It's a type of kelp. I had it in my tank for years and years. It's beautiful and perfectly fine to have but doesn't always grow well for everybody. It's one of the more temper-mental plants I've had and was VERY slow growing for me. It was crazy hard to transfer without chopping off some of the rock to transfer the holdfast which didn't make sense to me. Does your friend have a secret for growing it so well? If so I want to know it!