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Non-aroid query: Ruellia amoena

I hope you will forgive this breach of aroidal relevance (made worse by my
being one of the listowners!); I spent some time trying to decide where to
post this, concluding it didn't fit on any list to which I belong. But I
know there are many people on Aroid-L who grow many things beside aroids,
and who have incredibly wide-ranging knowledge, and I know several of them
grow this plant. 

Seven or eight years ago, Phil Mueller sent me a piece of a ruellia which
he said "grew all over the place" in New Orleans to see the bright red
flowers. I rooted the piece and have been enjoying it ever since. I
tentatively identified it as R. amoena (for a close-up of a flower, see:


or of the entire plant:



Though not hardy here, and a bit sprawly, and of course being a ruellia it
shoots seeds everywhere, I like it - it's in full flower now, and it's a
real bright spot in the greenhouse. 

But one mystery I haven't solved: what is that stuff that forms all over
the leaves when it's inside for the winter? And why does it form? And does
it do that for anyone else who grows it? It's a white substance, maybe
very very slightly sticky but mostly just feels gritty, forms on both
surfaces of the leaves, doesn't seem to be there when the plant is outside
in summer (or maybe it's just washed away by the sprinkler), doesn't seem
to be contagious, and doesn't seem to do the plant a bit of harm. 

It wasn't apparent when the lopped-off piece arrived, but appeared within
a month or two. When I bring the plant(s) in in the fall, it's not present
but appears within a couple of months at most.

Although it didn't look like any of the usual insect pests to me -
mealybugs, scale, spider mites (and being nearsighted, spider mites are
usually perfectly visible to me), etc. - my initial assumption was
"something bad". But as I say, there seems to be no harm to the plant - no
loss of vigor, or color - and it doesn't spread to anything nearby.

Today, having some time, I started with a magnifying glass, working past
20x hand lens up to a cheap microscope. Best results seem to be at
50-100x, where it appears to be almost crystalline in nature. It has no
detectable smell or taste to me, although one of my cats seems interested
in it (but doesn't eat the plant). It certainly doesn't look insect-like
in any way.

Does anyone have any ideas?



-- Steve Marak
-- samarak@arachne.uark.edu

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