Native. Annual. Propagates by seeds.
Time of bloom: Late July to September.
Seed-time: September to November.
Range: Michigan and Manitoba to the Northwest Territory, southward to Nebraska, New Mexico, Colorado, and Utah.
Fig. 314. - Rough Marsh Elder (Iva ciliata). X 1/6.
Before flowering, this coarse weed somewhat resembles the Great Ragweed (Ambrosia trifida), for the young plants have nearly the same habits of growth and leaf outlines; but as soon as they mature the likeness disappears. Stem stout, woody, and shrub-like, much branched, three to eight feet tall. The lower part of the plant is smooth, but the upper leaves and branches are somewhat roughened with minute hairs. Leaves mostly opposite, broadly ovate, coarsely and very irregularly toothed, roughish above, three-nerved, narrowed abruptly to a stiff petiole; the lowermost ones are sometimes heart-shaped, six inches or more long and nearly as wide. Heads small and greenish, in large terminal panicles and lesser axillary clusters, sessile and closely crowded on the branchlets; they are scarcely an eighth of an inch broad, the disk-florets perfect but sterile; surrounding these are usually five fertile pistillate flowers, with very short tubes or none at all. Achenes usually five in each head, about an eighth of an inch long, ovoid, slightly flattened, varying in color from light brown to nearly black, without pappus. They are sometimes found as an impurity in alfalfa seed. (Fig. 315.)
The required tillage of cultivated crops serves to keep the weed in subjection. In grain fields many of the young seedlings may be dragged out with a weeding harrow in the spring, when the grain is but a few inches tall. The slightly roughened surface of its upper foliage makes this weed susceptible to injury from chemical spray, and, if treated in time with Iron sulfate or Copper sulfate, all seed development may be prevented. Waste-land plants should be cut, piled, and burned before any seed has ripened.
Fig. 315. - Highwater Shrub (Iva xanthifolia).