Barry Rice

- doing science on a terrestrial planet -

U. sandersonii--a Siren from Utricularia
(Bulletin of the A.C.P.S., 1994, 13:1, 6.)

Of all the genera of carnivorous plants, Utricularia reigns supreme. For in addition to containing more species than any other carnivorous genus, it is also the most widespread in global range. Indeed--it is likely that the the carnivorous plant in the wild closest to you at this moment is a Utricularia. Yet for its preeminence, why is the genus so under-represented in cultivation? Surely part of the answer lies in size. Most species have small above-ground portions--none of the downward pointing hairs, waxy cuticles, or droplets of adhesive mucous, all of which are the meat and drink (especially meat) for the carnivorous plant grower. Another reason the genus is so often neglected in collections relates to sheer horror factor. Part of the perversity of the carnivorous plant grower is the thrill of revulsion and fascination derived by seeing a plant strike back at the invertebrate world which is so often its foe. But Utricularia do their dirty work in the dirt or underwater, so the grower is (unfortunately) spared a view of the prey's horrible demise. These handicaps are well illustrated by the well intentioned but rather pathetic compliment Adrian Slack (1979) paid to plants in the genus: "The tiny grass-like leaves of some of these species are often hidden by moss growth....their continued existence is at once evident when they flower."

I recall first reading Slack's words when I was in the early stages of my carnivorous plant career. I thought, "What a silly plant that is! I want to see my plants all the time--preferably in gruesome action--and not just when they are flowering." But with time I have become enlightened. It is true that the plants are not big. (The leaves of U. longifolia reach a meter in length only extremely rarely, and the largest U. macrorhiza branches I have seen in the wild were barely 1.5 meters long.) It is true that the plants are not particularly hideous in carnivorous action. (Although seeing U. striata drown struggling mosquito larvae by trapping their heads once gave me claustrophobic dread. And supremely dreadful was watching a worm, held at each end by two bladders, struggle for longer than a week while it was slowly digested alive.) But a great prize awarded the horticulturist is that after the beastly bladders have glutted their appetites, and the plants have grown sufficiently large, they salute the grower with a display of flowers, the beauty of which is unbeaten by any other carnivorous genus. Truly, people grow Utricularia not only for their horrific carnivory, but also for the incredible diversity of flowers, the surprising variation of leaf morphology, and finally the horticultural challenge presented by a huge genus containing terrestrials, epiphytes, suspended aquatics, affixed subaquatics, lithophytes, and many other types of plants.

thumb The plant U. sandersonii is a delightful species. It is in the section of the genus called Calpidisca, which also contains nine other species, including the frequently grown U. livida and U. bisquamata (the latter is often incorrectly called U. capensis--a botanically invalid name). Keying species of Utricularia is often a subtle or technical process, but this is not the case with U. sandersonii--the flowers are absolutely unique. No other species is even remotely similar, so if you have a plant that looks like the photograph, its identification is not in doubt. Perhaps the species which is most closely related is U. livida, but it can easily be distinguished from U. sandersonii because its upper corolla lip is not split into the two bunny-ears that are so entertaining on U. sandersonii. The leaves of U. sandersonii are unlike those of the common weed-species such as U. subulata, U. bisquamata or U. lateriflora. They are cuneate--a narrow wedge shape that usually flares slightly before terminating abruptly.

Taylor (1989) writes that these plants come from a small area in South Africa where they often grow on wet, vertical rock faces, at an elevation of 210-1200 meters. In spite of these peculiar conditions in the wild, the plant requires no special cultural methods. I use a method that works for almost all the tropical Utricularia except aquatics and semi-aquatics, or the large species that do better in live Sphagnum. When CPers refer to "standard Utric culture," the following procedure (or close to it) is usually what is meant. Use either pure dead milled Sphagnum or a 2:1 peat-sand mix in a 5 cm (2") pot. I use water purified by distillation or reverse osmosis. I know some growers are fortunate enough to be able to use tap water, but my Arizona tap water contains far too many dissolved chemicals. The soil should be permanently moist--I keep my pots in trays filled with enough water so the water table is just a few cm beneath the soil surface. Keep them warm year round, around 20-30°C (68-86°F). If the plants are kept too cool they grow extremely slowly, while if overheated the flowers are pale in colour and do not last as long. Since they are found in shady places in the wild I give them medium light. While this means some shade in the greenhouse, the light available in most 4-6 fluorescent bulb terrarium set-ups is fine. In good conditions, U. sandersonii grows quickly. After only a few months it will cover the surface of a 5 cm pot with its little leaves. It is easy to propagate--carefully detach from the mother pot a hunk of leaves, stolons, and bladders, and plant it in a new pot. In time you will be rewarded with a dense display of lovely flowers. Despite a few half-hearted attempts at selfing and cross pollination, I have not been able to yield seed from my plants.

There are more than two hundred species of Utricularia, and the majority are in cultivation. Once you start to grow them, there is little chance you will ever stop. But first you must modify your motivation for growing plants--don't restrict yourself to carnivores like Drosera that bear modified leaves. The strength of Utricularia is in its flowers--appreciate that aspect of this genus. And what better choice is there to introduce you to the genus than the easily grown and floriferous U. sandersonii? The beautiful siren calls to you from its slippery home of water-splashed rocks, the trap is set and the unwary grower is easily seduced--all you must do is follow its song!

Slack, Adrian. (1979). Carnivorous Plants, MIT Press, Cambridge.
Taylor, Peter. (1989). The Genus Utricularia, Royal Botanic Gardens, Kew.


10 November 2007