Rootless, herbaceous perennials or annuals having 2 kinds of leaves that arise from the slender rhizome. The linear or oblong foliage leaves which grow upward can exceed 2.5 in. (6 cm) in length. The second type of leaf, the trap leaves, are 1-6 in. (2.5-15 cm) in length. Scapes which can reach lengths of 16 in. (41 cm) bear several flowers which may be shades of blue, purple, violet, white or yellow. The flowers are very similar to those of Utricularia in structure, which have a 2-parted calyx whereas Genlisea has a 5-parted calyx.
The trap consists of a footstalk which attaches the bulb or bladder to the rhizome From the bulb a hollow tube connects the bulb cavity with the cavities of 2 spiral or twisted cylindrical arms, terminating in an opening, the mouth. One of the arms twists clockwise and the other counterclockwise. This whole structure, called the trapping leaf, usually hangs downward in the water. (Fig. 6-10) The spiral arms can be likened to a long, narrow piece of paper folded in half along its longest axis and then twisted. The result is that the lower edge of the paper is shorter than the top edge. The space between the edges of the paper at each twist forms the trap entrances. In the arms the 2 layers of tissue are bound together periodically with special cells resulting in numerous separated entrances. Once the prey enters the trap, pointed hairs direct it toward the tube which leads to the bulb where digestion takes place or is completed and subsequent absorption occurs. Some botanists believe that the glands between the row of pointed hairs in the arms and tube secrete digestive enzymes and/or mucilage. In the
Fig. 6-9 Genlisia plant including inflorescence, rhizome with rosette of foliage leaves and trap leaves.
Fig. 6-10 Trapping leaf of Genlisia. The footstalk is attached to the rhizome and the bladder or bulb. The bulb is attached to the 2 spiral arms by means of a hollow tube lined with hairs. Insects enter the trap through the spaces in the spiral arms.
Aldrovanda vesiculosa was first observed in India in the 16th century. It was listed «is Lenticula palustris Indica in L. Plukenet's, Almagestum Botanicum of 1696. The Italian physician, Dr. C. Amadei, sent some specimens collected from the Dulioli Swamp neai Bologna, Italy, to the botanist G. Monti. Monti subsequently named the plant Aldrovandia in honor of the naturalist, Ulisse Aldrovandi, in 1747. The name was altered, probably as a clerical error, to Aldrovanda which is now accepted as the correc t name for the genus. Auge de Lassus in 1861, discovering that the traps closed, thought they were air storage organs to give the plant buoyancy in water. Darwin's expo riments with Aldrovanda indicated that absorption of prey took place in the traps anil, realizing the similarity of this plant to Dionaea, assumed Aldrovanda secreted enzymes which digested the prey. Fermi and Buscaglione in 1899 confirmed that Aldrovanda did indeed digest its prey with enzymes produced by the plant. Common names for Aldrovanda are the Waterwheel Plant and Waterbug Trap.
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