What's the plural form of big sagebrush? Here's the word you're looking for.
Answer
The noun big sagebrush can be countable or uncountable.
In more general, commonly used, contexts, the plural form will also be big sagebrush.
However, in more specific contexts, the plural form can also be big sagebrushes e.g. in reference to various types of big sagebrushes
or a collection of big sagebrushes.