Nick Lane considers eyes to be one of the ten great inventions of evolution.

an excerpt from Life Ascending by Nick Lane (2009)

Sight is quite a rarity. Eyes are absent, at least in a conventional sense, from the plant kingdom, as well as from the fungi, algae and bacteria. Even in the animal kingdom eyes are not at all common property. There are said to be thirty-eight fundamentally different models of body plan - phyla - in the animal kingdom, yet only six of them ever invented true eyes. The rest have endured for hundreds of millions of years without the benefit of seeing anything at all. Natural selection did not scourge them for lacking sight.

Set against this spartan background, the evolutionary benefits of eyes loom large. ... we find that 95 percent of all animal species have eyes; the handful of phyla that did invent eyes utterly domi- nates animal life today.

Well, Lane’s objectivity might be overshadowed by his belief that evolution’s "inventions" introduce some value hierarchy in living species. Hierarchy is an invention of human mind, a troublesome one. Why he says that " the rest have endured for hundreds of millions of years without the benefit of seeing"? Endured? Plants are not suffering for hundreds of millions of years, they are living for hundreds of millions of years . If plants don’t need eyes, why they should "invent" them? Besides, on what grounds one can claim that plants don’t have the faculty of seeing?

Terrence W. Deacon presents another approach:

an excerpt from Incomplete Nature by Terrence W. Deacon (2012)

Through recent years have seen a shift in emphasis back toward the molecular mechanisms of cell differentiation and structural develop- ment, the term morphodynamics is still used in approaches that focus instead on geometric properties involved in the formation of regular cellular structures, tissue formation, and body plan. A classic example is the regular spiral whorls of plant structures, called spiral phylotaxis, where shoots, petals, and seeds often grow in patterns that closely adhere to the famous Fibonacci number series (1, 1, 2, 3, 5, 8, 13, 21, 34, 55, ...), which is generated by adding the two previous numbers of the series to produce the next. Plant structures like leaves and branches that follow Fibonacci spirals are arranged so that they are maximally out of each other’s way for nutrient delivery, for exposure to the sun, and so forth.

Mathematical models of this process have long demonstrated that this pattern reflects growth processes in which unit structures are added from the center out in a way that depends on how previous units have been added. ... This indicates that the Fibonacci growth pattern is not dependent on any intrinsic templates or archetypal form (e.g., encoded directly in the genome). It is induced to emerge

by the interactions of diffusion effects, the geometry of growth, and the threshold level of this signal at which point new plant tissue will begin to be generated.

I’ve inserted the above quote because of another approach, not because it answers the question of plant sight. Deacon’s approach is burdened with heavy formalism. (On the side, the models he is talking about are biological models, not models of in mathematics; the usage of a mathematical object in a model, like number series, does not make that model "mathematical".) However, Deacon puts forward an important notion that the geometry of plant growth is a result of the interactions with environment. Then, the question remains: how a plant can "see" and recognize (!) an environment object without a direct body contact?