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.
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!