Here's why:

* Complex Structure: Cattails are plants, and plants are composed of many different types of cells that work together to form tissues and organs.

* Specialized Cells: Cattails have specialized cells for functions like photosynthesis, water transport, and reproduction.

* Visible Structure: You can clearly see the different parts of a cattail, like the leaves, stem, and flower spike, indicating a complex multicellular structure.

Unicellular organisms, like bacteria or amoeba, are made up of only one cell. Cattails are much more complex!