suberin

Suberin is a specialized biopolymer that provides a hydrophobic seal in plant tissues. It is primarily associated with the formation of cork and the Casparian strip in roots, where it serves as a critical chemical barrier to regulate the movement of water and dissolved minerals.

As a chemical substance and a biological material, it is treated as an uncountable noun. It does not have a plural form in standard botanical or chemical discourse, as it refers to the material itself rather than individual units.