[APD] RE: wax cuticle on flooded succulent plants

["Steve Pushak" <teban at powersonic_bc.ca>]

Stephan Mifsud wrote:
> Steve P's Hypothesis: "plants which adapt to
> seasonal flooding need to have the ability
> to grow a thin or absent cuticle"
>
> exceptions ... Crassula vaillantii, a very small
> succulent,... germinates naturally underwater ...
> in very shallow pools with regular
> drying and flooding according to rain fall. It may be
> submerged for a few
> weeks, completely emersed for another week, in the baking
> Mediterranean
> sun, then submerged again. There is no time to thicken/thin a
> cuticle. This
> is obviously always present-yet it grows very well submerged.

Here is a picture:
<http://www.uib.es/depart/dba/botanica/herbari/generes/Crassula/vaillant
ii/>

These leaves are typical for a terrestrial succulent. We should probably
classify it as slow growing. "Growing well" is relative.

Perhaps it is using stored reserves during this submerged time?

Can we tell if it is photosynthesizing submerged?

If the leaves are waxed and the surface area to mass ratio is low as is
the case for a succulent, then it would have a hard time to absorb
enough CO2 from the water. Perhaps it is utilizing carbonate instead!?

Another possibility is that it is getting CO2 underground; but I think
this is unlikely. A substrate high in CO2 would be strongly reducing &
this would not be a good habitat for a plant with limited oxygen
producing potential.

Do you have this plant growing submerged for a long period of time? Does
it require CO2 fertilization to survive?

Does it cause pH to rise over time when CO2 is not supplemented? This
would indicate carbonate utilization.

How do we know how thick the epicuticular wax layer is? Are you judging
by appearance or analysis/measurement of the layer?

I could not find any picture of Elatine gussonei.

Palaearctic:
<http://encyclopedia.thefreedictionary.com/Palaearctic>

Stephan has correctly pointed out that "seasonal flooding" could include
temporary flooding in very arid regions where the plant can survive in
alkaline water using carbonates or stored reserves until the water
evaporates & then it has to rapidly resume its succulent nature,
conserving water evaporation. In this case, it would not have time to
grow different leaves as Crypts do. I don't think there is any way for a
plant to loose its waxy cuticle once it has it nor to rapidly form one
on a flimsy underwater leaf.

Steve P

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