Cultivating Carnivorous Plants (2015)

ALDROVANDA

Aldrovanda vesiculosa in cultivation.

The Waterwheel Plant, Aldrovanda vesiculosa, is sometimes called the Venus Flytrap of the aquatic world

for good reason. The traps of the Waterwheel Plant are nearly identical to the Venus Flytrap’s. Aldrovanda

traps are arranged in a whorl of five to nine per cross-section of plant. Each trap is two-lobed with trigger

hairs inside, much like a Venus Flytrap. Just like a Venus Flytrap, stimulation of trigger hairs by aquatic prey

causes the trap to snap shut via rapid cell growth. As the prey struggles to escape, the trap closes tighter and

NATCH GREYES

releases digestive enzymes. In time,

the prey succumbs to the fluid and

is “eaten” by the plant.

Each whorl of traps is

connected to a central stem, along

which the plant grows. New trap

whorls are produced on the leading

side of the stem while old whorls die

off on the trailing side. In good

conditions, the leading edge will

split, causing the plant to branch. In

time, the trailing side will catch up

to the branching side, and the plant

will then divide into two plants.

In warm summers, the plants

flower. Each plant produces up to

five flowers with white petals. Most

plants only have one flower; two or

more flowers are rare. The flowers

open above the water for only a few

short hours. After closing, the

flowers sink beneath the water to

begin seed production. The seed is

small, black, and rare. Few flowers

are pollinated successfully, and

fewer are successful at producing

seed, particularly in temperate

regions, where the temperature

Aldrovanda vesiculosa traps.1

rarely gets warm enough to induce

flowering.

During the winter, plants in temperate regions form winter buds, called turions, that sink to the bottom

of the pond to await spring. If successful at sinking, the turions can withstand temperatures down to 5° F (-

15° C). Most turions, however, are not correctly formed. Of those that are correctly formed, not all will sink.

This failure to sink results in most turions being eaten by waterfowl or killed by frost.

Similar to the Venus Flytrap, only one species of Aldrovanda, vesiculosa is currently in existence. Fossil

records reveal, however, that up to 19 different species were once in existence, although it is not currently

known if any of those evolved into Aldrovanda vesiculosa. Still, despite having only one species, Aldrovanda has

managed to spread nearly worldwide, with populations stretching from Europe to Australia.

Although having a distribution from Europe to Australia, Aldrovanda has the reputation of being one of

the most challenging aquatic carnivorous plants to cultivate long-term. In the wild, it is rare, often growing in

still bodies of freshwater in the company of aquatic species of Utricularia, water lilies, and reed-like plants.

Despite this reputation, Aldrovanda has proven to be one of the most widespread of all carnivorous plant

species, growing across Europe and into Asia (including Japan before it was driven extinct there) and down

through Australia, where a rare red form is found. Aldrovanda even used to grow in the Hula Valley of Israel,

750,000 years ago.

CULTIVATING CARNIVOROUS PLANTS

Recently, Aldrovanda has been naturalized in several location in the

United States. This naturalization attempt has proven that, in favorable

conditions, Aldrovanda populations can explode. (One location in New

York State reports millions of individuals only a few years after a

handful were introduced). The difficulty, however, is in figuring out

where Aldrovanda will be successful. Ponds that appeared, upon some

inspection, to be nearly identical can see Aldrovanda successfully spread

in one, but die in another.

Empirical research has revealed that Aldrovanda grows best in 50%

Aldrovanda seed germinating.2

shade in oligotrophic lakes. Oligotrophic lakes have low-nutrient

content, resulting in low algal production and low nutrient

transformation. As a consequence, these lakes are often very clear, with high drinking-water quality. The

bottom waters of these lakes often have ample oxygen, which supports many fish species. Undoubtedly,

similar features are found in successful cultivation set-ups.

Given these requirements, it is not too surprising that

worldwide occurrences of Aldrovanda has slipped to under

100 populations in the wild, at the last count. Although areas

such as the northeastern United States and much of Europe

have largely rebounded from the effects of acid rain and

other pollutants, elsewhere, the detrimental effects of

pollution are still being felt. As a result, populations of slow-

distributing plants, such as Aldrovanda, cannot repopulate

areas rapidly without human assistance.

Although giving an exact formula for successful

cultivation of Aldrovanda is difficult, placing a thin layer of

sphagnum peat, or mud from a swamp, on the bottom of a

container topped by a thin layer of washed sand or gravel is

generally advisable. Small, reed-like plants and sedges, such

as Carex rostrata or Carex gracilis, should be planted in the

sand. A thin layer of leaf litter should be collected on the

bottom of the container. This set-up should result in a high

Rare Australian red form of Aldrovanda

carbon-dioxide (CO2) concentration, leading to low rates of

vesiculosa growing in cultivation.

decomposition and low algae content. The optimum water

depth should be about a foot (30 cm).

My standard growing guide for Aldrovanda follows:

✵

Media: A thin layer of sphagnum peat topped by sand and a layer of leaf litter from reed-like plants

should suffice. Water should be a depth of a foot (30 cm) or so. Some experimentation may be

necessary to achieve the clear, tea-colored water in which Aldrovanda grows well.

✵

Container Size: Containers should be fairly large but shallow. Most waterproof containers made of

plastic work well.

✵

Feeding: Aldrovanda will naturally catch many aquatic creatures and should not be fertilized.

✵

Temperature: Given the wide distribution of the species, it is important to know where the plants

being cultivated are originally from or under what temperature conditions they have been successfully

cultivated. Plants from tropical regions are unlikely form winter buds, or turions, and will die if

exposed to freezing temperatures, whereas more temperate plants will form winter turions and

NATCH GREYES

should be exposed to cold temperatures during winter. Essentially, growers will want to match the

native temperature ranges of the native areas.

✵

Dormancy: Dormancy is required for temperate plants but not for tropical plants. There is some

indication that plants from one region can and sometimes adapt to different conditions, but this is

difficult to do with a species as fickle as Aldrovanda.

✵

Propagation: Although Aldrovanda can be germinated from seed or divided much like aquatic

Utricularia, it is far easier (and less risky) to wait for the plant to divide on its own. A single plant can

produce over 30 new plants via natural division in the course of a summer, if conditions are right.