Background Castor (Ricinus communis L.) seeds contain a large amount of oil that has several biological activities. In the current research, phytogeographic distribution, seed morphological characteristics, molecular genetic diversity and structure, and fatty acid composition were investigated in nine Iranian castor populations. Methods and results The cetyltrimethylammonium bromide (CTAB) protocol was used to extract the nuclear genomes. These were later amplified using 13 SCoT molecular primers. The phytogeographic distribution was determined based onthe Zohary mapping, GC apparatus determined the fatty acid composition of the seeds. GenAlex, STRU CTU RE, Geno-Dive, PopGene, and PopART software were used for the statistical analyzes. On phytogeographic mapping, the harvestedpopulations belonged to different districts of the Euro-Siberian and Irano-Turanian regions (Holarctic kingdom). Most ofthe quantitative morphological traits of the seeds differed significantly (P ≤ 0.05) between the populations. The AMOVAtest demonstrated a large proportion of significant genetic diversity assigned among populations, which were approved by some estimated parameters of genetic diversity such as Nm, Ht, Hs, and Gst. Nei’s genetic distance and structure analysis confirmed the existence of two main genotype groups and some intermediates. However, there was no isolation by distance between the genotypes. Unsaturated fatty acids were detected as the main component of seed oil with linoleic and ricinoleic acids. Significant correlations were detected between the main fatty acids of seed oil with seed morphological traits, geographic distance and the geographic parameters of habitats. According to the composition of the seed fatty acids, four chemotypes groups were detected.Conclusions The classification patterns of the populations based on molecular genetic data, fatty acid composition, andphytogeographic mapping were not identical. These findings indicated that Iranian castor populations had unusual seed fatty acid composition which strongly depended on habitat geographic factors and seed morphological traits. However, theidentified chemotypes and genotypes can be used in future breeding programs.
