Utricularia, commonly and collectively called the bladderworts, is a genus of carnivorous plants consisting of approximately 233 species (precise counts differ based on classification opinions; a 2001 publication lists 215 species). They occur in freshwater and wet soil as terrestrial or aquatic species across every continent except Antarctica. Utricularia are cultivated for their flowers, which are often compared with those of snapdragons and orchids, especially amongst carnivorous plant enthusiasts.

All Utricularia are carnivorous and capture small organisms by means of 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 . Aquatic species, such as U. vulgaris (common bladderwort), possess bladders that are usually larger and can feed on more substantial prey such as water fleas (Daphnia), nematodes and even fish fry, mosquito larvae 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, along with the water surrounding it, is sucked into the bladder. Once the bladder is full of water, the door closes again, the whole process taking only ten to fifteen milliseconds.

Bladderworts are unusual and highly specialized plants, and the vegetative organs are not clearly separated into roots, leaves, and stems as in most other angiosperms. Utricularia lack a root system.

Bladder traps are recognized as one of the most sophisticated structures in the plant kingdom.

Etymology

The generic name Utricularia is derived from the Latin utriculus, a word which has many related meanings but which most commonly means wine flask, leather bottle or bagpipe.

Flowers

thumb|right|[[Utricularia amethystina flower]]

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 wide, and have two asymmetric labiate (unequal, lip-like) petals, the lower usually significantly larger than the upper. They can be of any colour, or of many colours, and are similar in structure to the flowers of a related carnivorous genus, Pinguicula.

About 80% of the species are terrestrial, and most inhabit waterlogged or wet soils, where their tiny bladders can be permanently exposed to water in the substrate. Frequently they will be found in marshy areas where the water table is very close to the surface. Most of the terrestrial species are tropical, although they occur worldwide. The plants are usually found in acidic waters, but they are quite capable of growing in alkaline waters and would very likely do so were it not for the higher level of competition from other plants in such areas. and aquatic life forms arose four times in genus Utricularia. The bladders are usually shaped similarly to broad beans (though they come in various shapes) and attach to the submerged stolons by slender stalks.

Bladders are hollow underwater suction cups, also known as utricles, that possess a valve with bristles that open and close.

The bladder walls are very thin and transparent but are sufficiently inflexible to maintain the bladder's shape despite the vacuum created within. The entrance, or 'mouth', of the trap is a circular or oval flap whose upper half is joined to the body of the trap by very flexible, yielding cells which form an effective hinge. The door rests on a platform formed by the thickening of the bladder wall immediately underneath. A soft but substantial membrane called the velum stretches in a curve around the middle of this platform, and helps seal the door. A second band of springy cells crosses the door just above its lower edge and provides the flexibility for the bottom of the door to become a bendable 'lip' which can make a perfect seal with the velum.

The outer cells of the whole trap excrete mucilage and under the door, this is produced in greater quantities and contains sugars. The mucilage certainly contributes towards the seal, and the sugars may help to attract prey.

Terrestrial species, like U. sandersonii have tiny traps (sometimes as small as 0.2 mm; 1/100")  Additionally, Utricularia traps often collect a diversity of microplankton and detritus. When this periphyton is dissolved into basic nutrients within the bladder environment, bacterial enzymes help aid in digestion. Therefore, carbon secretion and periphyton utilization in the utricles enable Utricularia to live with relatively little competition.

Mutualism could have been an important association in aquatic Utricularia trap evolution as these microbes may have allowed these plants to acquire the needed nutrients when they lost their roots, as they may have had issues acquiring phosphorus. Phosphorus was found to be the most important factor in Utricularia nutrition, which helps explain why Utricularia bladders are found with a wide diversity of bacteria to aid in phosphorus digestion. Such decoupling would allow Utricularia to optimize power output (energy × rate) during times of need, albeit with a 20% cost in energy efficiency.

According to the ROS mutation hypothesis, the sequestration of these protons has cellular consequences, which could lead to nucleotide substitutions. Oxidative phosphorylation is an imperfect process, which allows electrons to leak into the lumen, and only partially reduce oxygen. This partially reduced oxygen is a reactive oxygen species (ROS) which can be very harmful, unlike its fully reduced counterpart, the water molecule. When there is greater potential change between the lumen and intermembrane space, the leakiness of the electron transport chain also increases, therefore creating a higher production of ROS in the mitochondria of Utricularia. ROS is harmful to cells, as it produces damage to nucleotides and helical DNA. Therefore, the increased cellular respiration of Utricularia bladders combined with the unique sequestration of protons could lead to its high nucleotide substitution rates, and therefore its wide diversity. The same model can be used to describe shape development of other leaf shapes, including the pitcher-shaped Sarracenia trap, in terms of the spatial regulation of gene expression. following Müller et al. 2006. Since the sections Aranella and Vesiculina are polyphyletic, they show up multiple times in the cladogram (*). Some monotypic sections have not been included in the study, so that their place in this system is unclear. Sections that are not included below are Candollea, Chelidon, Choristothecae, Kamienskia, Martinia, Meionula, Mirabiles, Oliveria, Setiscapella, Sprucea, Steyermarkia, and Stylotheca in subgenus Utricularia; Minutae in subgenus Bivalvaria; and Tridentaria in subgenus Polypompholyx.

References

  • The International Carnivorous Plant Society
  • Utricularia
  • Botanical Society of America, Utricularia - the Bladderworts
  • Article in Wired magazine featuring video of the plant trapping its food
  • Inner World of Utricularia from the John Innes Centre