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 - White or delicate pink, veined with deep pink, about 1/2 in. long. Five sepals; 5 spreading petals rounded at tips; 10 stamens, 5 longer, 5 shorter, all anther-bearing; 1 pistil with 5 stigmatic styles. Scape: Slender, leafless, 1-flowered, 2 to 5 in. high. Leaf: Clover-like, of 3 leaflets, on long petioles from scaly, creeping rootstock.
Preferred Habitat - Cold, damp woods.
Flowering Season - May - July.
Distribution - Nova Scotia and Manitoba, southward to North Carolina. Also a native of Europe.
Clumps of these delicate little pinkish blossoms and abundant leaves, cuddled close to the cold earth of northern forests, usually conceal near the dry leaves or moss from which they spring blind flowers that never open - cleistogamous the botanists call them - flowers that lack petals, as if they were immature buds; that lack odor, nectar, and entrance; yet they are perfectly mature, self-fertilized, and abundantly fruitful. Fifty-five genera of plants contain one or more species on which these peculiar products are found, the pea family having more than any other, although violets offer perhaps the most familiar instance to most of us. Many of these species bury their offspring below ground; but the wood-sorrel bears its blind flowers nodding from the top of a curved scape at the base of the plant, where we can readily find them. By having no petals, and other features assumed by an ordinary flower to attract insects, and chiefly in saving pollen, they produce seed with literally the closest economy. It is estimated that the average blind flower of the wood-sorrel does its work with four hundred pollen grains, while the prodigal peony scatters with the help of wind and insect visitors over three and a half millions!
Yet no plant, however economically inclined, can afford to deteriorate its species through self-fertilization; therefore, to overcome the evils of in-breeding, the wood-sorrel, like other plants that bear cleistogamous flowers, takes special pains to produce showy blossoms to attract insects, on which they absolutely depend to transfer their pollen from flower to flower. These have their organs so arranged as to make self-fertilization impossible.
Every child knows how the wood-sorrel "goes to sleep" by drooping its three leaflets until they touch back to back at evening, regaining the horizontal at sunrise - a performance most scientists now agree protects the peculiarly sensitive leaf from cold by radiation. During the day, as well, seedling, scape, and leaves go through some interesting movements, closely followed by Darwin in his " Power of Movement in Plants," which should be read by all interested.
Oxalis, the Greek for sour, applies to all sorrels because of their acid juice; but acetosella = vinegar salt, the specific name of this plant, indicates that from it druggists obtain salt of lemons. Twenty pounds of leaves yield between two and three ounces of oxalic acid by crystallization. Names locally given the plant in the Old World are wood sour or sower, cuckoo's meat, sour trefoil, and shamrock - for this is St. Patrick's own flower, the true shamrock of the ancient Irish, some claim. Alleluia, another folk-name, refers to the joyousness of the Easter season, when the plant comes into bloom in England.