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Re: Ceratophyllum demersum - or is it submersum?

>From: Susi Barber <wanderer35 at operamail_com>
>Subject: Ceratophyllum demersum - or is it submersum?

>I have Ceratophyllum submersum (Tropical Hornwort), 
>which has no roots, and is a floating plant.   

>"Demersum" I think means it should be grown emersed, 
>ie in the air, not underwater - experts please

Well, I'm certainly no expert, but the Latin origin of
'demersum' is 'demergere,' and that which is demersal
is found on the bottom.  

There are apparently two varieties of Ceratophyllum
demersum.  One originating in Mexico, the other native
to the United States.  The Mexican variety of the
plant has thicker stems and longer leaves.  I believe
this is the flavor shown in Tropica's database:


The U.S. flavor has more delicate stems and shorter
leaves placed farther apart on the stem.  I have what
I believe is the one native to the U.S.  It is
definitely the one pictured on the left at the
following location:


The plant is popular in pondkeeping circles for algae
control.  My 150 gallon puddle is nearly over run with
it.  The plant has an almost mythological reputation
for warding off floating algae.  My pond has fantastic
water quality, but it's also incredibly overplanted.

> Anyway, they need a lot of light - losing leaves
> suggests to me not enough light.  

I concur--the plants that are doing well are in the
best lit area of the tank.  The ones that were not
doing well were in shaded areas.  The pond these came
from gets about 6 hours of raging, Gulf Coast sun.

> It should also be floating at the top of the tank
> if it is "submersum", rather than anchored to the
> bottom of the tank with a stone.

I have it growing both ways.  In the pond, I have the
stuff growing as a free floater and anchored to the
bottom.  I also have it anchored to the bottom to
camouflage the lily pots.  I left some floating
because dragonflies favor it for egglaying.   

In the tank, I have it all anchored.  Light conditions
aren't anywhere near as intense there, and won't ever
be.  But some of stuff is doing well.

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