intercalary

adjective

• 1(of a day or a month) inserted in the calendar to harmonize it with the solar year, e.g., February 29 in leap years.
• of the nature of an insertion:elaborate intercalary notes and footnotes

• 2 Botany (of the meristem of a plant) located between its daughter cells, especially (in a grass) at or near the base of a leaf.