Corkscrew plants

What they are

From above, a corkscrew plant looks like almost nothing: a flat rosette of small green leaves, spoon-shaped or strap-shaped and a few centimetres (an inch or so) across in most species, with thin stalks of small yellow, violet or white flowers much like a bladderwort’s. Everything interesting is below the surface. The plant has no roots. In their place it sends down pale, non-green leaves that are the traps, and that anchor it and feed it.

Each trap is a hollow stalk that swells partway down into a digestive chamber, narrows again into a tube, and then forks into two arms, each twisted into a helix like a corkscrew. A slit runs the length of both arms. Protozoa, nematodes and other soil animals enter through the slit and meet rows of hairs pointing toward the chamber; they can move up the arm but not back, and end in the chamber, where glands digest them. It is an eel trap built from a leaf, and traps can reach 20 cm (8 in). What draws the prey in is unsettled.

The genus has about 29 species in the Lentibulariaceae, the family of the butterworts and bladderworts, and is the bladderworts’ closest relative. It has one other claim to fame. Some South American species have the smallest genomes of any flowering plant, about 61 million base pairs in Genlisea tuberosa and 64 million in some G. aurea, while other species in the same genus have genomes some twenty-five times larger. The record was long credited to G. margaretae, a figure that turned out to come from a mislabelled G. aurea. Carnivory in the genus was only demonstrated in 1998, though Darwin suspected it in 1875.

Where they grow

Corkscrew plants grow in tropical and subtropical Africa and Madagascar and in Central and South America, with the oldest lineages in the mountains of Brazil. They live in wet sandy or peaty ground poor in nutrients, from seasonally flooded grassland to the sandstone tepuis of Venezuela, usually beside sundews and terrestrial bladderworts. A few are semi-aquatic. The habitat dictates the pot: warm, bright, permanently wet, and deep enough for the traps.

The range in cultivation

There are no groups to learn: every species in cultivation accepts the same conditions. G. hispidula, from Africa, is the most widely grown and the easiest to multiply; G. violacea, G. repens, G. pygmaea, G. aurea and G. lobata from South America are the others a specialist nursery is likely to list. G. aurea covers its leaves in clear mucilage, which is normal, not a disease.

Growing them

Light

Strong light up to part sun, or a grow light. They grow in shade but flower better in bright light; growers keep them under fluorescent tubes or 50 percent shade cloth.

Water

Pure water only, and plenty of it, with the level at or a little above the soil surface. An undrained container works, as does a net pot or mesh basket standing in a jar of water, which lets you lift the pot out to look at the traps.

Growing medium

Sphagnum peat with a high proportion of sand, up to three or four parts sand to one of peat, or long-fibre sphagnum, or equal parts peat and sand; they are not fussy. Depth matters more: the traps grow far longer than the rosette suggests, so use pots at least 10 to 12 cm (4 to 5 in) tall. Live sphagnum outgrows the plants and buries them.

Temperature

Tropical. Growth is fast at about 18 to 35 °C (65 to 95 °F) and slows below that; keep nights above about 15 to 16 °C (59 to 61 °F). Frost is fatal.

Dormancy

None. G. pygmaea forms tubers to survive a dry season in the wild, but in a constantly wet pot the plants grow year-round.

Feeding

Not needed; the traps catch the protozoa, rotifers and nematodes that live in any wet medium. A few grains of dry fertiliser in the water of a net-pot system help, but a pinch is too much and brings a smothering growth of cyanobacteria; water fleas for plants grown in water, or an occasional foliar mist, are alternatives. Fertiliser in the soil can kill this group, so if you feed at all, feed the water lightly and watch for algae.

Common mistakes

Letting the pot dry, which kills them as it kills a bladderwort. Keeping them cool over winter. Burying the rosette under moss. Treating the traps as roots and tearing them at repotting. And overfeeding under bright light, which produces slime rather than growth.

Which to start with

G. hispidula first: forgiving, often in flower, and grown into a new plant from any leaf laid on wet sphagnum. G. violacea second, a smaller plant with a different flower that needs trap cuttings instead of leaf cuttings but is otherwise identical in care. If you already grow Utricularia sandersonii, you can grow both.

Going further

Growing them in a net pot that lifts out of its water lets you watch the traps, which few carnivorous plants allow. Multiplying them is simple and is set out in the propagation entry. The natural next step is the epiphytic bladderworts, which share the family, the rootless habit and the flowers but ask for cooler, more humid conditions.