They can also recognize their siblings.[1]

[1] http://www.nature.com/news/2007/070611/full/news070611-4.htm...

I read it first here [1] back in July. I think it was posted here as well.

[1] http://munews.missouri.edu/news-releases/2014/0701-plants-re...

Url changed from http://modernfarmer.com/2014/10/plants-can-tell-theyre-eaten..., which points to this.

Please don't anthropomorphize plants...they really hate that.