Everything about Utricularia totally explained
Bladderwort is the common name given to the plants of the genus
Utricularia. The largest genus of
carnivorous plants, it consists of some 215 species which occur in fresh water and wet soil across every continent except Antarctica. Bladderworts are cultivated for their
flowers which are often compared with those of
snapdragons and
orchids.
All bladderworts are carnivorous, and capture small organisms by means of bladder-like traps. Terrestrial species tend to have tiny traps, and feed on minute prey such as
protozoa and
rotifers swimming in water-saturated soil. However, in aquatic species such as the Common Bladderwort
U. vulgaris, the bladders are large (sometimes exceeding 5 mm in diameter) 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. When prey animals brush against trigger hairs connected to the trapdoor, it's released and the bladder sucks in the door and the prey, along with the water surrounding it. Once the bladder is full of water, the door closes again, the whole process taking only ten to fifteen thousandths of a second.
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. The bladder traps, conversely, are recognized as one of the most sophisticated structures in the
plant kingdom.
Physical description
The main part of a bladderwort plant always lies below the surface of its substrate. Terrestrial species sometimes produce a few photosynthetic leaf-shoots which lie unobtrusively flat against the surface of their soil, but in all species only the flowering stems rise above and are prominent. This means that the terrestrial species are generally visible only while they're in flower, although aquatic species can be observed below the surfaces of ponds and streams.
Plant structure
Most species 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 these stolons are attached both the bladder traps and photosynthetic leaf-shoots, and in terrestrial species the shoots are thrust upward through the soil into the air or along the surface.
The name
bladderwort refers to the bladder-like traps. The generic name
Utricularia is similarly derived from the Latin
utriculus, a word which has many related meanings but which most commonly means
wine flask or
leather bottle. The aquatic members of the genus have the largest and most obvious bladders, and these were initially thought to be flotation devices before their carnivorous nature was discovered.
Flowers and reproduction
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 stems. They can range in size from a few millimetres across to two inches or more, 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.
The flowers of aquatic varieties like
U. vulgaris are often described as similar to small yellow
snapdragons, and the Australian species
U. dichotoma can produce the effect of a field full of
violets on nodding stems. The epiphytic species of South America, however, are generally considered to have the showiest, as well as the largest, flowers. It is these species that are frequently compared with
orchids.
Certain plants in particular seasons might produce closed, self-pollinating (
cleistogamous) flowers; but the same plant or species might produce open, insect-pollinated flowers elsewhere or at a different time of year, and with no obvious pattern. Sometimes, individual plants have both types of flower at the same time: aquatic species such as
U. dimorphantha and
U. geminiscapa, for example, usually have open flowers riding clear of the water and one or more closed, self-pollinating flowers beneath the water
(1). Seeds are numerous and small, sometimes as small as 0.2 mm.
Distribution and habitat
Utricularia can survive almost anywhere where there's fresh water for at least part of the year: only Antarctica and the oceanic islands have no native species. The greatest species diversity for the genus is seen in South America, with Australia coming a close second.. 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.
┌──── Section Avesicaria ┐
┌─────┤ │
│ └──── Section Vesiculina
* │
┌─────┤ │
│ │ ┌────
Utricularia olivacea │
│ └─────┤ │
┌─────┤ └──── Section Vesiculina
* │
│ │ │
│ └──────────────── Section Nelipus │Subgenus
┌─────┤ │Utricularia
│ │ ┌──── Section Lecticula │
│ └─────────────────┤ │
┌─────────────────────┤ └──── Section Utricularia │
│ │ │
│ │ ┌──── Section Orchidioides │
│ └───────────────────────┤ │
│ └──── Section Foliosa ┘
│
│ ┌──── Section Oligocista ┐
│ ┌─────┤ │
│ │ └──── Section Avesicarioides │
│ ┌─────┤ │
│ │ └────────── Section Benjaminiana │
┌─────┤ ┌─────┤ │
│ │ │ │ ┌──── Section Stomoisia │
│ │ │ └───────────┤ │
│ │ ┌─────┤ └──── Section Enskide │
│ │ │ │ │
│ │ │ └────────────────────── Section Aranella
* │Subgenus
│ │ ┌─────┤ │Bivalvaria
│ │ │ │ ┌──── Section Calpidisca │
│ │ │ └───────────────────────┼──── Section Lloydia │
│ │ ┌─────┤ └──── Section Australes │
│ │ │ │ │
│ │ │ │ ┌──── Section Nigrescentes │
│ └─────────┤ └─────────────────────────────┤ │
│ │ └──── Section Phyllaria │
│ │ │
│ └──────────────────────────────────────── Section Aranella
* ┘
│
│ ┌──── Section Pleiochasia ┐Subgenus
└───────────────────────────────────────────────────┤ │Polypompholyx
└──── Section Polypompholyx ┘
Footnotes
- Taylor p. 39
- c.f. Slack p. 165
- c.f. Slack p. 168: Slack successfully introduced U. vulgaris to alkaline pondwater.
- D'Amato p. 220
- Lloyd p.213
- Slack p.165; Cheers, chapter Utricularia; LLoyd has an extensive discussion of the evidence in chapter XIV The Utricularia Trap and provides schematic diagrams representing the traps' complexity in analogy to an imaginary mousetrap involving 26 separate mechanisms. Also c.f. Taylor (Introduction) and D'Amato pp. 221-222.
- Lloyd, ibid.
- ibid. p. 241
- ibid.
- ibid. p. 251
- ibid. pp. 252-253; c.f. also Slack pp. 222-223 who gives the earlier hypothesis
Further Information
Get more info on 'Utricularia'.
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