The Rigveda describes a mountain plant of stalks and shoots, never mentioning root, leaf, flower, seed or fruit, and never names it in identifying terms. The Brahmanas already prescribe substitutes, so the plant had passed out of reach inside the tradition itself. Fly agaric, ephedra and Syrian rue each have serious advocates and each faces an objection that has not been answered.
What would resolve this Residue analysis of pressing stones, strainers or storage vessels from a securely dated Indo-Iranian ritual context, with the identification independently replicated. Earlier claims of ephedra in Central Asian Bronze Age vessels have not settled the matter, so replication rather than a single result is what is needed.
OpenArchaeobotany and residue chemistry, working with Vedic and Avestan philologyR. Gordon Wasson, Soma: Divine Mushroom of Immortality