obtuse, 3"-4" high; bracts broadly oval or slightly obovate, entire or somewhat lacerate at the apex; lateral sepals linear, about as long as the bracts, curved, finely fringed with short hairs on the wingless keel; expanded flowers 3"-4" broad.