The delicate humped bladderwort (Utricularia gibba) is currently blooming in the pool beneath the entrance bridge to the tropical greenhouse, among the water lily (Nymphaea) plants. It features a small, delicate, insect-pollinated yellow flower protruding a few centimetres above the water surface. However, its more interesting parts are hidden beneath the water surface. The delicate bladderwort is a submerged plant that floats on the water and is not anchored to the substrate, inhabiting standing water pools or those with a slow flow, with low nutrient availability (mainly nitrogen). Its green leaves are divided into slender leaflets that perform photosynthesis. Some of its leaflets develop to create bladder-like organs that trap minute invertebrates swimming in the water. The trap creates a suction effect generated by negative pressure. Special hairs inside the bladder constantly pump out water, creating a negative pressure inside the bladder. A one-directional door, which opens to the inside, covers this chamber and around it are touch-sensitive hairs. When a tiny prey such as a water flea (Daphnia) touches the trigger hairs, the door opens inward and powerfully suctions in the prey together with the water, and then immediately closes. It is the fastest movement in the plant world.
There are over 200 species of bladderwort in the world and two of them in Israel. The aquatic bladderwort (Utricularia australis) became extinct here in the 1940s, while Utricularia gibba is found episodically, occasionally appearing in various water pools, but doesn’t maintain a viable long-term population. The plants in our garden were collected in the 1990s from the Gonen Meadow Nature Reserve in the Hula Valley. These two species have a vast world distribution. However, overexploitation of water sources and wetland degradation threaten them with extinction in Israel as well as the neighbouring Mediterranean countries.
In our Botanical Garden we have two additional species: Utricularia sandersonii, a South-African species, and Utricularia livida, which grows in Central and West Africa, and is currently blooming with white flowers. Neither are free- floating but grow on muddy substrate, and they can be found in the Dafna Carasso tropical greenhouse.

Bladder-like organs

Bladder-like organs, Utricularia gibba