Eustigmatophyceae

Eustigmatophyceae is a class of photosynthetic algae within the phylum Ochrophyta, part of the larger group of stramenopile (heterokont) algae. Members are primarily unicellular to very small colonial forms that inhabit marine and freshwater environments around the world. They are important components of phytoplankton in many ecosystems and contribute to primary production.

Morphology and physiology are relatively uniform across the group. Cells are typically small and oval or spherical, with a simple to moderately complex plastid. Pigment composition is characteristic of ochrophyte algae, including fucoxanthin, which gives a brownish hue to many species. Eustigmatophyceae store energy mainly as lipids in cytoplasmic droplets, and some species can accumulate large lipid reserves under particular environmental conditions. The cell walls are generally thin and uncomplicated compared with some other algae.

Reproduction is predominantly asexual, occurring by mitotic division. Sexual reproduction has been reported in a few species but is not well understood and is considered rare or rarely observed in natural populations.

Ecologically, Eustigmatophyceae play a role in aquatic food webs as primary producers and as a source of organic matter for various microorganisms. Several genera have been investigated for biotechnological potential due to their lipid productivity. The best-known and economically significant member is the genus Nannochloropsis, widely studied for its lipid content, particularly for production of polyunsaturated fatty acids and its use in aquaculture feeds and biofuel research.

Taxonomically, Eustigmatophyceae are placed within the ochrophyte lineage of the Stramenopiles. The class comprises multiple genera distributed across aquatic habitats, and taxonomic refinement continues as molecular methods clarify relationships within the group.