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 - Purple, with some orange chrome, I in. broad or less, terminal, solitary, nodding; calyx 5-lobed, purplish, spreading; 5 petals, abruptly narrowed into claws, forming a cup-shaped corolla; stamens and pistils of indefinite number; the styles, jointed and bent in middle, persistent, feathery below. Stem: 1 to 2 ft. high, erect, simple or nearly so, hairy, from thickish rootstock. Leaves: Chiefly from root, on footstems; lower leaves irregularly parted; the side segments usually few and small; the 1 to 3 terminal segments sharply, irregularly lobed; the few distant stem leaves 3-foliate or simple, mostly seated on stem. Fruit: A dry, hairy head stalked in calyx.
Preferred Habitat - Swamps and low, wet ground.
Flowering Season - May - July.
Distribution - Newfoundland far westward, south to Colorado, eastward to Missouri and Pennsylvania, also northern parts of Old World.
Mischievous bumblebees, thrusting their long tongues between the sepals and petals of these unopened flowers, steal nectar without conferring any favor in return. Later, when they behave properly and put their heads inside to feast at the disk on which the stamens are inserted, they dutifully carry pollen from old flowers to the early maturing stigmas of younger ones. Self-fertilization must occur, however, if the bees have not removed all the pollen when a blossom closes. When the purple avens opens in Europe, the bees desert even the primrose to feast upon its abundant nectar. Since water is the prime necessity in the manufacture of this sweet, and since insects that feed upon it have so much to do with the multiplication of flowers, it is not surprising that the swamp, which has been called "nature's sanctuary," should have its altars so exquisitely decked. This blossom hangs its head, partly to protect its precious nectar from rain, and partly to make pilfering well-nigh impossible to the unwelcome crawling insect that may have braved the forbidding hairy stems.