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Re: Why no variegation?

Yesterday, Glen & Mo Lee asked:
> I have four Filipendula ulmaria 'Variegata' plants growing
> throughout my garden.  Three of them are beautifully variegated.
> They look as though someone spilt a can of yellow paint on
> their dark green leaves. I'd estimate 80% of the leaves are
> variegated in this manner on these 3 plants.  The fourth plant
> has very little variegation on it, maybe 10% of its leaves
> are variegated. 

> My question is this:  will this one plant with little variegation
> continue to be so in future years?  Or, is it possible that next
> year this one plant will be the only one with heavy variegation
> and my other three plants may have very little variegation?
> 
> I'm attempting to start several more of these plants from cuttings.
> If successful I was thinking of replacing this poorly variegated
> plant with one of the cuttings, but I began to wonder if maybe 
> this plant could look heavily variegated next year.

Variegated plants are frequently chimeras.  What's a chimera?  Re-read
Greek mythology.  Chimeras were monsters that were part man, part beast. 
A centaur would be a chimera, as would a griffin.  

In plants, chimeras are tissue combinations of different genetic
backgrounds.  For a green:white color variegation, there are cells with
normal green chloroplasts, and cells that are not green, because something
has gone wrong in the production of the chloroplasts.  

The mutations that create chimeral plants rarely include the
germ cells (the cells that produce sperm / pollen or egg / seed).  These
mutations are usually in the surface layer, although sometimes are deeper
into the plant tissue.  If the mutation is in the surface layer, and not in
the germ cells, then the germ cells remain unmutated (in this case, green).
 Green germ cells will produce green plants.  

The same phenomenon occurs with taking cuttings from variegated plants. 
Stem cuttings will frequently send up green sprouts.  Leaf cuttings will
usually send up green shoots.  And it's all for the same reasons.  If the
variegation mutation is in the surface layer, the shoots (which generally
result from a deeper tissue layer) will emerge green.  If the mutation is
in a deeper layer, the shoots may emerge variegated.  If the mutation is in
the germ cells, the seeds (assuming self-pollination) will produce
variegated plants.

There is a chimera in the botanical literature that occurred when a Solanum
species was grafted onto a tomato (Lycopersicon) plant.  One sprout from
the graft union apparently had the surface layer of the Solanum, but the
inner layers were tomato.  What was interesting was that the Solanum was
insect-resistant (as many of them are, thanks to the glandular hairs) and
so was the chimera.  

Glen and Mo, what seems to have happened is that the chimeral mutation is
indeed in the surface layer.  My best guess is that the perenniating buds
that produce the next year's plants include a portion of the surface layer,
but the bud itself comes from a deeper layer of tissue.  Surface layer
chimeras frequently are not continuous around the entire surface layer of
the plant.  Some sections of the surface are variegated; others are green. 
These are called sectoral chimeras, and that's what seems to be happening
with your Filipendula.  Sectoral chimeras are not terribly stable, and
every propagation will risk a reversion to green, depending on where in the
crown the bud originated (variegated sector vs green sector).  

All you can do is to watch what happens and rogue out the plants that lose
their variegation.  My suspicion is that every year, a small percentage
will emerge green or with altered variegation, but that most will be the
way you like them.  

Rick Grazzini
rickg@centrelab.com
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