Barry Rice

- doing science on a terrestrial planet -

Growing Terrestrial Genlisea
(Carnivorous Plant Newsletter, 1994, 23:2, 36.)

Late in the summer of 1991 I received in trade a plastic bag filled with live Sphagnum. Carefully exploring through the strands I was thrilled to discover that the object of my desire had survived the shipping ordeal, and I finally had an opportunity to grow a Genlisea. My new acquisition was smaller than a grain of rice, so I planted it immediately. Some species of Genlisea are aquatics and others are terrestrials. I wasn't sure of my new plant's preferred habit, so to be safe I embedded it in a loose mix of live fluffy Sphagnum just a few cm above the water table. The plant is now thriving and has taught me many things about growing species from this genus.

Despite its reputatation as a difficult plant, my first species (Genlisea hispidula) is very accomodating. I grow mine in live or unmilled dead Sphagnum. A more densely packed medium (such as a peat or sand mix) may not allow tiny aquatic creatures to swim into the traps. I keep the water table near or just below the moss surface. Of course, use only pure water for these plants. I grow mine under 50% shade cloth. The spatulate or cuneiform leaves (up to three cm long each) are arranged in a rosette. The plant sometimes becomes covered by heads of growing Sphagnum. When this happens I pull the strands back to keep the plant from becoming buried. Kept at about 18-35°C (65-95°F) the plant will grow quickly. Cooler than this and its growth slows. I suspect a frost, however light, would be the end of your Genlisea. Fertilizer is not necessary so I have never used it.

When the rosette matured it produced an unbranched scape 20 cm tall with several flowers (Figure 1). As I examined the flowers something kept nagging me--I felt they reminded me of something but it wasn't until I was composing this article that I realized what it was. The arching lid-like upper corolla lip, the strange lower lip, and the sub-conical spur conspire to mimic the lid, peristome, and basin of a Cephalotus pitcher (But I am not suggesting the flower is carnivorous!). Carefully following Peter Taylor's key in CPN 20:1, p22, I was easily able to identify the plant as G. hispidula. I was slightly surprised the plant was correctly identified when it was sent to me--a real rarity with the related genus Utricularia!

thumb The carnivorous traps on this genus are produced below ground from the rosette base and are shaped like an inverted "Y" a few to several centimeters in total length. Excellent line drawings of the traps can be found in Lloyd or Slack's first book. Midway between the trap's point of attachment and the bifurcation is a tumerous swelling--the utricle. This digestion chamber is the ultimate destination for wayward rotifers. A tube connects the utricle to the trap bifurcation. Each of the two branches of the trap is tightly twisted into a helix. A slit spiralling along the length of the helix allows free-swimming organisms into the twisted canal. Once inside, the creatures are constrained to swim along the inside of the canal by that old standbye in plant carnivory (and something I feel I have read countless times), inward pointing hairs. These hairs allow the creatures to swim only towards the trap's utricle. Occasional columnar structures called prop-cells connect the walls of the canal and keep them spaced at a fixed, optimal separation. There are many unanswered questions regarding the function of the traps. After this article I present an order of magnitude calculation to explore if Genlisea suck water through their traps in order to accentuate their efficiency. But despite our poor understanding of the mechanics of the Genlisea traps they are effective. The utricle of older traps are clearly discolored by the internal accumulation of digested material and detritus.

A more recent addition to my CP collection is G. violacea. This plant is smaller in all respects than G. hispidula, with petiolate elliptical leaves 2 cm in total length. In flower it is much different, and resembles from the front a small Viola flower. The flowers are spaced only a few centimeters apart, and are long-lived enough so that several flowers are in full bloom in a lovely spray at all times. It grows well using the same culture as for G. hispidula.

thumb These species, especially G. hispidula, are easy to propagate. For vegetative propagation use cuttings from leaves or traps. Some even report success using scapes! The cuttings should be partially buried in live Sphagnum. For leaf cuttings, remove as much of the petiole base as possible, and anticipate the new plantlets to develop anywhere on the leaf. Leaves can be cut into pieces for more plantlets. If scape cuttings actually work, I expect the new plants would develop from the peduncle scales. This species will produce viable seed even if not selfed. When the seed capsule matures and splits (see Taylor's figure 1-5, CPN 20:1, p34, for the remarkable details of capsule dehiscence), sprinkle the seed immmediately on wet Sphagnum. Germination will occur in a few weeks. Treat cuttings and seed as you would mature plants. The species G. violacea is a little more challenging. Selfings don't produce seed, and leaf cuttings have never struck. I owe a thanks to Gordon Snelling who first told me about the success of trap cuttings. In fact when I have examined the traps still attached to a plant I have noticed parts of the traps (especially the tips) may develop adventitious leaves which grow to the soil surface and produce new plants.

I hope I have whetted your appetite for these remarkable little plants. In attention to detail their traps are the most complex of all the carnivorous plants--second perhaps only to Utricularia. Their flowers are delightful, and when the species discussed here reach flowering size they continually produce scapes all year. And the plants are easy! If you can grow terrestrial Utricularia then you can grow the plants I described here. I have never grown an aquatic Genlisea, and anticipate they may be more exacting in their treatment (as is the case with most aquatic Utricularia). Very recently I have obtained specimens of G. repens and a plant which may be G. pygmaea. Time will tell how much luck I have with them. Good luck with yours!

Postscript: Both G. repens and G. pygmaea have acclimated well to greenhouse culture, and can be grown as G. hispidula. Both are very small plants, however, and multiply very slowly.


10 November 2007