Algae?

I have what I presumed at first was hair algae in my tank but having done
some reading up it doesn't appear to fit the description. It is a dark
blueish green colour and appears more structured than one would expect algae
to be - seems to have a central stem with branches coming off, looks a bit
like a minature silver birch in winter. It is growing on the leaves of my
crytpcoryne and also on the drift wood. Seems quite tough and well attached.
Any ideas on what it is and how to control it?

Thanks

--
Alan