Please ID this for me

[ibefishy]

I saw this growing in my tank for the last few weeks and finally figured I would get around to finding out what it is. Anyone? It has an almost leather-like appearance but is soft to the touch. Is it something I should be concerned about?
Any info or ideas would be great.

Thanks

[zhenya]

I'm tempted to say that it is a brown algae Padina sp., or it could be an encrusting brown leaf algae Lobophora variegata.
Do some Google searches using those keywords and I'm sure you'll get some hits.

PS. Here's a photo of Padina algae, but there are tons more online.
A photo of Padina gymnospora algae - A photo of Padina gymnospora algae