Draft:Utricularia violacea

Utricularia genus

The carnivorous genus Utricularia are commonly known as bladderworts. They are characterised by their tiny traps or 'bladders', which are used to catch prey.^[7] These traps are called utricles, and catch minute animals for digestion, such as rotifers, nematodes and insect larvae.^[8] A single Utricularia plant can bear up to hundreds or thousands of traps.^[9] Utricularia also lack true roots, with many species having rhizoids, stolons or specialised branches depending on their habitat.^[6]

Utricularia species typically have a conspicuous flower that can be purple, yellow, white, blue, brown and red - with numerous combinations of these colours also possible.^[10] All species have a spur below the flower lip, called a corolla spur. This is a key diagnostic feature for classifying the genus and identifying species.^[6]

Most species are found in wet or boggy areas.^[10]

Utricularia violacea

Utricularia violacea is a very small herb, containing only an inflorescence and small leaves above ground, and trap and rhizoids underground. Stolons are absent. The leaves are numerous, a linear - cuneate shape, 0.5mm wide and 4-12mm long. The underground traps are moderately numerous from the stem, ovoid and 1.5-2 mm long. A thin, pointed appendage about 1 mm long is above the trap opening, with a fringed inner margin.^[6]

The inflorescence is 2.5-10 cm tall, either solitary or up to 4 flowers arising together, with the peduncle 0.3-0.5 mm thick. The flower is 4-9 mm long, violet, with yellow in the middle of the lower lip and 3 dark violet lines. The lower lip of the flower is elliptical, 3-8 mm wide, with 3 lobes, while the upper lip is smaller, obovate, with the apex split into two lobes.^[6] Flowering occurs from October to December.^[3][4] The corolla spur is cylindrical and is twice as long as the lower lip. Seed capsule is globose, splitting open longitudinally from the bottom. Seeds are ovoid, 0.3 mm in length.^[3][6]

U. violacea is in section Pleichasia of the genus Utricularia, and is frequently confused with other members of this section, such as U. dichotoma and U. inaequalis in Tasmania, Victoria and South Australia^[6]. U. violacea can also be confused with other species in different sections of the genus Utricularia, if they share a similar distribution and morphology. U. violacea can be confused with U. petertaylorii, U. paulineae and U. tenella in Western Australia, and U. lateriflora and U. tenella in Victoria, Tasmania, and South Australia.^[6]

• 
  U. violacea, with corolla spur ~2x as long as lower lip
• 
  U. petertaylorii
• 
  U. dichotoma
• 
  U. inaequalis
• 
  U. paulineae
• 
  U. tenella
• 
  U. lateriflora

The easiest way to discriminate U. violacea from any of these species is by the length of the corolla spur, relative to the length of the lower lip of the corolla. U. violacea has a corolla spur that is twice the length of the lower lip, while the other listed species have corolla spurs that are a bit longer, smaller or the same length as the lower lip.^[6]

Utricularia violacea is an annual herb that grows primarily in wet heath and swamps at low altitudes, on wet peat, sand or clay.^[6]

In Tasmania, the species is only known to occur from 6 populations on Flinders Island, in swampy verges free of rushes and sedges.^[11] In Western Australia, its distribution is much larger; from 40km north of Perth to Cape Le Grand^[6] - growing in swamps and winter-wet depressions.^[2] The populations in South Australia and Victoria are concentrated in a small area near the coast, at the junction of the two states.^[6] These populations are growing in swamps and wet heath.^[3][4]

Carnivory

Most species of Utricularia photosynthesise from the stem and/or leaves^[12] as well as predating on minute animals with their underground traps (called mixotrophy). Because they typically grow in a boggy, nutrient poor environment - carnivory gives them a competitive advantage over other species which only photosynthesise. Carnivory supplies them with essential nutrients such as nitrogen and phosphorous, which are scarce in their environments.^[12] U. violacea employs this same strategy in the nutrient poor peaty, sandy or clayey soils it lives in, allowing it to effectively compete against larger species.

Microbial Relationships

Utricularia contain miniature ecosystems within their traps, with organisms such as cyanobacteria, algae, microfungi and protozoa living commensally there.^[13] These organisms assist in the breakdown of algae, converting it into a source of utilisable nutrients for the plant. It has been proposed that algae may actually provide more nutrients for the plant than carnivory.^[9] It is likely that U. violacea also possesses these mutualistic relationships with microbes within its habitat.

Lifecycle

The ancestral state of Utricularia species was a perennial life cycle. However, almost 50% of extant Utricularia species are annuals - an evolutionary adaptation to survive through the seasonally drier conditions where these species live.^[14] U. violacea is likely to have evolved an annual lifecycle to survive the hot, dry summers that occur where it grows in Australia. This allows U. violacea to complete its lifecycle between spring and early summer.

Conservation listings for U. violacea in each Australian state it occurs are:

• Tasmania - Rare^[11]
• Western Australia - Not Threatened^[2]
• Victoria - Endangered^[3]
• South Australia - Rare^[4]

The Australian Environment Protection and Biodiversity Conservation Act of 1999 (EPBC Act) does not list the species^[15], indicating that U. violacea is not threatened at a national level, even if rare/endangered in some states. This listing is supported by the International Union for Conservation of Nature (IUCN) listing of Least Concern.^[5]

Population Threats

In Tasmania and Victoria, the main threats to populations of U. violacea are weed invasion, fire regime changes, land use changes affecting hydrology, agricultural intensification, and native marsupial and exotic herbivore grazing.^[11][16] There is a lack of information from South Australia and Western Australia, but it is likely populations there face similar threats.

A major threat to U. violacea populations in the near future across the country is climatic drying. This decreases the likelihood of sufficient winter rainfalls, reducing habitat and potentially exhausting seed banks. This can lead to recruitment failure, and local extinctions of populations.^[16]

Utricularia violacea was first described by Robert Brown in 1810, in his book Prodromus Florae Novae Hollandiae et Insulae Van Diemen. The species belongs in genus Utricularia in the Lentibulariaceae family.^[6][17]

Utricularia originates from utriculus or 'little bladder' in Greek, referring to the underground traps the genus has. The species name violacea originates from Latin violaceus, describing the colour of the flower.^[1]

Utricularia perminuta is regarded as a straightforward synonym of U. violacea.^[6] Ferdinand von Mueller first thought U. perminuta was a separate species in his 1868 book Fragmenta phytographiæ Australiæ^[18], however, George Bentham proved it was a synonym in his 1869 book Flora Australiensis.^[19]

U. violacea is placed within Utricularia subgenus Utricularia and section Pleiochasia according to the infrageneric classification of Peter Taylor in The Genus Utricularia: A Taxonomic Monograph (1989).^[6]

Cultivation is unknown in Tasmania and Australia. Other species of the Utricularia genus are grown around the world - commonly from tropical and subtropical locations.^[20]