Question

How a pollen grain recognizes the stigma of its own species for its germination?

Answer 1

Answer:

Air is fulled of plant species pollen grains, these pollen grains landing on stigmas, some germinate producing pollen tubes and then ceased to extent within stigma tissues, some other never germinate, other germinate and and of the same variety accomplished  fertilization. However, even of the same variety failed to fertilize the egg.

Answer 2

Well... It's not the pollen grain who recognises stigma its the other way around.

There is a continuous dialogue between pollen grain and the pistil , mediated by chemical components of the pollen interacting with those of the pistil which results in the acceptance or rejection of the pollen grain.