Abstract
The Black Irtysh River, a major tributary of the Ob River, traverses diverse ecological zones, influencing the distribution and composition of its floodplain vegetation. This study focused on the Black Irtysh River valley, a key segment of the Irtysh basin, to assess the current state of its plant communities. To compile expedition routes and a preliminary floristic list, a critical revision of more than 1000 herbarium sheets was carried out in the herbarium collections of Kazakhstan (Altai Botanical Garden and Institute of Botany and Phytointroduction). During the field season, a study of plant biodiversity was carried out along the entire coastline of the Black Irtysh. As a result, 217 species of higher vascular plants were identified (55% of those previously found in herbarium archives) from 139 genera and 43 families. The habitats of two Red Book species were discovered: Tulipa patens and Tulipa uniflora. It was found that the flora of the Black Irtysh is similar to the flora of the entire Zaisan depression, and families Poaceae, Asteraceae, Amaranthaceae, Caryophyllaceae, Rosaceae, and Fabaceae are predominant. Geobotanical surveys revealed that the species composition of plant communities is poor and similar among survey points. Only the western part of the river delta is characterized by high rates of projective cover and reserves of forage plants. The main factors of anthropogenic influence are fires, livestock grazing, and deforestation.