Utricularia

A trap that works like a vacuum

Each bladder is a hollow, water-filled leaf organ, usually 1 to 6 mm long in aquatic species and only 0.5 to 1.5 mm in most terrestrial ones ^[16]. Glands inside pump water out until the pressure inside is about 16 kPa below the surrounding water, and the walls bow inward. A watertight door held in place by this pressure closes the mouth ^[16]. When a small animal brushes the trigger hairs on the door, the door flips inward, water and prey rush in, and the door snaps shut again ^{[16, 17]}. ICPS notes that even high-speed cameras catch the prey outside in one frame and already inside in the next ^[18].

How fast is “fast” depends on the method. The classic studies of the 1970s and 1980s timed the whole firing at 10 to 15 ms, while high-speed video in 2011 put it at 2 to 5 ms ^[16]. Vincent and colleagues measured the suction itself at under a millisecond and showed that the door buckles, turning its curvature inside out, then springs back ^[17]. Płachno’s group calls bladderworts the fastest predators in the plant kingdom ^[19].

After firing, the trap pumps out about 40% of its water and is ready again in roughly 25 to 30 minutes ^[16]. Traps also fire on their own every 5 to 20 hours, even without prey ^[17]. Inside, the fluid quickly loses its oxygen, which probably kills the prey by suffocation, and the trap releases digestive enzymes continuously ^{[16, 20]}. Traps of aquatic species are full of bacteria, algae and protozoa, and in nutrient-poor water they often catch little animal prey; the plant feeds this community sugars from its own photosynthesis, and the microbes may in turn supply nitrogen and phosphorus ^[16].

No roots, and an argument about leaves

Bladderworts have no roots ^{[2, 18]}. Beyond that, authorities describe the same organs in different words. The ICPS terrestrial guide says the underground traps are made from true leaves and that the green blades above ground are stalked “adventitious” leaves ^[10]. The ICPS trapping page calls the trap-bearing organs stems and says anything that looks like a normal leaf is a modified stem ^[18]. The New South Wales flora takes a middle line: stems modified to look and work like roots, “leaves” and traps ^[3]. For growers, the practical point is the same either way. What you see above the soil of a terrestrial pot is only part of the plant; the stolons and traps run through the soil, and they invade neighboring pots ^[10].

How many species

WCVP accepts 291 ^[1]. Other sources give lower figures: about 240 in the 2024 New South Wales flora, 211 in Zamudio’s 2005 Mexican flora, and 214 described species when Meyers-Rice wrote in 1992 ^{[3, 2, 13]}. Roughly 50 are aquatic ^[16].

Three ways to grow them

Sources for the table: the two ICPS guides, Adamec’s papers and Pulver ^{[10, 4, 16, 7, 21]}.

Terrestrial bladderworts

ICPS calls the terrestrial species very easy, grown mainly for their flowers, and warns that many become weeds in a collection ^[10]. They are not fussy about soil but need pure water, and too much fertilizer can kill them. Pots can stand in a little water like sundews, or sit in containers without drainage. Some are annuals or short-lived perennials, so collect seed; perennials are kept going by replacing half the soil in a crowded pot with fresh mix, which gives you two pots ^[10]. Seed is sown on the surface of a very wet medium ^[10]; see sowing seeds. Under LEDs they need only moderate light, and strong light encourages cyanobacteria and algae on the soil ^[22].

Epiphytic bladderworts

These come from fog forests in the Caribbean, Central and South America and Africa, and ICPS recommends cool, humid basements and greenhouses, or a large terrarium ^[4]. Mixes are coarse, for example equal parts long-fibered Sphagnum, perlite and pumice, and they appreciate very small amounts of fertilizer in the water ^[4]. Sources disagree on Sphagnum: ICPS prefers Chilean or New Zealand long-fibered moss because it breaks down slowly, while Wyman had no success with it, found that dead long-fibered moss compacts over time, and switched to live Sphagnum ^{[4, 11]}. Wyman grows them at 18 to 23°C by day and about 15°C at night in summer, and warns that long spells above 33°C make plants drop their leaves; tuberous species such as U. alpina can regrow from tubers once it cools ^[11]. See terrariums and humidity.

Aquatic bladderworts

Aquatic species float or anchor loosely in shallow, humic water poor in nitrogen and phosphorus. In good conditions they grow 3 to 4 leaf nodes a day at the tip while the old end decays ^[16]. Temperate species survive winter as turions, dense dormant buds that overwinter at the bottom and rise in spring ^[7]. ICPS lists several North American aquatics among plants that lived outdoors all year in a bog garden in British Columbia ^[9]; see bog gardens. U. gibba can be raised from seed in a jar of distilled water over a layer of washed sand and peat ^[21]. Pesticide use needs care: ICPS warns that some insecticides used against mealybugs kill aquatic bladderworts ^[23].

Pests and problems

Mealybugs hide where leaves meet the stem on epiphytic bladderworts ^[23]; see aphids, mealybugs and scale. Weediness is the more common complaint: the self-pollinating form of U. bisquamata is very difficult to remove from a large collection once established ^[10]. Use low-mineral water for every group.

Conservation

No bladderwort is listed under the US Endangered Species Act ^[24]. The conservation status of the two profiled species is covered on their own pages. ICPS condemns collecting plants from the wild as unethical when nursery stock is easy to find ^[25].