Contribution to the taxonomy of the genus Amaranthus: seed observations and characterization of seed oil

Amaranths, particularly grain Amaranthus, are a substitute for high-nutritional-value crops and are considered the golden crop of the future. The studies of the genus Amaranthus that have been recently published indicate that this underused crop has not received the attention it deserves. Taxonomic delimitation in the genus Amaranthus has become much more challenging due to a high number of morphotypes, synonyms, germplasm, overlapping morphological traits, and frequent misapplication of names. Hence, the field of Amaranthus research is vast, but many taxonomic issues need to be resolved. Most focus was on cultivated Amaranthus, whereas no attention was paid to wild species. A comprehensive research strategy is required to project Amaranthus as a future golden crop. Thus, the main objectives of the thesis, related to basic and applied research, were the next: (1) to investigate the occurrence and invasion status of Amaranthus hypochondriacus in Belarus, Estonia, Italy, the Netherlands, and the North Caucasus to understand its distribution in relation to the bioclimate. (ii) to investigate the taxonomic value of the seed's micromorphological features using the Scanning Electron Microscope (SEM) in order to improve the understanding of the taxonomy of the genus Amaranthus at the global scale. (iii) to study oil and squalene content from the seeds of different Italian Amaranthus species to contribute to the selection of wild species more effective in producing these compounds. Three kinds of studies were carried out to accomplish the objectives. In study I, we discussed our observations on A. hypochondriacus L. in relation to its distribution and invasion status in Belarus, Estonia, Italy, the Netherlands, and the North Caucasus. For Italy, we modified the status from casual to naturalized based on living individuals who had sustained themselves for 5 to 20 years. Regarding the other countries, we confirmed the species' invasion status (which had been inconsistently described in the literature), indicating it is a casual alien in Belarus, Estonia, and the North Caucasus and naturalized in the Netherlands. In research II, we investigated the nomenclature and taxonomy of the genus Amaranthus and presented a comprehensive study on Amaranthus seed micromorphology. The species was identified using a stereomicroscope, the LEICA EZ4W. A scanning electron microscope (JSM5910, 3kv voltage, and secondary electron detector) was used to analyze the micromorphological seed characteristics. The results show that seed micromorphology can be a helpful tool in Amaranthus taxonomy. Still, various species cannot be differentiated using these features (for example, the so‐called “deflexus‐type,” comprising A. vulgatissimus, A. cacciatoi, A. spinosus, A. dubius, and A. stadleyanus). These findings confirm the taxonomic complexity of the genus Amaranthus once again. In experiment three, the chemical characteristics of seed oil, specifically squalene, free fatty acid, tocopherol, and sterol, were extracted from six Amaranthus species, collected in situ, and analyzed using the Accelerated Solvent Extraction (ASE) apparatus. This study provides data on the squalene, free fatty acid, tocopherol, and sterol content in the oil of six Amaranthus species found in natural habitats for the first time. The smallest seeds (A. tuberculatus) have the highest percentages of oil and squalene, while the largest seeds (A. muricatus) have the lowest percentages. There is also evidence that specimens from lower altitudes had the highest concentration of fatty acids. According to our findings, the six wild Amaranthus species demonstrated features comparable to commercial species, exhibiting medium-high oil and squalene content. This study reveals that the collection site influences the oil and squalene content of the Amaranthus species.