Final answer:
Botany is the branch of plant science that focuses on the classification and taxonomy of plants and related organisms.
Step-by-step explanation:
The branch of plant science responsible for developing methods for grouping organisms is Botany. Botanists study organisms such as plants, algae, some bacteria, and organisms that have plant-like features, such as fungi. Classification and taxonomy are integral parts of botany, where plants are organized and grouped based on their characteristics.