This section is from the book "Nature's Garden", by Neltje Blanchan. Also available from Amazon: Nature's Garden; An Aid To Knowledge Of Our Wild Flowers And Their Insect Visitors.
Flowers - Blue, later purple; 1/2 in. long, growing downward in i-sided spike, 15 to 40 flowered; calyx oblique, small, with unequal teeth; corolla butterfly-shaped, consisting of standard, wings, and keel, all oblong; the first clawed, the second oblique, and adhering to the shorter keel; 10 stamens, 1 detached from other 9. Stem: Slender, weak, climbing or trailing, downy, 2 to 4 ft. long. Leaves: Tendril bearing, divided into 18 to 24 thin, narrow, oblong leaflets. Fruit: A smooth pod 1 in. long or less, 5 to 8 seeded.
Preferred Habitat - Dry soil, fields, waste land.
Flowering Season - June - August.
Distribution - United States from New Jersey, Kentucky, and Iowa northward and northwestward. Europe and Asia.
Dry fields blued with the bright blossoms of the tufted vetch, and roadsides and thickets where the angular vine sends forth vivid patches of color, resound with the music of happy bees. Although the parts of the flower fit closely together, they are elastic, and opening with the energetic visitor's weight and movement give ready access to the nectary. On his departure they resume their original position, to protect both nectar and pollen from rain and pilferers whose bodies are not perfectly adapted to further the flower's cross-fertilization. The common humblebee (Bombus terrestris) plays a mean trick, all too frequently, when he bites a hole at the base of the blossom, not only gaining easy access to the sweets for himself, but opening the way for others less intelligent than he, but quite ready to profit by his mischief, and so defeat nature's plan. Dr. Ogle observed that the same bee always acts in the same manner, one sucking the nectar legitimately, another always biting a hole to obtain it surreptitiously, the natural inference, of course, being that some bees, like small boys, are naturally depraved.
In cultivated fields and waste places farther south and westward to the Pacific Coast roams the Common or Pebble Vetch or Tare (V. saliva), another domesticated weed that has come to us from Europe, where it is extensively grown for fodder. Let no reproach fall on these innocent plants that bear an opprobrious name: the tare of Scripture is altogether different, the bearded darnel of Mediterranean regions, whose leaves deceive one by simulating those of wheat, and whose smaller seeds, instead of nourishing man, poison him. Only one or two light blue-purple flowers grow in the axils of the leaves of our common vetch. The leaf, compounded of from eight to fourteen leaflets, indented at the top, has a long terminal tendril, whose little sharp tip assists the awkward vine, like a grappling hook.
The American Vetch, or Tare, or Pea Vine (V. Americana) boasts slightly larger bluish-purple flowers than the blue vetch, but fewer of them; from three to nine only forming its loose raceme. In moist soil throughout a very broad northerly and westerly range it climbs and trails its graceful way, with the help of the tendrils on the tips of leaves compounded of from eight to fourteen oblong, blunt, and veiny leaflets.