This picture of Acropora austera is a clone of the one above. They have been grown in two different tanks under the same lighting but with very different flow conditions. This one doesn't receive much flow so the branches are thin and the growth is upright. The other coral receives extremely high flow and has grown thick and horizontal. They almost look like two different corals. This is a prime example of why it is so difficult to identify them.
Regards,
Kevin