Carelessweed, giant sumpweed
All the western states; most common in the Rocky Mountains and adjacent areas
Usually up to 4 feet; sometimes to 6 feet
Streamsides, fields, disturbed areas, from near sea level to 8,000 feet
Opposite, stalked, toothed, ovate to triangular, up to 7 inches long and 6 inches across
Cyclachaena xanthiifolia, formerly iva xanthiifolia, is the only species in a monotypic genus. Stems are generally unbranched, and bear large leaves at opposite intervals. Leaf shape varies from nearly triangular, the width equal to the length, to ovate, the width less than half the length. Sometimes the leaves are lobed. Leaves have a quite prominent midvein and one or two pairs of major side veins. Leaf edges are lined with large, irregular teeth. There are no basal leaves. Leaf surfaces are rough or very finely hairy, and are dotted with tiny glands.
The small flowerheads form in branched, bractless clusters from the leaf nodes; they have 10, 11 or 12 phyllaries, of two types, all green or purple in color, and (usually) 10 to 15 white, five-lobed florets of which 5 are pistillate and the remainder staminate.