Aldrovanda vesiculosa

While the genus Aldrovanda is now monotypic, up to 19 extinct species are known in the fossil record. While the species displays a degree of morphological plasticity between populations, A. vesiculosa possesses a very low genetic diversity across its entire range.

A. vesiculosa has declined over the last century to only 50 confirmed extant populations worldwide. These are spread across Europe, Africa, Asia, and Australia. However, potentially invasive populations exist in the eastern United States. It is kept by hobbyists.

Morphology

Aldrovanda vesiculosa is a rootless aquatic plant. Seedlings develop a short protoroot; however, this fails to develop further and senesces. The plant consists of floating stems reaching a length of 6–40 cm (2–16 in). The 2–3 mm (1⁄16–1⁄8 in) trap leaves grow in whorls of between 5 and 9 in close succession along the plant's central stem. The actual traps are held by petioles which have air sacs that aid in flotation. One end of the stem continually grows while the other end dies off. Growth is quite rapid (4–9 mm (3⁄16–3⁄8 in) per day in Japanese populations), so that in optimal conditions a new whorl is produced once or more each day.

Trap

The actual traps consist of two lobes which fold together to form a snap-trap similar to that of the Venus flytrap, except that it is smaller and located underwater. These traps, which are twisted so that the trap openings point outward, are lined on the inside by a fine coating of trigger hairs, snapping shut in response to contact with aquatic invertebrates and trapping them. The closing of this trap takes 10–20 milliseconds, making it one of the fastest examples of plant movement in the kingdom. This trapping is only possible in warm conditions of at least 20 °C (68 °F). Each trap is surrounded by between four and six 6–8 millimetres (1⁄4–3⁄8 in) long bristles that prevent triggering of traps by debris in the water.

Nutrient acquisition

A. vesiculosa is able to grow in nutrient-poor habitats not only due to its carnivory, but also due to its ability to re-utilize nutrients from senesced shoots, and its high affinity for mineral nutrients in water.

Reproduction

Flowers

The small, solitary white flowers of A. vesiculosa are supported above the water by short peduncles which arise from whorl axes. The flower only opens for a few hours, after which the structure is brought back beneath the water for seed production. The seeds are cryptocotylar: the cotyledons remain hidden within the seed coat and serve as an energy store for the seedling. Flowering, however, is rare in temperate regions and poorly successful in terms of fruit and seed development.

Divisions

Aldrovanda vesiculosa reproduces most often through vegetative reproduction. In favourable conditions, adult plants will produce an offshoot every 3–4 cm (1+1⁄8–1+5⁄8 in), resulting in new plants as the tips continue to grow and the old ends die off and separate. Due to the rapid growth rate of this species, countless new plants can be produced in a short period of time in this fashion.

Turions

Winter-hardy Aldrovanda form turions as a frost survival strategy. At the onset of winter, the growth tip starts producing highly reduced non-carnivorous leaves on a severely shortened stem. This results in a tight bud of protective leaves which, being heavier and having released flotational gases, breaks off the mother plant and sinks to the water bottom, where temperatures are stable and warmer. Here it can withstand temperatures as low as −15 °C (5 °F). In the wild, Aldrovanda turions have been observed to have a relatively low rate of successful sinking. Those nutritious turions that fail to sink are then grazed by waterfowl or are killed by the onset of frost. In spring when water temperatures rise above 12–15 °C (54–59 °F), turions reduce their density and float to the top of the water, where they germinate and resume growth. Non-dormant turion-like organs can also form in response to summer drought.