Bladderwort – Utricularia

The Bladderwort, or Utricularia, is a highly evolved acquatic carnivorous plant. Honestly, they’re probably one of the most highly evolved species of plants, period. They photosynthesize and produce flowers – and that’s about where the similarities between Bladderworts and plants, in general, end. They hold no roots, stems or leaves. Oh yah, and did I mention that they use miniature trap doors attached to digestive-enzyme-secreting bladders to snag and digest unsuspecting aquatic and semi-aquatic prey? Yah, they’re funky. But really, it’s in the best possible way.

With more than 228 species of Bladderworts, they’re also the largest genus of carnivorous plants. With so many species, you’d rightly expect them to be the most geographically widespread carnivorous plant, growing on almost every continent save for frozen Arctic regions and oceanic islands (they’re freshwater aquatic plants). Species are highly adaptable, surviving drought by morphing into underground rice-sized tubers, and freezes by morphing into dormant, hairy buds called turrions. You’ll find them nestled within other plants, like bromeliads, frozen Alaskan swamps, seasonally wet Australian deserts, in fast-moving African waters, in mossy South American trees, and acidic ponds of Florida. There’s nary an environment Bladderworts can’t conquer.

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Biology of a Bladderwort

The trap

Bladderwort traps are one of the most highly-evolved and unique mechanisms in the plant kingdom. At their most basic, they are floating bladder-like trap-doors, about the size of a pinhead in most species (can get as large as 1/4 inch). You’ll find hundreds or thousands of them scattered across the underwater length of Utricularia and they hunt aquatic prey, striking with lighting-fast reflexes in ten-thousandths of one second. Here are the fascinating details:

1. Trap physiology

Bladderwort traps are kidney-shaped (maybe they should have considered the name “Kidneyworts”) and generally between the size of a pinhead and 1/4 inch. You’ll find hundreds or thousands of them underwater, scattered along the length of the plant suspended from small stalks.

The bladder is concave and sealed by a trapdoor that is kept watertight by a sealant made out of mucilage. What all of this adds up to: a low-pressure zone inside of each Utricularia trap. Incredibly, the walls of the bladder are only two cells thick, making them transparent and the perfect viewing window for insects unfortunate enough to find themselves on the inside.

Around the outside of the trapdoor are two types of hairs: Long guide hair that coax prey closer to the trapdoor, and short trigger hairs that line the trapdoor entrance. Read on for how the Utricularia uses this genius mechanism to snatch prey mid-swim.

2. Trapping prey

The guide hair coax prey closer to the trapdoor. One touch of the trigger hairs, and the door swings open at ten-thousands of a second, immediately sucking prey and surrounding water into the low-pressure trap. This spells doom for the unwitting mosquito larvae, water flea, or even tadpole or small hatched fish fry.

Ove the next few minutes, the trap pumps out excess water and reseals itself with mucilage. In as little as twenty minutes, the trap is again ready to catch more prey – up to a dozen insects can be caught by one trap before it looses efficacy.

3. Digesting prey

Glands lining the inside of a Utricularia bladder secret digestive enzymes that dissolve soft-bodied prey within hours. The same glands then slurp up the nutrient-rich soup.

The speed at witch a Bladderwort trap resets leads to a… rather gruesome death for prey too large to be fully sucked in all at once. Mosquito larva and tadpoles will get tales caught in the trap while the rest of them struggles to break free outside of the trap. Struggling re-triggers the trap numerous times, sucking the prey further-and-further into the trap until all that’s left is a protruding head – too big to fit through the trapdoor. Unfortunately for the prey, they’re being digested alive throughout this whole ordeal.

Utricularia biology & requirements

While all Bladderworts employ similar trapping mechanisms, there are around 228 different known species with varied growing conditions across the board. There are terrestrial, aquatic, seasonal, and tropical epiphytic Utricularia. We’ll highlight the main differences, below.

Terrestrial Bladderworts

Some of the easiest Utricularia to grow, you will often find terrestrial bladderworts growing in/around/within your other carnivorous plants due to their prolific nature. They are pan climatic, growing in all of the world’s climate zones. Preferential of permanently wet, peaty sands that occasionally flood, they feast upon tiny prey (think worms and fungus gnat larvae) that inhabit these waterlogged soils. Above-soil, you’ll recognize them by the tiny carpet of leaves – actually photosynthetic stolons – that look like miniature grass and their abundant flowers.

Seasonal Bladderworts

Seasonal bladderworts grow in tropical or Mediterranean climates within Australia. As their name suggests, they grow seasonally, during the wet season, and survive dry seasons through tuber or seed production. Still fairly rare in cultivation, they’re starting to gain popularity through seed propagation.

