The division of plants with the simplest organisms is Bryophyta, commonly known as mosses.

Here's why:

* Lack of vascular tissue: Bryophytes lack the specialized tissues (xylem and phloem) that transport water and nutrients in more complex plants. This limits their size and restricts them to moist environments.

* Simple reproductive structures: Bryophytes reproduce using spores, which are single-celled and lack the complexity of seeds found in vascular plants.

* No true roots, stems, or leaves: They have structures that resemble these features, but they are simpler and less specialized.

While some algae might appear simpler due to their single-celled nature, they are not classified as plants. Bryophytes represent the earliest and most primitive lineage of land plants.