Scientists group plants by a system called taxonomy. This system uses a hierarchical structure to classify plants based on their shared characteristics. Here's a breakdown of the key levels:

1. Domain: All living things are first divided into three domains: Bacteria, Archaea, and Eukarya. Plants belong to the Eukarya domain.

2. Kingdom: Within the Eukarya domain, plants belong to the Plantae kingdom.

3. Phylum (or Division): Plants are further divided into several phyla (or divisions), which reflect major evolutionary differences. Some of the major phyla include:

* Bryophyta: Mosses, liverworts, and hornworts

* Pteridophyta: Ferns, horsetails, and whisk ferns

* Coniferophyta: Conifers like pines, firs, and spruces

* Magnoliophyta: Flowering plants (also known as angiosperms)

4. Class: Within each phylum, plants are grouped into classes based on shared characteristics. For example, the Magnoliophyta (flowering plants) are divided into two classes:

* Monocotyledoneae (Monocots): Plants with one seed leaf (cotyledon), like grasses, lilies, and palms

* Dicotyledoneae (Dicots): Plants with two seed leaves, like roses, beans, and oak trees

5. Order: Classes are further divided into orders based on shared traits. For example, within the class Magnoliopsida (dicots), the order Rosales includes plants like roses, apples, and raspberries.

6. Family: Orders are divided into families based on more specific characteristics. The family Rosaceae, for example, includes roses, apples, pears, and strawberries.

7. Genus: Families are divided into genera, which group closely related species together. For example, the genus *Rosa* contains all species of roses.

8. Species: The lowest level of classification, a species is a group of organisms that can interbreed and produce fertile offspring. For example, *Rosa rugosa* is the species name for the rugosa rose.

This hierarchical structure helps scientists to understand the relationships between different plant groups, track their evolution, and identify new species.