Of the many plants and fungi surveyed in the 'ahadith traditions of the Shi'a Imams is harmal, a botanical category unique for its seeds that, when prepared accordingly, produce a psychoactive effect. This paper presents evidence that suggests that the harmal referenced in canonical Shi'a sources is the same soma-haoma found in the respective Vedic and Zoroastrian traditions, thought to induce spiritual and oneiric inspiration and employed in religious ritual. Our inquiry begins and ends with 'ahadith contained in Baqir Majlisi’s Bihar al-Anwar, proceeding as a type of thought experiment, at each step presenting information that elucidates the harmal’s background (later featured as espand in numerous poems) and accretive development as a vegetal sacrament. The data that we cull from a diversity of sources, including religious doctrines, philological analyses, plant physiology research and archaeological remains, suggests that Muslim authors of the early Shi'a canon, in communication with preceding spiritual traditions, were aware of the mystical properties of this variety of “celestial botany.” From this evidence, we present the various attempts to name and distinguish the harmal’s plant variety, along with the enduring epistemic challenges that have historically frustrated this effort. We conclude, based on the methodological and philological fitness of their study, that Flattery & Schwartz’s (1989) botanical identification of the harmal as Peganum harmala is the current most creditable attempt at the plant’s disclosure. Although theories as to the harmal’s influence on the motifs of Islamic art and architecture in the Iranian Plateau are increasingly abundant, our study asserts that, however suggestive of ineffable spiritual experiences, these theories are still highly speculative. What does appear, rather, is a panoply of synergistic Indo-Iranian themes undergirding much of the religious ethos witnessed in the 'ahadith that must be considered further in approaching the latter’s authentication. Key words: Shi'ism, harmal, Iranian Plateau, soma-haoma, angels, entheogens, Bihar al-Anwar.