What is the primary characteristic that differentiates fungi from green plants?

Fungi are primarily distinguished from green plants by their lack of chlorophyll. This characteristic means that fungi do not have the ability to photosynthesize, a process that allows green plants to convert light energy into chemical energy using chlorophyll to capture sunlight. Instead, fungi obtain their nutrients through absorption from their environment, breaking down organic matter.

This fundamental difference in obtaining nutrients aligns with the distinct biological kingdom that fungi belong to, separate from the plant kingdom. While some might associate multi-cellularity with fungi, as many fungi are indeed multi-cellular, not all species fit this description, and some plants may also be multi-cellular. Additionally, reproduction methods, whether sexual or asexual, and nutrient absorption mechanisms do not serve as defining characteristics between the two groups when chlorophyll's presence is a clear and distinguishing factor.