Because of the limitations of spell selection, elemental concepts work best if choosing any two elements out of the four.
Currently I am treating damage types as paraelemental.
lightning-thunder (Air, Water)
radiant-fire (Air, Fire)
acid (Fire, Earth)
cold-bludgeon-pierce-slash (Earth, Water)
So the Fire elementalist accesses radiant, fire, and acid.
Additional elements:
psychic-force (Ether the quintessence)
poison-necrotic (Plant)
Ether is the proto element of the Big Bang and includes conscious soul and fundamental forces like gravity. Ether is both immaterial yet physical. The four elements of matter are made out of ethereal fundamental forces.
Plant is a kind of living element, that emerges from the entangling of the five elements. The Plant element also includes the fabrication of complex objects, that weave together metal, cotton, leather, etcetera, and spells like Mend. Fungus as an aspect of Plant especially corresponds necrotic damage.
Void
Void is the nothingness of the vacuum of empty outer space. It relates to teleportation across spacetime, remote presence, and prescience.
So far, there are seven elements:
Four states of matter (Earth, Water, Air, Fire)
Immaterial physical protomatter (Ether)
Living matter (Plant)
Space (Void)