Barry Rice

- doing science on a terrestrial planet -

Focusing on U. gibba--the "U" stands for ubiquitous
(Carnivorous Plant Newsletter, 1994, 23:1, 19.)

A reason I enjoy growing Utricularia is that so many are extremely tolerant of differing cultural conditions and forgiving of mistakes and neglect. But ask me about growing aquatic species and I become edgy. After a few months or years, whatever aquatics I try to grow invariably wane and finally die. But there is a class of aquatic Utricularia which are easy to grow and are not so sensitive--the affixed aquatics. While these plants grow in water, they must be in contact with a substrate of soil to prosper. The lovely species U. gibba is such a plant.

The genus Utricularia is broken into two subgenera, Polypompholyx and Utricularia. In the latter subgenus are thirty-three sections and the largest (section Utricularia) contains thirty-four species including U. gibba. This section contains most of the familiar yellow flowered aquatics such as U. macrorhiza, U. vulgaris, and U. australis. Fortunately U. gibba is easily distinguished from most of these other species so identifying it is rarely a problem. I'll start this discussion of U. gibba by describing its form and habit so you can identify it yourself. Then I'll summarize how U. gibba has been confused with other plants in the past and lastly I'll include cultural tips. Describing any plant requires the use of some jargon and if you are confused by my usage refer to my U. calycifida article (CPN 21:1) and parts of CPN 20:1-2.

U. gibba grows in water only several centimeters deep. Examine a clump and you will see it consists mostly of green stolons which branch and intertwine to form a loose mat. This network comingles with the oozy muck of the pond bottom and anchors the plant underwater. Plants that grow like this are called affixed aquatics. Each stolon is several centimenters or more long and 0.2-1 mm thick. The stolons are terete (round in cross section). Rhizoids (small rootlike organs) may be visible hanging from the stolons especially near peduncle bases. They are only a few centimeters long.

Leaves are attached to the stolons at about 1 centimeter intervals and are small, only 0.5-1.5 cm long. Each consists of a pair of green hairlike segments attached to the stolon in a V-shape. Sometimes each segment branches so a leaf has four to eight tips. Viewed under a microscope, each leaf may be seen to bear occasional lateral teeth, each tipped with a little distinct spike (or setula, plural setulae). The tip of each leaf segment is also setulose. Setulose leaves are a common feature of species from section Utricularia. Bladders are moderate sized (1-2.5 mm long) and are found only on leaf segments (usually not more than a few per leaf). Under a microscope each is bare of appendages except some long bristles near the trap's opening.

Some clones of this plant yield few flowers, while others (the ones I retain in my collection!) produce many. Peduncles are usually 2-8 cm tall, less than one mm thick, and terete. They do not twine or branch. Up to two basifixed scales about 1 mm long may reside on each peduncle. These scales have an interesting shape--if you detached and flattened one it would be semicircular or almost rectangular. Each peduncle usually bears two to six flowers (but may have anywhere between one and twelve) arranged in a very loose spiral above the water level. The pedicels are 0.2-3 cm long, terete, and green like the peduncle. Bracts (one at each pedicel base) are shaped like the scales. U. gibba does not have bracteoles. Taylor tells us that submerged cleistogamous flowers can develop on short peduncles. I've never observed them but they might just be eluding me in the stolon mat.

The calyx lobes (the two sepals) are 1-3 mm long, the upper lobe being slightly larger than the lower. Both are approximately round or ovate with rounded tips and smooth margins. The corolla is typically large (2-2.5 cm long) and dwarfs the calyx but Taylor informs us that the flowers of some clones are as tiny as 4 mm long. Something that distinguishes U. gibba from most species of Utricularia is that the corolla upper lip is usually larger than the lower lip. The upper lip is circular or rounded-ovate and often clearly three-lobed. It is curved into a bowl-shape--like a clam shell--and is held vertical. The lower lip is also rounded in outline and has a prominent inflated palate bulge. The specific epithet gibba means bulge and refers to this. The long, straight spur is cylindrical or conical and is pressed close against the underside of the lower lip. The lower lip is either flat or may drape downward on either side of the spur. The spur often pokes out from under the lower lip. Its tip may be bifid. The entire corolla is yellow, often with red or brownish veins on the inflated palate bulge--standard coloration for most species in section Utricularia. The flower is odorless and lasts for several days to a few weeks before withering. For me, the whole effect of the flower is that of a baby bonnet--the upper corolla lip marks the baby's hood and the lower lip and spur represent the jowels and protruding nose of the sadly unattractive infant.

thumb Like the CPer's weed U. subulata, this species has an enormous range. It grows on every continent of the world (except Antarctica) and is limited only in preferring warm climates. It occurs in most of the U.S.A., even Hawaii, except the plains and rocky mountain states (as usual it is not found in my own CP-deficient state of Arizona). It flourishes in all kinds of freshwater wetlands and Taylor even observed it growing as a semi-epiphyte. While it much prefers to grow in shallows it can occur as a free floating aquatic but rarely flowers in this condition. I have seen it on Vancouver Island, Canada, growing in this form. In more suitable habitats U. gibba flowers during the warm time of the year, or year-round in tropical regions.

U. gibba is mentioned by Taylor as being one of the several most variable species in the genus--not too surprising considering its large range. The chief variation is in the size of the flower. Since Linnaeus first included the species in his Species Plantarum in 1753 more than sixty varieties of U. gibba have received temporary species status, four times even in genera other than Utricularia. During his career Taylor recognized several of these putative species but by the time he dealt with the group in his monograph he consolidated them all into U. gibba. I recommend you read the discussions of U. gibba and U. striata in his monograph for the details of his arguments if you are interested. The essence of his reasoning is that while some forms of U. gibba have large flowers and others bear small flowers, a continuum of plants with intermediate corolla sizes also exist and these plants blur the distinction between proposed species or even subspecies within the species U. gibba. The widely cited species U. exoleta and U. obtusa are both absorbed by Taylor's treatment into U. gibba.

