stromata

Stomata, hold on—this article is about stromata, the plural of stroma. In biology, stromata is a term used across disciplines to denote a mass, layer, or framework of tissue that supports or encases other structures. The word stems from Greek stroma, meaning something spread out or a layer, and it is applied in several distinct contexts with little overlap between them.

In plant biology and physiology, stroma most commonly refers to the fluid matrix inside chloroplasts, which surrounds the thylakoid membranes. The chloroplast stroma contains enzymes of the Calvin cycle, chloroplast DNA, ribosomes, and various ions. When discussing multiple chloroplasts, some texts may use stromata, but stroma is generally treated as a non-count noun.

In histology, stroma denotes the supportive tissue of an organ, as opposed to its functional tissue or parenchyma. This stroma includes connective tissue and the extracellular matrix that provide structure and support for the organ’s functional cells. The term stromata may appear in some descriptions of multiple stromal tissues across organs, though the singular stroma is often used generically.

In mycology and plant pathology, stromata are compact masses of fungal tissue formed by hyphae on a plant host. These stromata can serve as a base for reproductive structures and may be crust-like, cushion-like, or darkened. They can be persistent and play a role in the identification of fungal species.

Stromata are distinct from stomata, the tiny pores on leaf surfaces that regulate gas exchange.