Humped Bladderwort

Utricularia gibba, the humped or floating bladderwort, is a small aquatic carnivorous plant that forms mats of thread-like stems in shallow water and catches tiny animals in suction bladders 1-2.5 mm long. It grows on every continent except Antarctica and has one of the smallest genomes known in a plant.

U. gibba forms loose mats of branching, criss-crossing stolons, each about 20 cm (8 in) or longer and only 0.2-1 mm thick, with small rootlike rhizoids near the flower stalks. Leaf-like organs 0.5-1.5 cm long, forked into a few hair-like segments, grow along the stolons, and some of their tips are replaced by bladder traps. The plant can float freely or anchor itself in the mud of the bottom; it flowers far more when supported by a substrate in shallow water.

Erect flower stalks rise above the water, usually a few centimeters and up to about 20 cm tall, each with typically two to six yellow flowers, often with reddish-brown veins. The upper lip of the flower is nearly round and usually larger than the lower lip, whose inflated central bulge gives the species its name: gibba is Latin for hump or swelling. Flower size varies widely across the range; the main variation within the species is in flower size. Submerged plants can also produce closed, self-pollinating flowers.

It is one of the most variable species in the genus, and more than sixty names once applied to forms of it, including U. exoleta, U. obtusa and U. biflora, are now treated as synonyms.

Itulagi: Nearly worldwide in warm regions; native range includes eastern North America, Central America, the Caribbean, southern Africa and southern India

Sone o le Tau: Tropical to warm temperate; widespread

It grows in still or slowly flowing fresh water: ponds, lakes, ditches, pools, bogs, swamps and marshes, usually only several centimeters deep and typically poor in phosphorus and nitrogen. In deep water it can grow as a free-floating plant but rarely flowers unless the flower stalks are supported near the surface. It prefers warm climates and flowers in the warm season, or all year in the tropics. Outside its native range it has become invasive in places including Hawaii, Australia, Japan, New Zealand and the United Kingdom.

Fuamatua: Stolons about 8 in (20 cm) or longer; flower stalks a few inches, up to 8 in (20 cm)

Fuafuaga o le Tuputupu ae: Fast

Ituaiga Mailei: Bladder Trap

The bladders are among the most complex traps of any carnivorous plant. Each oval bladder, 1-2.5 mm long, pumps water out through special glands so that the pressure inside is lower than outside, while a trap door held shut by a ridge and mucilage keeps it sealed. When a small aquatic animal touches the bristly appendages near the door, the door gives way, water rushes in, and the prey is sucked inside in as little as a thirtieth of a second. The door closes again and the bladder secretes enzymes that digest the prey over a few hours to a few days, then resets.

Its sequenced genome is only about 82 million base pairs, exceptionally small for a plant, yet holds a typical number of genes.
Only about 3% of its DNA is repetitive, which challenged the idea that large amounts of non-coding 'junk' DNA are needed.
Despite the tiny genome, it has gone through at least three rounds of whole-genome duplication since sharing an ancestor with tomato and grape.
A bladder can suck in prey in about 1/30 of a second.
It is often described as a weed in cultivation because it grows so readily.

Linnaeus included U. gibba among the seven bladderworts he listed in Species Plantarum in 1753. For a long time the bladders of Utricularia were thought to be floats; in the 1870s the American naturalist Mary Treat realized they were suction traps, and Charles Darwin and later Francis Lloyd studied them further. Because the species is so variable across its huge range, more than sixty forms were described as separate species over the following two centuries. Peter Taylor, in his 1989 monograph of the genus, merged them all into U. gibba, including the North American 'U. biflora' and the original 'U. fibrosa' of Walter.

In 2013 researchers published the sequence of its 82-megabase genome in Nature, making it a model for the study of genome size. The IUCN Red List assessed the species as Least Concern in 2019.

1. Utricularia gibba, Wikipedia
2. Rice, B. (1994) Focusing on U. gibba: the "U" stands for ubiquitous. Carnivorous Plant Newsletter 23(1): 19
3. Utricularia: the bladderworts, The Carnivorous Plant FAQ (Barry Rice)
4. About affixed aquatic Utricularia, The Carnivorous Plant FAQ (Barry Rice)
5. Ibarra-Laclette, E. et al. (2013) Architecture and evolution of a minute plant genome. Nature 498: 94-98
6. Lansdown, R.V. (2019) Utricularia gibba. The IUCN Red List of Threatened Species