Tropical Epiphytic Bladderworts

Tropical epiphytic bladderworts grow on cliff sides or in trees among mossy bark and leaf debris in the Caribbean, Central America, the South America (tepui tabletop mountains of Venezuela). They will die back to tubers during dry spells. Great performers in cultivation, they’ll thrive in terrariums and greenhouses, and some can be hardened to sunny windowsills. Highland tropical varieties prefer hothouses and warm houses, but regularly encounter lows into the low 40 degrees Fahrenheit.

Aquatic Bladderworts

As their names suggest, aquatic bladderworts are a free-floating species that do well in fresh, but acidic, waters. They can be tricky to grow in cultivation because they grow very large, requiring small kid-pool-sized containers. Aquatic Utricularia don’t commingle well with algae, but are also harmed by algae-suppressive treatments. The only known way to suppress algae without harming utrics, is to introduce Daphnia (which also make great plant food) that eat the algae. Tadpoles will also control algae, but will turn to eating Utricularia when the supply of algae runs out.

Utricularia foliage is thin, almost fur-like, and looks like branching veins off of the main stem. Traps are interspersed among this foliage, and they together produce a boa-like structure that floats through the water.

During times of drought, some species form turions, or small dormant buds, that keep the plants preserved until water tables rise.

Flowers

Given the diminutive size of their traps and stolons, Utricularia flowers are the showiest and most beautiful part of the plant – rivaling the complexity and showmanship of many orchids. The flowers range in size – with a diameter as large as a 2 inches to as small as 1/4 inch. Color is also a fun Bladderwort flower variable spanning the range of red, yellow, violet, purple, pink, and white – and sometimes including more than one!

Flower anatomy

Bladderwort’s and Butterworts are distant cousins, sharing similarities in flower structure, like upper and lower petals and spurs. Utricularia flowers are small and orchid-like in their intricacy. They can be as tiny as a pin head, or as large as a butterfly, averaging somewhere between 1/4 – 2 inches in diameter. Colors are vibrant reds, violets, purples, pinks, whites, and yellows.

Pollination

Bladderwort flowers are anatomically similar to Butterwort flowers and pollination techniques are similar.

Most Utricularia require hand-pollination, especially when grown indoors. The flowers are designed for pollination by long-tongued pollinators like butterflies. The flicking action of long tongues shuffles around the pollen needed to pollinate.

Looking down the “throat” of the flower, you’ll first see a small apron-like pad on the ceiling – the stigma. Behind this, tucked out of view are the male anthers. To collect pollen, gently insert a toothpick or small paintbrush past the stigma, swipe upwards, and withdraw. Examine your toothpick looking for pollen gains. If you managed to snag some, reinsert the toothpick, dabbing it onto the front-facing stigma.

Seed creation

Sew seed onto the preferred growing medium early in the growing season.

History of the Bladderwort

English botanist James Sowerby assumed the bladders on aquatic species to be small flotation devices in 1797. He did note the copious number of bugs within the bladders, but assumed they were simply “lodging” there… yah, let us know next time your bedroom tries to digest you.

There were numerous botanists independently studying Bladderworts in the mid-1800’s. Ferdinand Cohn discovered prey caught within dried specimens. He tested a theory in 1875 by placing water fleas (daphnia) in an acquarium of live plants. As you’d expect, they all quickly became trapped inside the bladders. Darwin himself assumed that insects forced their way into the bladders. American botanist Mary Treat was the first to observe the trap-door mechanism hoovering insects into the bladders saying “I was forced to the conclusion that these little bladders are in truth like so many stomachs, digesting and assimilating animal food.”

In the early twentieth century, botanists locked onto the true carnivorous nature of Bladderworts. It was Fancis Lloyd in his 1942 Carnivorous Plants, who first described the luring, trapping, and digesting nature of these silent killers.

In 1989 Peter Taylor of England’s Kew Gardens reduced the number of recognized species from 250 to 214. We’ve settled at around 228 recognized species since then.

Where to find Bladderworts in the wild

As mentioned earlier, Utricularia are the most geographically widespread carnivorous plant, growing on almost every continent save for frozen Arctic regions and oceanic islands. You’ll find them in frozen Alaskan swamps, seasonally wet Australian deserts, in fast-moving African waters, in mossy South American trees, acidic ponds of Florida, and beyond.

Cultivation, growing techniques & propagation

Soil

Epiphytic Utricularia: One part long-fibered sphagnum, one part perlite, one part peat, and one part fine orchid bark.

