Dear Lady Iris!

Iris Cohen wrote:
ts already too big to be Mimosa pudica and the bipinnate foliage is too
large.

I agree. Sir,

Umm, I'm not sure, if I am a Sir

where did you get your Euphorbia?

The daughter of my girlfriend brougt it home. I'll ask her. Ok,
it is from a "Holland Blumenmarkt" (a brand name for a plant
supermarket, literally "Holland Flowermarket").

That may give us a clue as which acacia you have.

I'm fine with knowing it's an acacia. But we can explore this
further if you like.

It looks like some kind of Acacia. Give it more light to get less stringy
growth. You won't be able to tell the species until it blooms. Look up Acacia
to see if it matches.

That was nice, suggesting more light rather than calling it a
weed. If we keep the plants together, would the acacia kill the
euphorbia? Since we won't probably move the pot to a brighter
spot, we thought of separating the plants. The acacia roots have
come long out of the inner pot hole and are now in the water in
the outer pot. We'd probably have to break the inner pot and drop
the soil of both plants roots to separate them. Does that sound
risky?

Does it have any thorns?

Actually, yes. There are some at some forks. They are soft yet.
On top of some forks there are nectar drops. One had a honey like
consistency and another one dried out.
On http://bksys.at/bernhard/img/x14/-gallery.html there are closeups.

Thanks everyone for your help.

Bernhard