what has a sticky surface where pollen lands

the function of the pollen sac is to produce pollen (pollen grains). The pollen sac is the microsporangium of a seed plant in which pollen is produced. Most plants except coniferous plants contain four (4) pollen sacs.

microsporangium

pollen grains are produced in pollen sac of anthers which are present on the male gamets of flower

Matured pollen grains contained sperm cells. When Pollen grains are sticky, you have pollen. Pollen grains are contained in the pollen sac, with the purpose of helping plants reproduce.