Context: Most aquatic macrophytes are ecozone-endemic species, and approximately two-thirds of them have rare occurrence at global scale. These small-range plants are seriously under-studied at macroecological scale, despite their marked vulnerability to extinction through habitat loss and climate change. Aims: To identify global hotspots of endemism and rarity of aquatic macrophytes and examine the factors that resulted in speciation hotspots of macrophytes in some areas of the planet. Methods: We analysed a database of 3499 macrophyte species to locate speciation hotspots and assess the biogeographic and environmental drivers that maintain ecozone-endemic, and globally rare species within their current limited global areas of occupancy. Key results: Ecozone-endemic and globally rare macrophyte species hotspots across the planet showed similar occurrence patterns and drivers among ecozones. Ecozone environmental conditions, particularly harsh environments, influenced macrophyte phylogenetic diversity and structure. Most macrophyte species diversification is recent (<10 million years ago). A negative association with bird-mediated zoochory was seen for endemicity and rarity hotspots. Conclusions: This study identified hotspots of endemicity and rarity, and potential cradle and museum speciation areas. Implications: Our findings could inform global action to conserve the macrophyte diversity of wetlands, and other inland aquatic habitats, across the world.

An ecobiomorphological profile of the water soldier Stratiotes aloides L. has been established based on materials obtained in the western Siberian part of the species range. This species has been found to be a perennial (vegetatively-oligenial) polycarpic rooted rosulate stolon-turion vegetatively-mobile surface-blossoming mesotrophic conditionally limnetic detritus-pelophilic hydatophyte.

An assessment of Hydrilla verticillata (Hydrocharitaceae) distribution was made, with the involvement of a wide range of data (herbarium collections, Web resources, literature sources, and authors' observations), covering the period 1811-2016. It is shown that Hydrilla is a plurizonal macrothermal semicosmopolite species with many disjunctions in the geographical range. In the 20th century, H. verticillata expanded its secondary range significantly, primarily in North and South America (neocosmopolite). Within the primary range, in connection with high economic activities and development of transport, new invasion localities have appeared. For the European continent, H. verticillata should be considered a limitedly spreading naturalized neophyte (with the northern border at 55-568 degrees N). In Northern Asia, H. verticillata can probably be considered a tertiary (Eocene) relict, which is currently allocated to the following enclaves: Central Asia-West Siberian, East Siberian (probably formed later), and the largest SE Asian habitats. The northern border of Hydrilla in the Asian continent lies along 56-588 degrees N. Within the Asian part of the range the formation of new foci of infestation is currently observed, the species distribution is not controlled only by abiotic factors (temperature, length of vegetation period, hydrochemical features of the waterbodies), but also by biotic ones; there is a competition with the more aggressive neophyte Elodea canadensis.

A new dioecious species of Tolypella, T. mongolica sp. nov. from the section Tolypella, was described using an integrative taxonomy. It was found in three distant localities – shallows of a brackish small lake and a channel in the midland steppe in Mongolia and the Altai Mountains, and a small brackish water body in the dry steppe in Southeast Europe. It differs from other species in rbcL and ITS sequences and in distinct complex ornamentation of the oospore surface, varying from sparsely coarsely tuberculate to having the appearance of an aerial view of mountain landscape with acute to mostly sharp edges of elements at probably the ripest stage. Wide intrapopulation variability of expression of this trait, only partly explainable by oospore ripening stage, was found and illustrated for two populations, indicating previous underestimation of this phenomenon in taxonomic research. T. mongolica is richly fertile and appears to be ephemeral as most species of this genus. Only female plants were found in all localities. The absence of male plants could be referred to either their earlier development during the growing season or, less likely, parthenogenesis in this species. The description of the new species suggests taxonomic changes for two dioecious species of charophytes. Tolypella porteri stat. et comb. nov. was validated here. T. jwalae was recognized as a species of Nitella, N. jwalae comb. nov.

This first inventory of the charophytes of the Caucasus region was compiled based on records from published references, online sources, a review of herbarium collections, and our own field collections. The documented Caucasian charophyte flora includes 27 species from six genera: 18 Chara species, 6 Nitella, 2 Tolypella, and 1 species each of Lamprothamnium, Nitellopsis, and Sphaerochara. Chara uzbekistanica, C. virgata, and C. contraria var. hispidula are newly recorded for the Caucasus. The high species richness of the genus Chara, the much less diverse genus Nitella, and a few species of Tolypella and Sphaerochara in the Caucasian charophyte flora are typical traits of Palearctic charophyte floras. In total, there are 10 species recorded in Armenia, 16 in Azerbaijan, 18 in Georgia, and 16 in the mountainous region of the North Caucasian Federal District of Russia. Most of the species have wide distributions; none are endemic to the Caucasus. One of the most commonly recorded species in the region, C. gymnophylla, is a usual feature of the Mediterranean and West Asia. The Caucasian charophyte flora can be described as unsurprising from a large-scale perspective, considering its species distribution ranges. However, the association of species makes the region specific at the scale of West Asia when comparing it to its large neighboring areas.