Description Of Plant

Aldrovanda is a monotypic genus in the Droseraceae. The plant consists of a rootless stem whose length can exceed 8 in. (20 cm), and which tends to branch profusely, terminating in a spherical shoot tip with an abundance of protruding bristles. (Photo 6-8) Along the main stem and branches are numerous whorls of leaves arranged like the spokes on a wheel. Each whorl usually consists of 8 leaves about 0.5 in. (1.3 cm) long. Each leaf terminates in a trap which is usually flanked by 6 long bristles that extend beyond the trap. The plant grows by elongation of the stem and branches. (Fig. 6-11)

Flowers

In the spring small, white flowers are borne out of the water on short peduncles which arise from the leaf axils. The flowers consist of 5 petals which are longer than the 5 sepals, 5 stamens and 1 pistil with 5 styles radiating from the top of the ovary each of which terminates in a branching stigma. Up to 20, oval-shaped seeds are produced by the ovary.

TRAPPING

The traps are semi-circular in shape with about 40 trigger hairs on the inner surfaces, 20 on each lobe of the trap. Mucilage, digestive and absorptive glands are all located on the inner lobes. The 2 lobes are joined along the midrib in much the same manner as Dionaea (Venus Fly Trap) lobes. Trap closure is effected by stimulating the trigger hairs. Depending upon the age of the trap and cultural conditions, 1 or more stimulations are required. High temperatures, chemicals and electricity will initiate trap closure. Surrounding the outer edge of the leaves is a row of very closely arranged epidermal hairs sometimes called spikes. These are organized differently than the marginal spikes of the Dionaea. In the latter the hairs lie in the same plane as the lobes and point away from the midrib area. In Aldrovanda the hairs point down into the trap. When the trap closes, the spikes intermesh as they do in Dionaea. This mechanism is

PETAL TRAP

STIGMA

STAMENS

BRISTLE

Aldrovanda Plant

Fig. 6-11 Aldrovanda plant consisting of a rootless stem with whorls of leaves arranged like spokes on a wheel and flowers.

PETAL TRAP

STIGMA

STAMENS

BRISTLE

Fig. 6-11 Aldrovanda plant consisting of a rootless stem with whorls of leaves arranged like spokes on a wheel and flowers.

external with Dionaea, but is internal in the Aldrovanda trap. The intermeshed spikes serve as a sieve or strainer to keep the prey in the trap as it closes and water is forced out. An individual trap can close within 1/50 of a second and with such force as to visibly jerk the whole plant. As in Dionaea, the trap of Aldrovanda becomes narrower with adequate prey. (Fig. 6-12) It takes live, struggling prey to induce the trap to enter the narrowing phase. If digestible prey has been captured the trap will remain closed for about 1 week, if not, it will reopen in a few hours. Each trap can capture several meals before it is exhausted, but if too large a meal is captured, the trap will die. Since growth processes are involved in the working of the traps, increasing age leads to a decrease in functional ability.

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