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Duckweeds and Other Aquatic Aroids

  • Subject: Duckweeds and Other Aquatic Aroids
  • From: Theodore Held <oppenhauser2001@gmail.com>
  • Date: Tue, 20 Jan 2009 10:48:32 -0500

Beth, and Others,

Duckweeds are certainly aroids that will grow in aquaria. Spirodella are easier to control, but are not quite so invincible as Wolffia or Lemna. In my experience, the smaller forms (Spirodella, alone excluded) are a royal nuisance. They tend to spread everywhere and are amazingly tough. One good thing, however, is that a single goldfish can clean up the whole mess in a few weeks or less.
The trouble with duckweeds, horticulturally, is that they have flowers so small that you'd be hard-pressed to find them or even see them, even if you look. Mostly what you see is a little glob of green, with or without a pitiful little root, possibly a pair of roots. None of these appearances are endearing to me.
One interesting feature of duckweeds and Pistia is that they are among the few species of aroid that can be seen easily from an airplane at 10,000 feet. I remember flying out from Miami after last fall's show and noting the big, uniform sheets of aroids floating tranquilly on inshore water. Very distinctive and far greener than any other massed plants. They are nearly luminous.
One thing I forgot to mention in yesterday's note on Pistia is that they are, size for size, one of the FUZZIEST plants I have ever seen. Challenge to the list: Is there another aroid that comes close to a Pistia for fuzziness? The leaf surfaces are covered with proportionally very long hairs of leaf tissue. Even the flowers are enclosed in spathes that look like tiny fur coats. This is one reason Pistia are so incredibly buoyant. Try to sink one and you will be amazed. Duckweeds, in contrast, are smooth and not nearly so unsinkable. In a closed glass container, the leaf hairs of Pistia condense water and create spherical water droplets perched delicately on leaf surfaces. In the "wild" Pistia will be found to be covered with these little jewels after a rain. In the current scientific lingo this effect is known as "water on a duck". But I think ducks cheat a little and have lightly oiled feathers. Pistia are the pure phenomenon: just a failure of water to sink down between the hairs and wet the leaf topology.
One other physical effect that may arise in Pistia stems from the fuzziness. That is, because of the huge surface area encompassed by the leaf hairs, I bet that transpirational water evaporation is likely extreme. The surface area of a mass of Pistia has got to be many multiples of the effective surface area of a similar patch of duckweed. Maybe this could be used for drying of flooded areas or other applications requiring huge evaporative strength. At the same time, the cooling effect of masses of Pistia and their evaporative water losses could be used as a form of "green" air conditioning. (?) Just a couple of speculations.
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