The outermost layer consisting of ground tissue in a stem is called the cortex.

Here's a breakdown:

* Ground tissue: This is the fundamental tissue system of plants, filling the spaces between the vascular tissue and epidermis. It's responsible for photosynthesis, storage, and support.

* Cortex: This is the outermost layer of ground tissue in a stem, located just beneath the epidermis.

* Epidermis: This is the outermost layer of cells, providing a protective barrier for the stem.

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