The phrase "a complex mixture of species" is correct and usable in written English.
It can be used in contexts discussing biodiversity, ecology, or chemistry, where different species or elements are combined in a complicated way.
Example: "The rainforest is home to a complex mixture of species, each playing a vital role in the ecosystem."
Alternatives: "a diverse array of species" or "a varied combination of species".
Fifty years ago, biochemists described cells as small vessels that contain a complex mixture of chemical species undergoing reactions through diffusion and random collision.
Invasive stands of mesquite in South Africa comprise a complex mixture of several species and their hybrids (Mazibuko 2012), and we will simply refer to as "mesquite".
Dietary lipids constitute a complex mixture of lipid species, some of which are highly water insoluble in nature.
Ambient PM samples contain a complex mixture of chemical species that may produce HOOH in a more complicated mechanism than in the pure laboratory solutions measured here.
Pyrolysis is used to convert lignocellulosic biomass into a complex mixture of phenolic-rich species that can be used in a transportation fuel.
These results unambiguously confirmed that the copurified αGC661βGC protein is a complex mixture of different oligomeric species.
The exposure of biological membranes to reactive oxygen species creates a complex mixture of distinct oxidized phospholipid (OxPL) species.
Exposure of biological membranes to reactive oxygen species creates a complex mixture of distinct oxidized phospholipid (OxPL) species, which contribute to the development of chronic inflammatory diseases and metabolic disorders.
The forests in the Adirondacks Region of New York are a complex mixture of hardwood and softwood species that have a long and varied history of natural disturbance occurrences (Lorimer and White 2003) and human management (McMartin 1994).
PICs released from solid fuel combustion are a complex mixture of particulate and gaseous species.
