Aldrovanda /ˌældrəˈvændə/ is a genus of carnivorous plants encompassing one extant species (Aldrovanda vesiculosa, the waterwheel plant) and numerous extinct taxa. The genus is named in honor of the Italian naturalist Ulisse Aldrovandi, the founder of the Botanical Garden of Bologna, Orto Botanico dell'Università di Bologna.[2] Aldrovanda vesiculosa has been reported from scattered locations in Europe, Asia, Africa, and Australia.[1][3][4][5]
The waterwheel is a small, free floating and rootless aquatic plant, with a length of about 1.5 to 20 cm (9⁄16 to 7+7⁄8 in), and whorls of about 1 to 2 cm (3⁄8 to 13⁄16 in) in diameter.[6] At every 3 to 4 cm (1+3⁄16 to 1+9⁄16 in) the plant branches, sometimes forming offshoots. An average of 12 to 19 whorls spans the length of the plant, each with about 5 to 9 leaves, each up to 11 mm (7⁄16 in) long. The growth is faster than terrestrial carnivorous plants, sometimes growing about 4 to 9 mm (3⁄16 to 3⁄8 in) a day.
In temperate regions the plant goes dormant in the winter, forming turions of about 4–6 mm (3⁄16–1⁄4 in) and sinking to the bottom. In tropical regions, the plant grows all year long without forming turions. The plant flourishes and produces seeds only in these warmer regions, with temperatures higher than 25 °C (77 °F), and produces only one flower, white or light pink, that arises above the surface. In temperate regions, the plant reproduces mostly via asexual means, producing inviable seeds or no flower at all.
The leaf structure is very similar to the Dionaea (commonly known as the Venus flytrap), the main difference being air chambers present in the "stem". The traps, at the end of the leaf, contains up to 6 bristles, analogous to Dionaea teeth, that prevent debris from activating the trap. Each trap contains an additional 60–80 smaller "teeth", and circa 30–40 trigger hairs inside. The speed of closing is about 0.01 to 0.02 seconds.
The trap mechanism is akin to that present in Dionaea - Darwin even named it "the miniature aquatic Dionaea". The mechanism by which the trap snaps shut involves a complex interaction between elasticity, turgor and growth. In the open, untripped state, the lobes are convex (bent outwards), but in the closed state, the lobes are concave (forming a cavity). It is the rapid flipping of this bistable state that closes the trap, but the mechanism by which this occurs is still poorly understood. When the trigger hairs are stimulated, an action potential (mostly involving calcium ions—see calcium in biology) is generated, which propagates across the lobes and stimulates cells in the lobes and in the midrib between them.[7]
The extinct species are known only from fossil pollen and seeds,[8] with the exception of A. inopinata, which is also known from fossilised laminae.[9] Aldrovanda was for a long time thought to be related to the Late Cretaceous form taxon Palaeoaldrovanda splendens, but research published in 2010 suggests that remains attributed to Palaeoaldrovanda actually represent fossilised insect eggs.[10][11]