Via Kottke.org, we are directed to Plants Can Tell Who's Who at naturenews.com.

plants grown alongside unrelated neighbours are more competitive than those growing with their siblings — ploughing more energy into growing roots when their neighbours don't share their genetic stock.

Plants 'know' more about their environment than they are often given credit for: they can sense the presence of neighbouring plants through changes in water or nutrients available to them or through chemical cues in the soil, and can adjust their own growth accordingly. "That plants have a secret social life is something well known to plant ecologists," says Dudley.

But the ability to recognize kin has not been demonstrated before.

For remainder of article, click here.

I suspect that just as we humans are hard-wired to both compete and cooperate (see Unhappy Lawyers and the Cooperative Hard-Wire) so are plants.  Because I don't know that, I ask any botanists within shouting distance to weigh in.

Collaborate, compete, protect, defend, balance, compete, collaborate. 

Ecclesiastes 3:1-8