What is folic acid? Why is the anemia caused by deficiency of folic acid known as megaloblastic anemia?

The folic acid (when ionized it is known as folate) is a coenzyme that participates in the synthesis and duplication of DNA and for this reason it is fundamental for cell division. If there is not enough folic acid in cells with great turnover, such as red blood cells, they have their production decreased.

In folic acid deficiency precursor cells (reticulocytes) that would originate erythrocytes (red blood cells) start cell division but the process is very slow while the cytoplasm growth is normal. So the cells became abnormally large, a typical feature of this part of anemia known as megaloblastic anemia.