[4] If a trophic mode is obligate, it is always necessary to sustain growth and maintenance; if facultative, it can be used as a supplemental source.
However, this characterisation as mixotrophic could be extended to a higher number of clades as research demonstrates that organic forms of nitrogen and phosphorus—such as DNA, proteins, amino-acids or carbohydrates—are also part of the nutrient supplies of a number of plant species.
Consider the example of a marine protist with heterotrophic and photosynthetic capabilities: In the breakdown put forward by Jones,[19] there are four mixotrophic groups based on relative roles of phagotrophy and phototrophy.
An alternative scheme by Stoeker[18] also takes into account the role of nutrients and growth factors, and includes mixotrophs that have a photosynthetic symbiont or who retain chloroplasts from their prey.
Another scheme, proposed by Mitra et al., specifically classifies marine planktonic mixotrophs so that mixotrophy can be included in ecosystem modeling.