Terrestrial Utricularia: Three parts peat to one part sand or perlite.

Aquatic Utricularia: Mix one cup of peat in each gallon of water to increase acidity.

Containers

3-to-4 inch drained plastic pots are ideal for epiphytic and terrestrial Bladderworts. Most terrestrials will also do well in undrained pots. Try growing terrestrials in clear plastic or glass containers that can be covered below the soil level. When you remove the covering, you will be able to view the sub-soil bladder traps.

Small aquatic species will do well in 1 gallon containers. Large aquatic Bladderworts will require containers that hold, at minimum, 50 gallons of water. This is best accomplished with a fish tank or even a children’s pool.

Large tropical species require 8-to-10 inch pots.

Watering

Use distilled or reverse osmosis water. This can be inexpensively purchased in most grocery stores, or you can invest in a reverse osmosis (RO) filtration system that hooks up to a sink (bonus – this also provides great drinking water for humans and pets).

Keep terrestrials in a water tray and fill this tray to maintain wet soil. Many enjoy occasional flooding, and deep water trays that rise above the surface level of the soil will help. Alternatively, use undrained pots to accomplish flooding.

Epiphytic species do best in shallow water trays with overhead watering. Keep soil wet during the growing season, and barely damp during the winter months for those plants that require a dormancy.

Aquatic species obviously don’t require traditional “watering,” but may require a change of peaty water if algae gets dense. Gently rinse the plants to remove algae before introducing them into new water.

Lighting

Full-to-part sun for most species. Note: sun will induce flowering.

Feeding

Introduce water fleas (daphnia) into the environment of aquatic bladderworts. Simply collect some local pond water teaming with life and introduce it into your utric’s water.

All other varieties will naturally feed on microscopic life and fungus gnat larvae that grow in the soil. If you’re flooding your terrestrial Utricularia, introduce water fleas.

Fertilizers

A light monthly fertilizing at 1/4 strength is appreciated. Foliar feed by misting onto foliage. For aquatics, sprinkle the water with this diluted fertilizer.

Transplanting

Transplanting is easy and best done early in the growing season for healthy new growth. Try propagating new colonies of Utricularia every two or three years.

Divisions

Utricularia divisions are a little different than most carnivorous plant species. Since many Bladderworts are clumping plants, separate colonies of plants into smaller colonies and simply plant these in their own growing medium.

For aquatics, separate 3-4 inch portions to place in new water. For terrestrials and epiphytes, 2 square inch clumps, including surface stolons, will start new colonies nicely.

Cuttings

Propagation via Utricularia leaf cuttings are also possible. Pluck stolons from the parent plant, place on the surface of the preferred soil, and keep humid – the same as you would for a Sundew leaf cutting. Larger leaves can be cut into 2 inch sections and rooted.

Seed

See the section above for Bladderwort flower anatomy and pollination techniques.

Germination is accomplished by sparsely sewing seed onto the specie’s preferred medium and keeping conditions humid and bright for a few weeks. Use a seed tray for non-aquatic varieties.

Tissue Culture

Not popular tissue culture plants due to the ease of traditional means of propagation.

Diseases & Pests

Algae can be a pain for aquatic species. Water fleas will both eat the algae and feed the plants. Even if algae gets bad, avoid using algaecides. Instead, change out the plant’s water. Do note that if algae is too sparse, tadpoles living alongside Utricularia will turn to eating them, instead.

For soil-based species, aphids can be taken care of using an insecticide or flea collar. Scrape algae from the soil’s surface.

Climate

Model growing conditions after the respective species’ natural environment.

Outdoors

Again, model growing conditions after the respective species’ natural environment. Many terrestrial Utricularia will thrive alongside other carnivorous plants in bog gardens. Large aquatic species will do well in pools and man-made ponds within bog gardens.

Greenhouses

Terrestrial and epiphytic species will do well in cool and warm houses. Large aquatics will do better outdoors in pools.

Terrariums

Tropical, subtropical, and warm temperate terrestrial plants will thrive in well-lit terrariums. So will tropical epiphytes.

Windowsills

Small aquatics like Utricularia gibba will do well. Terrestrials will thrive in sunny windowsills. Try U. sandersonii, or U. livida. Utricularia humboldtii, U. reniformis, and U. longifolia are good epiphytic candidates.

Bog gardens

Once more, model growing conditions after the respective species’ natural environment. Many terrestrial Utricularia will thrive alongside other carnivorous plants in bog gardens. Large aquatic species will do well in pools and man-made ponds within bog gardens.