Plants have primitive eyes, how much can they see?
In the wake of ecologist Suzanne Simard's TED talk about her research showing that trees communicate via chemical signals and recognize their own offspring and Peter Wohlleben's book “The Hidden Life of Trees", we probably shouldn't be too surprised to learn that plants may be watching as well.
The modern thread of this story starts with cyanobacteria - single-celled blue-green algae. These tiny plants move towards and away from sources of light, but new research finds that this is more than just reactivity to a physical trigger. It turns out the entire cyanobacteria acts like a tiny eye, the naturally round cell membrane permits the entry of light on one side and the organism can distend itself to focus that light on receptors on the opposite wall, a somewhat foggier version of the way our eyeballs allow us to perceive details in the world around us.
The tale goes back to the days of Francis Darwin, son of the famous evolutionary theorist Charles, who hypothesized in 1907 that leaves have "eyes" that combine a lens-like apparatus with light-sensitive cells. These structures, called "ocelli" from the Latin for little eyes, were confirmed to exist but further interest in what exactly plants can do with them lagged until recently.
As scientists have learned more about the biochemistry of vision, they realized that some plants make proteins associated with eyespots, a feature of the simple visual apparatus used in single-celled organisms. Cabbage is one of these - giving our use of the term "head of cabbage" new depth.
Some have even gone so far as to suggest that the vine Boquila trifoliolata "sees" details of shapes in its environment. This South American vine displays an amazing ability to change its appearance to match various plants around which it twines itself, sometimes even growing differently shaped leaves in two places along the same vine. (Other mechanisms, including chemical communication or some sort of genetic transfer, have also been proposed.)
At any rate, there is more to our planet's foliage than meets the eye.