Sunday, November 16, 2008

Who’s been eating my Mosquitos?

Yellow Bladderwort  
Utricularia gibba ssp exoleta (Utricularia exoleta)
A little bird gave me some of these lovely plants for Christmas. Literally.
They appeared in the Gardner pond one year.
For some time, I paid no attention to the plant, which was just a mass of fine, entangled green stems, with no obvious beginning or end, top or bottom, roots or leaves. It was peppered with little black lumps, smaller than a pinhead, and floated submerged, neither very attractive, nor particularly unattractive. When the first flowers appeared in a shallow corner I was slow to connect them with the floating plant.
They were very pretty, bright yellow, measuring a centimetre across, and standing 6cm above the water on fine little stems. I was charmed by them, but had considerable difficulty making an identification. When I eventually discovered what the plants were, I was delighted to know that this is one of the world’s more sophisticated carnivorous plants!
The “black lumps” were the bladders, which provide the plant with enough nutrients for it to be able to live in quite nutrient-poor water. I’ve discovered that they are very effective at keeping my bowls of water-plants free from mosquito larvae. They don’t get rid of visible wrigglers, but water with this plant in it remains wriggler-free, so it must be consuming them fresh out of their eggs.
Some research told me that the bladders in “hunting” mode are rather flat, with a little round entrance above which a few trigger hairs protrude. Nearby glands secrete a sugary bait. If a tiny creature touches the hairs, the bladder springs into its full ball-shape sucking in water and the prey. The door snaps shut, and the water in the bladder is pumped out again through some little glands (taking 30 minutes to 2 hours). By then, the bladder has returned to the flattened shape, and opens its door for more prey.
Meanwhile, the previously-caught prey is slowly being digested to feed the plant. Bladders which have fed successfully are black, and I notice that my plants’ bladders don’t have much luck in winter, when I suppose the bladderworts have to live on photosynthesis alone.
Apparently mosquito larvae and even fish fry can be captured by the larger bladderworts – and the little dots on my plants seem to be large by bladderwort standards. They don’t seem to bother the goldfish or frogs. (I have no native fish, so don’t know whether these are affected.)
Although these bladderworts can live in fresh, still water of any depth, they need shallow water to flower. The water’s pH should be 6.3 to 6.8 - rainwater is fine. A ledge at the edge of a pond, or a dish or bowl part-filled with soil or sand seems to suit them, and a warm, sunny site (they like to be between 18 and 29°) keeps them flowering well, but they survive the winter so long as their water doesn’t freeze.

How to “Source” Bladderworts.

Acquiring some for yourself may be a simple matter of providing a suitable habitat, and waiting for the birds to provide. I have a rather large birdbath, in which I’ve put some sandy soil which slopes from just above water level to 5cm deep, so plants can choose their own depth.
Other gifts from the birds have taken root on the higher soil, making a healthy little ecosystem and a very pretty garden picture. Magpies bathe in the deeper water, but this doesn’t worry any of the plants in my pretty dish-full.

Other Gifts from the birds.
We have never been able to stop the drips from the solar hot water system on our roof. The people from Solarhart assure us this is normal. I hate letting it go to waste, though, so have a birdbath/water garden underneath it, which I only need to top up with rainwater in very dry weather.
It now has four lovely thing growing in it, all bird-given.
Triangular Club-rush, Schoenoplectus mucronatu
This elegant “decorator” plant it is so good to cut for a vase when it’s in flower (Sep - May). The light green triangular stems can get to 50cm high, but are much less in the restricted soil of my bird-bath. 2cm from their tips they put out - sideways - a neat bunch of their little flowerheads - the golden-brown cone-like “clubs” which give them their name.
Left to themselves in a pond or dam they form a thicket in the shallow water and provide good breeding sites for frogs. Though they seed freely, they are not particularly invasive. In my own dish, I find a once-a-year (early spring) clean-out and re-plant keeps the arrangement looking good year-round.

Trailing Pratia, Lobelia pedunculata (Pratia pedunculata)
I am unsure whether this plant came to me from a native source, or from a garden, as I am not aware of it as a wild plant in the area.  It as it is an easy native plant to buy, and mine is a lovely (commercially desirable) shade of blue, so perhpas it's not a real native. On the other hand, water plants tend to have a very wide native range, so perhaps it can qualify as a valid addition to this blog about local native plants..
The plant needs constant dampness for success in full sun, and rewards us for providing it with a generous sprinkle of its blue flowers from October through to April.
It’s said to tolerate light frosts.

Small-leaved Pennywort, Hydrocotyle peduncularis
You see this one on lists of plants recommended for frog-gardens. It has dainty little (1cm) leaves, almost circular, with five scalloped lobes. They make a pretty carpet of soft, fresh green at the water’s edge (both in and out of the water), and mix happily with other small plants such as Lobelia and Utricularia.

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