Abstract
Summary: Many lower land plants have cells that contain a single plastid. A monoplastidic condition is observed in dividing vegetative cells of hornworts, the moss Takakia, and some microphyllophytes(Isoetes and Selaginella). Sporogenous cells and sporocytes are monoplastidic in all mosses, hornworts, Isoetes and Selaginella, as well as some species of liverworts, Lycopodium and Angiopteris. Additionally, spermatocytes in the taxa mentioned above are typically monoplastidic. In monoplastidic cells, the single plastid divides before nuclear division and divided plastids seem to serve as microtubule organizing centers of mitotic apparatus. Such a monoplastidic condition is considered to be a critical symplesiomorphy among bryophytes, lycopsid pteridophytes, and the coleochaetalean algae. In this paper, we summarize the results of recent investigations on monoplastidic cells of lower land plants.