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 - Pinkish or bluish purple, butterfly-shaped, about 1/2-in. long, borne in dense, terminal, elongated racemes. Stem; Erect, hairy, leafy, 2 to 8 ft. high. Leaves: Compounded of 3 oblong leaflets, the central one largest; upper leaves nearly seated on stem; bracts, conspicuous before flowering, early falling off. Fruit: A flat pod, about 1 in. long, jointed, and covered with minute hooked bristles, the lower edge of pod scalloped; almost seated in calyx. Preferred Habitat - Thickets, woods, river banks, bogs. Flowering Season - July - September. Distribution - New Brunswick to Northwest Territory, south to
North Carolina, westward to Indian Territory and Dakota.
As one travels hundreds or even thousands of miles in a comfortable railway carriage and sees the same flowers growing throughout the length and breadth of the area, one cannot but wonder how ever the plants manage to make the journey. We know some creep along the ground, or under it, a tortoise pace, but a winning one; that some send their offspring flying away from home, like dandelions and thistles; and many others with wings and darts are blown by the wind. Berries have their seeds dropped afar by birds. Aquatic plants and those that grow beside running water travel by river and flood. European species reach our shores among the ballast. Darwin raised over sixty wild plants from seed carried in a pellet of mud taken from the leg of a partridge. So on and so on. The imagination delights to picture these floral vagabonds, each with its own clever method of getting a fresh start in the world. But by none of these methods just mentioned do the tick-trefoils spread abroad. Theirs is indeed a by hook or by crook system. The scalloped, jointed pod, where the seeds lie concealed, has minute crooked bristles, which catch in the clothing of man or beast, so that every herd of sheep, every dog, every man, woman, or child who passes through a patch of trefoils gives them a lift. After a walk through the woods and lanes of late summer and autumn, one's clothes reveal scores of tramps that have stolen a ride in the hope of being picked off and dropped amid better conditions in which to rear a family.
Only the largest bees can easily " explode " the showy tick-trefoil. A humblebee alights upon a flower, thrusts his head under the base of the standard petal, and forces apart the wing petals with his legs, in order to dislodge them from the standard. This motion causes the keel, also connected with the standard, to snap down violently, thus releasing the column within and sending upward an explosion of pollen on the under surface of the bee. Here we see the wing petals acting as triggers to discharge the flower. Depress them and up flies the fertilizing dust - once. The little gun will not "go off" twice. No nectar rewards the visitor, which usually is a pollen-collecting bee. The highly intelligent and important humblebee has the advantage over his smaller kin in being able to discharge the pollen from both large and smaller flowers.
The Naked-flowered Tick-trefoil (M. nudiflora or D. nudi-florum of Gray) lifts narrow, few-flowered panicles of rosepurple blooms during July and August. The flowers are much smaller than those of the showy trefoil; however, when seen in masses, they form conspicuous patches of color in dry woods. Note that there is a flower stalk which is usually leafless and also a leaf-bearing stem rising from the base of the plant, the latter with its leaves all crowded at the top, if you would distinguish this very common species from its multitudinous kin. The tre-foliate leaves are pale beneath. The two or three jointed pod rises far above the calyx on its own stalk, as in the next species.
The Pointed-leaved Tick-trefoil (M. grandiflora, or D. acuminatum of Gray) has for its distinguishing feature a cluster of leaves high up on the same stem from which rises a stalk bearing a quantity of purple flowers that are large by comparison only. The leaves have leaflets from two to six inches long, rounded on the sides, but acutely pointed, and with scattered hairs above and below. This trefoil is found blooming in dry or rocky woods, throughout a wide range, from June to September.
Lying outstretched for two to six feet on the dry ground of open woods and copses east of the Mississippi, the Prostrate Tick-trefoil (M. Michauxii or D. rotundifolium of Gray) can certainly be named by its soft hairiness, the almost perfect roundness of its trefoliate leaves, its rather loose racemes of deep purple flowers that spring both from the leaf axils and from the ends of the sometimes branching stem; and by its three to five jointed pod, which is deeply scalloped on its lower edge and somewhat indented above, as well.