Tanacetum tenuissimum is reported as a new record from E Azerbaijan province (NW of Iran). The species by having some characters such as plant height (15–40 cm), length of pappus (0.2–0.4 mm), achene length (1.8–3.2 mm) and ribs (6–10), margin of pappus (crenulate), length and width of capitula (4.5 × 8 mm), and basal leaves (5 × 1 cm) are distinguishable from its close relative T. tabrisianum. In addition, the survey of light and scanning electron microscopy showed pollen grains are tricolporate and echinate (Anthemis-type). Based on the P/E ratio (Polar axis/Equatorial diameter), shape and percentage of the pollen grains were found to be oblate-spheroidal (75%), suboblate (15%), and spheroidal (10%). Distribution map of the new record species and two relatives (T. canescens and T. tabrisianum) in the world and Iran, morphological and micromorphological characteristics of pollen grains and identification key are presented herewith.
