<p>Coleus scutellarioides (L.) Benth. is a very popular ornamental plant with attractive colorful foliage and also has several medicinal properties. A detailed cytogenetical study was conducted in the ‘Red Trailing Queen’ horticultural form of this species. Hitherto, elaborate cytogenetic studies in this species received less attention and all of the previous studies on chromosomes are decades old. Thus, a reassessment and detailed cytogenetic study of this species are necessary. The karyotype study revealed that somatic cells contain 2n=48 small chromosomes, classified into metacentric to submetacentric. Meiotic chromosomes stained with acetocarmine and 4′,6-diamidino-2-phenylindole (DAPI) revealed the occurrence of univalent, bivalent, and multivalent associations of chromosomes along with secondary associations. The result confirms the allopolyploid origin of this plant. Meiotic irregularities like laggard chromosomes and multipolarity movement have also been found. In addition to that, variation in the chromosome numbers within pollen mother cells (PMCs) has been observed frequently. Pollen viability has been determined by fluorescein diacetate (FDA) and found to be very low. Rosmarinic acid (RA) is a natural polyphenol utilized as an anti-microbial, immunomodulatory, anti-diabetic, anti-allergic, anti-inflammatory, hepato-protectant, and renal-protectant agent. The RA content has been quantified through high-performance liquid chromatography (HPLC) to find out the medicinal efficacy. The present investigation on detailed cytogenetics study along with the pollen viability will be beneficial in the breeding program and accordingly useful in further improvement of this ornamental medicinal plant.</p>