bicellular

Bicellular is an adjective meaning composed of two cells or containing two cells. In biology and botany, the term is most often applied to pollen grains that have two cells at the time of their release: a large vegetative (tube) cell and a smaller generative cell.

In many angiosperms, pollen is bicellular when it is shed from the anther. After pollination, the generative cell divides by mitosis to form two sperm cells within the pollen grain as the pollen tube grows toward the ovule. This developmental pattern contrasts with tricellular pollen, in which three cells (one vegetative cell and two sperm cells) are already present inside the grain at anthesis.

The distinction arises during microsporogenesis and subsequent pollen development. A microspore typically gives rise to a vegetative cell and a generative cell; in bicellular pollen, the second mitotic division to produce two sperm cells occurs after pollen release or after germination on the stigma. In tricellular pollen, the two sperm cells are formed before pollen is shed.

Distribution and variation occur across plant groups. Bicellular pollen is common in many monocots, including most grasses, and is also found in various dicot lineages. Some dicots exhibit tricellular pollen, where the sperm cells develop prior to pollination.

Etymology: bicellular derives from bi- meaning two and cellular meaning relating to cells. In practical terms, the term helps describe differences in male gametophyte development and fertilization mechanisms among flowering plants.