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Utricularia aurea Lour. 1790
pronounced: yoo-trik-yoo-LAR-ee-uh AW-ree-uh
(Lentibulariaceae – the bladderwort family)
common name: Golden Bladderwort
Utricularia is from the Latin utricularius, the master of a raft floated on bladders; aurea is from aureus, golden. This is a genus of carnivorous plants occurring in fresh water and wet soil as aquatic or terrestrial species across every continent except Antarctica. The bladders of the members of the genus were originally thought to be flotation devices until the carnivorous nature of the plants was discovered.
Most species of the genus form long, thin, sometimes branching stems or stolons beneath the surface of their substrate, whether that be pond water or dripping moss in the canopy of a tropical rainforest. To those stolons are attached both the bladder traps and the photosynthetic leaf-shoots, and in terrestrial species the shoots are thrust upward through the soil into the air, or along the surface.
Flowers are the only part of the plant clear of the underlying soil or water. They are usually produced at the end of thin, often vertical inflorescences. They can range in size from 2 mm to 10 cm wide, and have 2 asymmetric labiate petals, the lower usually significantly larger than the upper.
Some South American tropical species are epiphytes, and can be found growing in wet moss and spongy bark on rainforest trees, or even in the watery leaf-rosettes of other epiphytes such as Tillandsia. Rosette-forming epiphytes such as Utricularia nelumbifolia actually put out runners, searching for nearby bromeliads to colonize.
All members of the genus are carnivorous, and capture small organisms by means of their bladder-like traps. Terrestrial species tend to have tiny traps that feed on minute prey such as protozoa and rotifers swimming in water-saturated soil. The traps can range in size from 0.2 mm to 1.2 cm. The aquatic species have the larger bladders, and can feed on more substantial prey such as water fleas, nematodes and even fish fry, mosquito lava and young tadpoles. Despite their small size, the traps are extremely sophisticated. In the active traps of the aquatic species, prey brush against trigger hairs connected to the trapdoor. The bladder, when “set”, is under negative pressure in relation to its environment, so that, when the trapdoor is mechanically triggered, the prey, together with the water surrounding it, is swept into the bladder. Once the bladder is full of water, the door closes again, the whole process taking only 10–15 thousandths of a second.
In Utricularia aurea, the traps are on the leaves; obliquely ovoid, 1–4 mm long; dimorphic, the mouth either lateral or basic. The raceme is erect, emergent, 5–25 cm long, 5–10-flowered; the axis is initially short, elongating in fruit; bracts basifixed, 1–2 mm long; bracteoles absent. The calyx lobes are sub-equal, ovate, 2–3 mm long, elongating to 9 mm long in fruit. The corolla is 10 – 15 mm long, pale yellow with reddish brown veins, externally sparsely to densely hairy, or rarely more-or-less glabrous; the spur is cylindrical, about as long as the lower lip.
Many Australian species of Utricularia will grow only during the wet season, reducing themselves to tubers only 1 cm long to wait out the dry season.
Photographed 2011, Horseshoe Bay lagoon
Page last updated 7th March 2017