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Re: alleopathy

> Since higher order plants did evolve, they must have developed some way of
> preventing algae from attaching to their surfaces and thereby suffocating
> them or causing them harm in some other way.

Where did land plants evolve?

Some of the first "plants" were likely aquatic, see recent publication in
Aquaphyte. Chara or something similar was a likely ancestor. But the main
method for out competing is through light with aquatic plants. Most plants
are terrestrial in ancestry that we keep and many don't live in submerged
permanently. Most are the whales of the plant world returning to the sea
after evolving on land with stomata etc. One land plant does not have any
stomata I know of(Stylites).

Realize that aquatic plants are generally weeds that run across the surface
of the water. Rather than saving a leaf and spending the energy, it's easier
to fragment/grow a new leaf and pile up. The dead leaf and leaf litter will
block out the light and reduce competition.
> Because plants are relatively inanimate and most can not remove or prevent
> algae from attaching to their surfaces by any physical means, they must
> possess some other method to achieve this.

They must? There are other factors, temp, time, desiccation, wind, current
etc. The aquatic environment is highly variable.
Plants can shed their leaves also. Poor plant growth with
Hygrophila/Ludwigia will lead to this. A leaf can simply become inactive,
get covered with algae and simply be a nutrient source for the new growth up
above. The stem often is still attached to the substrate but the plant may
lose all it's lower leaves.

> Just because we, as
> humans, are not able to measure, quantify, or qualify them very effectively
> by our standards does not mean that they are not an important defense
> system for a plant.

Well don't we prune and remove dead leaves and older stems etc?
Snails, shrimps and herbivores?
Older plant parts have algae, you cannot see it often unless bad, but you
can often "feel it". This Periphyton can be measured from these surfaces.

With fast growth in CO2 planted tanks, high light, good pruning, very little
periphyton will accumulate.

Less light, good CO2, etc will also produce very good results, and lower
periphyton biomass/chl a.
> I should note that it has been many years since I cracked a botany book so
> these are just my speculations. If others on this list feel the need to
> counter these ideas then so be it.
> --- Eric

The point of attachment, the leaf or stem is often covered by a waxy layer
called a cuticle. Most true aquatic plants have a very reduced cuticle, eg
Myriophyllum, some plants like Lobelia cardinalis/Aubias etc will have a
thicker cuticle. Amphibious plants will have a more developed cuticle

Sickly/stunted/half dead plants will grow slower and have more time to
accumulate this periphyton algal layer on their leaves. Less light is yet
another way to reduce the build up on slower growers. The build up of
periphyon is going to happen, adding less light but still good conditions
like CO2/nutrients will help, adding herbivore often will help.
Using a few fast growing stem plants that don't accumulate much will help.

Even a good shaking will remove about 80% of the algae off a a plant leaf.
I've seen the research paper, replanting and working that planted garden
will help.

Tom Barr