Stability of the Morphological Characteristics of the Semi-Aquatic Plant Phragmites altissimus Mabille (Poaceae) Alien to the Forest Zone of Eurasia

The discussion about the composition of the reed genus (Phragmites) and the nomenclature of individual reed taxa is still open. One of the most pressing questions is the taxonomic status of the highest reed (P. altissimus) due to its high invasive activity, recently noted in the forest zone of Eurasia. Many authors consider this species as a part of the closely related common reed (P. australis). This paper presents studies proving the species independence of P. altissimus based on comparative morphological analysis. We show that two closely related species, P. australis and P. altissimus, have statistically significant differences in morphometric parameters such as height of reproductive shoots, number of nodes on shoot, diameter of stem in the lower and upper parts of shoot, and length and width of middle leaves, as well as raw aboveground shoot biomass. We also found that P. altissimus stably retains morphological features in the forest zone of northern Eurasia and, according to the studied parameters, does not differ from P. altissimus from the region of the primary range of the species, except for the number of nodes on the reproductive shoot. This indicator is significantly higher in plants from the primary area compared to plants from the zone of invasion. The results confirm the species independence of P. altissimus, which retains its species-specific features within the entire modern species range.