The history of U. gibba in the U.S.A. is particularly confused. Biologists have tried to recognize a complex of three species they called "U. gibba," "U. biflora," and "U. fibrosa"--all with similar flowers. The main difference between "U. gibba" and "U. biflora" was considered to be the size of the lower corolla lip. For example, an old key in CPN 2: p66 by Kondo describes the lower lip of "U. biflora" as 8-10 mm long and that of "U. gibba" as only 5-6 mm long. Also the name "U. gibba" was applied to specimens which had short, blunt spurs, while "U. biflora" was used for plants with longer, more slender ones. But many intermediate cases indicated these divisions were artificial. Lastly, it was thought "U. gibba" usually had fewer terminal leaf tips than "U. biflora." Again this was found to be unreliable and poorly correlated to flower size. So "U. biflora" and "U. gibba" were combined into the species we know today as U. gibba. And how does "U. fibrosa" fit into this? Looking into the old literature, Taylor deduced two things. First, the original description of "U. fibrosa" by Walter was actually an account of U. gibba, so "U. fibrosa Walter" is a synonym of that species. Second, Taylor found that in the intervening years biologists mistakenly began calling a different species "U. fibrosa," thinking it was the plant Walter described. This additional species had been described already under the name U. striata, a name Taylor adopted in his monograph. So in summary, sometimes the name "U. fibrosa" refers to U. gibba and other times it refers to U. striata. The easiest way to tell them apart is that U. striata produces two types of leaves--its leaves are dimorphic. One type of leaf is part of a stoloniferous and subterranean network much like U. gibba and the other type of leaf is foxtail-like and floats freely in the water. I observed fine specimens of this species in Lake Oswego, New Jersey, and in my ignorance reported it in CPN 18:3:p70 as "U. fibrosa." Excellent drawings of U. gibba and U. striata are in the dicot volume of Aquatic and Wetland Plants of Southeastern U.S., by Godfrey and Wooten. In this work U. gibba is portayed as U. biflora, Figure 323, and U. striata as U. fibrosa, Figure 315d. So there it stands--time to make annotations in the margins of the Utricularia sections of your reference books! And when in the midst of Utricularia confusion in the field or greenhouse, it is reassuring to your ego to know that professional botanists have been just as baffled.

For a quick reference, if you are in the field in North America and you find a yellow flowered aquatic Utricularia with a very large upper corolla lip (and no floats as in U. inflata or U. radiata), examine the leafy parts very carefully to see if there is only one kind of leaf. If the leaves are dimorphic, with some being big feathery foxtail-like leaves, then you have U. minor, U. striata, or U. foliosa. Also if possible, see if you can find any ripe seed capsules opening. Do they open by a vertical spit that divides the capsule into two equal halves? If so, chances are you're looking at U. gibba. But for a good key, certainly more complete than the information in this paragraph, look to CPN 20:1-2.

As I mentioned above, affixed aquatics are infinitely easier to cultivate than suspended aquatics. Suspended plants are much more sensitive to the chemical balance and temperature of the water. Also algae overwhelm the plants and treatments for it often kill the Utricularia. In contrast, my technique for affixed aquatics is easy and nearly trouble free. For a growing container, you need a sturdy undrained pot or tub at least 7-10 cm deep and about 15 cm or larger in diameter. In this container lay 2-3 cm of premoistened peat moss, peat-sand, or Sphagnum. Add a top dressing of a few centimeters of washed sand. The sand layer weighs down the peat so the water stays clear. Also since sand is lighter colored than peat it absorbs less sunlight and the water will stay cooler. Carefully add enough pure water to submerge the sand a few centimeters. If your clone of U. gibba is sturdy it may be planted immediately but I usually prepare a new tub a few days before I need it. This is to let the chemistry of the water equilibrate before introducing the plants.

Planting the Utricularia is trivial. Make a depression in the sand layer and wedge the plant into it. Then anchor it with sand, allowing some parts to still get light for photosynthesis. Thereafter keep the water table a few to several cm above the top of the sand. The plant will grow rapidly, making some stolons that wind through the sand and peat layers and others that float freely in the water. If you insist on growing the plant in deeper water or as a suspended aquatic it will not flower. When adding water take care not to disturb the sand layer or else you may allow mucky black peat to bubble up and dirty the water. The plant prefers full sun and can survive temperatures between 0-40°C (32-104°F) but you should try to emulate the climate of your specific clone's geographical home. I usually repot in early spring because after a winter of slowed growth algae start to clog the U. gibba and irritate me. To repot I pull out the mass of Utricularia and replant a portion in a new container using the method I described above. The remainder is sent to other growers. By summer the tub is dense with growth and a profuse display of flowers. Strangely, my most floriferous clone never produces seed but clones which rarely flower often do produce seed.

I never fertilize U. gibba because it would probably result in an algal bloom. If you live near a very pure pond, you may want to take a few spoonfuls of pond water and add it to your U. gibba. The natural fauna will help feed your plant's traps, and may help graze the algae. But beware, it could also introduce pests such as snails which might eat the Utricularia! The only pest I have ever had on this plant are aphids attacking flower peduncles but removing the few infested inflorescences eliminated the problem immediately.

I am a reasonable person, so when I show newcomers my greenhouse I understand when they get a chuckle from seeing the tubs of my aquatic plants. One friend summed it up well when he said, "You're growing mud!" That is when I show them a container of U. gibba. While the other aquatics may not be doing much except looking mucky, U. gibba is almost always putting on a great display of lovely blossoms. It is a gratifying plant--grow it!


10 November 2007