Macromorphological-micromorphological achene characteristics of genus Persicaria from temperate Himalayas were studied using scanning electron microscopy, stereomicroscopy, and light microscopy to investigate their correct identification, taxonomic implications and classification. The achene ultrastructure of Persicaria exhibits significant variations, with a diverse array of micromorphological characteristics observed. Achene micromorphological attributes were studied by different microscopic techniques, including achene size, color, shape, outline, texture, sculpturing, and periclinal and anticlinal wall patterns. Achene shapes were classified into different categories as trigonous, circular-biconvex, trigonous-biconvex, trigonous-bigonous, elliptic, biconvex, biconvex-trigonous, broadly ovate, and ovate-trigonous. Achene colors were black, black-dark brown, dark brownish, light brown-dark brownish, and black brown. SEM-based micromorphology features include achene sculpturing as finely vereucate, striate, psilate, reticulate to papillate, rugose, reticulate to granulate, striate to regulate, puncticulate, and striate to puncticulate. The range of achene length varied from 1.62–4.35 mm, maximum length was observed in P. amplexicaulis (3.51–4.35=4.02±0.18) mm, and minimum was in P. sinuata (1.62–1.99=1.86±0.08) mm. Epidermal walls included slightly regular to regular arrangements. A taxonomic key was created using micro- and macro-morphological characteristics to aid in distinguishing species boundaries and facilitating efficient identification within the Persicaria genus. The achene morphology of Persicaria along an altitudinal gradient of 1300–2700 m was described with precise diagnostic importance of characters using SEM. P. sinuata was recorded from a narrow altitudinal range of 2400–2700 m with a restricted habitat within the upper temperate zone. This research work seeks to determine the taxonomic implications of achene morphology for the first time in the selected Persicaria species from the temperate Himalayas.