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Emerse grown aquarium plants: Internet legend?

It's often repeated on Usenet that certain kinds of aquatic plants are 
actually grown emersed and then sold in aquarium stores. This has the 
ring of another Internet-legend to me. Does anyone know this for a 
fact?

I suspect that a great many aquatic plants are actually grown in ponds 
outdoors in places like Florida using filtered sunlight which may be 
the reason why they have a particular leaf shape or coloration. Most 
transitional aquatic plants have a different leaf morphology 
(structure) for submerged growth than emersed. The submerged leaves do 
not have a thick cell covering and loose their internal fluids due to 
evaporation. Those leaves quickly wither and die when exposed to air. 
Emergent leaf growth has a protective wax-like covering (cuticle) 
which prevents this to a large degree however the transport of 
nutrients occurs because of the transpiration stream driven by gradual 
evaporation in the leaves. Under water the transpiration stream is 
much slower (no evaporation) so nutrients have to be absorbed by the 
leaves and they can't due to the cuticle (if an emergent leaf). Emergent
leaves aren't very suitable for under water growth. If you look closely
at them, you'll find a waxy kind of coating which is not present in
underwater leaves.

I think there are some kinds of plants (marginals that live in bogs 
etc.) which can survive and grow very slowly underwater such as 
Alternanthera and Lobelia. I think you -might- be able to get Lobelia 
leaves to survive out of water but I've seen Alternanthera leaves near 
the surface get desiccated when the water level goes down. Once the 
growing tip gets above the surface of the water, they seem to grow a 
different kind of leaf. Its often said that Alternanthera sold in 
stores is grown emersed and I'm more willing to accept that than sword 
plants. Very seldom do you get an Alternanthera in a store which can 
survive and grow in the aquarium but once you do get a specimen, you 
can grow it fairly well especially in fertile substrate with 
higher light levels and CO2.

Crypts are another plant which are transitional and have different 
morphologies emersed and submersed. We suspect that some of the 
triggers for Crypt meltdown are actually signals to the plant in 
natural circumstances that the dry season is approaching and it may be 
drawing reserves into the roots in preparation for regrowth emersed 
leaves. Interestingly, the Crypts which don't suffer much from 
meltdown are those that live most exclusively in water such as C 
crispulata!!

Sword plants are so very easy to grow under good conditions that I 
would be surprised if they are cultured emersed. Has anybody seen it 
done? Several types of Echinodorus such as melon swords or E osirus 
develop large floating leaves; E cordifolius gets large leaves which 
will rise right out of the water however these plants don't look very 
attractive in aquariums like that so I suspect they prefer to sell 
them small and innocuous looking. I always make sure to cut off leaves 
of my black melon sword when they get to the surface or it seems to 
only grow those type of leaves. I gave up on E cordifolius because it 
took over the aquarium and was threatening to expand into other rooms 
of the apartment! ;-)

Steve Pushak teban at powersonic_bc.anti-spam.ca 

Visit "Steve's Aquatic Page" http://home.infinet.net/teban/
 for lots of pics, tips and links for aquatic gardening

Aquatic Gardeners Association