=Wild Teasel.= _Dipsacus sylvestris_ Huds. Achene brown, minutely hairy, 4 mm. long, oblong, square in cross-section, with four vertical ribs on the angles and four on the sides. Seed suspended, anatropous, supplied with endosperm. Introduced from Europe. A weed requiring two years from seed to seeding.
=Yarrow. Milfoil.= _Achillea Millefolium_ L. Flowers white; achenes white to gray, finely striate lengthwise, flattened, oblong, tapering at the lower end, straight or curved. 2-2.3 long. Most likely introduced from Europe.
=Ragweed.= _Ambrosia artemisiifolia_ L. Achenes hard, straw-colored to light brown or black, top-shaped, broadly oval, 2.5-3 mm. long, besides the beak 1.5 mm. long, the sides irregularly ridged vertically, with 5-10 short teeth at the apex. Sometimes the hard covering is removed by a clover huller, exposing the naked seed. Native of the U. S.
=Great Ragweed.= _Ambrosia trifida_ L. Achenes hard, brown, more or less mottled, top-shaped, 7-8 mm. besides the stout beak 2-3 mm. long, sides with 5 stout ridges terminating in 5 short teeth. Native to the United States. River bottoms, low land, sometimes 15 ft. high.
=Corn Camomile=. _Anthemis arvensis_ L. Achenes very variable, creamy white to light brown, oblong, wedge-shaped in outline, circular to four-angled in cross-section, more or less ribbed lengthwise, a ripple-shaped scar at the narrow end; apex truncate with a minute projection in the center, often with a narrow ridge about the margin. About 1.7 mm. long. Introduced from Europe. Seldom troublesome in Michigan.
=May-weed. Dog's-Fennel.= _Anthemis Cotula_ L. Outer flowers white; achenes straw color to light brown, obovoid (large end uppermost) to oblong, circular in outline, 1.3-1.8 mm. long, with 10 warty ribs. Introduced from Europe. Old roads and waste places.
=Great Burdock.= _Arctium Lappa._ So far as I have seen the achenes of this species, when compared with A. minus, are darker colored, rather longer, the ribs more distinct.
=Smaller Burdock.= _Arctium minus_ Beruh. Possibly only a variety of _A. Lappa_ L., but the prevailing plant in central Michigan. I see no way of distinguishing the achenes of one from the other; but it makes little difference as one burdock is as bad as another.