Ephedra is a genus of jointed, almost leafless shrubs of dry Asian uplands, green-stemmed and broom-like, and it has two quite separate histories.
In Chinese medicine it is ma huang, in continuous use for around two thousand years, prescribed for cold, wheezing and fever and named in the classical materia medica. Its action is stimulant and bronchodilating, and it is one of the few traditional plants whose active principle, ephedrine, became a standard pharmaceutical in its own right.
Its religious role is Zoroastrian. Ephedra is used as hom in the modern Parsi and Irani Yasna, the central Zoroastrian ritual, in which the plant is pounded in a mortar with water and pomegranate twigs and the juice is consecrated and drunk. This is a living ceremony with an unbroken liturgical tradition, and the plant used in it is ephedra.
That is the strongest argument for ephedra as the historical haoma: not what it does, but that the ritual never stopped. Ephedra twigs have also been recovered from ritual contexts at Bronze Age sites in Central Asia, in association with vessels, which supports antiquity independently of the liturgy.
The plant is included in this atlas primarily as a candidate rather than as an entheogen, because its own effects are not visionary and the atlas needs to be able to name the contenders in a dispute it does not resolve.