Harmony and Conflict in the Living World - Alexander F. Skutch [58]
Thirty species of butterworts are distributed throughout the North Temperate Zone, reach the Arctic, and grow on high tropical mountains. In acid bogs, mossy banks, or damp crevices in stony outcrops, the perennial rootstocks bear compact rosettes of soft,
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fleshy leaves that usually press the ground or rock face. Their spurred flowers, borne singly on slender scapes, are white, yellow, blue, pink, or purple, often so large and handsome that they are cultivated as ornamentals. Some resemble violets. These plants of the bladderwort family receive their generic name, Pinguicula (from pinguis, fat), because the leaves of some are greasy to the touch. They are called butterworts apparently because the Lapps of northern Scandinavia pour the still-warm milk of their reindeer cows through sieves lined with these leaves, which contain a rennetlike substance that coagulates the milk into a sort of butter.
Pinguicula vulgaris, widespread in both Eurasia and North America, is the species in which Darwin first demonstrated the carnivorous habit of butterworts. Its ovate, entire leaves are thickly studded on the upper side with slalked glands that glisten with mucilage attractive to small flies. Between them lie more numerous sessile glands, the function of which is digestive. The margins of the leaf are incurved. When a little insect sticks to the mucilage glands toward the sides of a leaf, the edges slowly curl farther inward, bearing the captive toward the center and forming a broad and shallow trough that helps retain the liquids profusely secreted by the glands. These contain an enzyme that digests the victim, or almost any kind of protein placed upon the leaf, along with a weak acid disinfectant. The inrolling, which appears to leave the leaf's broad central zone uncovered, may continue for several days, after which, with the completion of digestion and absorption, the movement is reversed and the leaf flattens out again. Butterwort leaves can deal effectively with only very small insects, such as tiny flies; larger victims putrefy and damage the tissues. As a carnivorous plant, Pinguicula combines features of Drosophyllum and Byblis, in which glandular leaves attract and passively hold prey, and of Dionaea and Aldrovanda, in which leaves close over the booty much more swiftly and completely.
Suction Traps
The largest genus of carnivorous plants is Utricularia, the bladderworts, with about 275 species of worldwide distribution. In the North
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Common butterwort, Pinguicula vulagris, flowering plant
Temperate Zone these plants float in still water, above which they lift only their flowers, or less often they grow on wet, sandy shores. Most widespread and familiar is the Greater Bladderwort, U. vulgaris, with rootless stems, up to a yard long, supporting leaves dissected into many capillary divisions that bear tiny bladders. Of the more numerous species in the tropics, some are aquatic like the
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northern forms but most grow as epiphytes on mossy trunks and branches, or on the ground, often amid mosses or humus in which their bladders are hidden. U. nelumbifolia flourishes in the aerial pools of rainwater caught in the tight rosettes of epiphytic tank bromeliads, spreading from tank to tank by means of runners. Two species, U. neottioides of Paraguay and southern Brazil and U. rigida of Africa, depart from bladderworts' preference for still waters by growing attached to rocks in swiftly flowing streams, in the manner of river-weeds of the family Podostemonaceae. Some epiphytic bladderworts store water for the dry season in tubers.
Wherever they grow, bladderworts most attract our attention when they send flowering stalks above the water or moss that covers them. In swamps of western Australia, long inflorescences of U. volubilis twine around supporting reeds. Some epiphytic species are so small and inconspicuous