Macrophytes (macroscopic water plants) are primary producers that act as a food resource and supply habitat structure for other aquatic organisms. The highest alpha  diversity of macrophytes was in Fennoscandian lakes. Alpha diversity was lowest at high latitudes and remote locations such as the Canadian High Arctic, Greenland, Iceland, and the Kola Peninsula. Three of the ecoregions with the lowest species richness had an average latitude > 701°N, suggesting that alpha diversity of macrophytes declines in high-latitude Arctic regions. The most common taxa across all stations were Myriophyllum alterniflorum, Potamogeton gramineus, and Ranunculus reptans. Aquatic moss species comprised a higher percentage of total species richness with increasing latitude.

Potamogeton gramineus (pondweed). Photo: Mps197/Shutterstock.comPotamogeton gramineus (pondweed). Photo: Mps197/ alternate water-milfoil (Myriophyllum alterniflorum). Photo: Mps197/Shutterstock.comalternate water-milfoil (Myriophyllum alterniflorum). Photo: Mps197/

For most ecoregions, turnover was the dominant component of beta diversity as it accounted for more than 70% of the total beta diversity. This indicates that variation in diversity within an ecoregion was due to finding different species across stations, and emphasizes the importance of increasing sample coverage. Beta diversity of macrophyte assemblages ranged between 0 (no inter-station differences in species composition) and 1 (no inter-station overlap in species) within the ecoregions. Macrophyte beta-diversity was largely driven by ecoregion connectivity, with remote ecoregions generally having lower beta diversity.

 Partially submerged vegetation, Rybachy Peninsula near Murmansk, Russia. Photo: svic/Shutterstock.comPartially submerged vegetation, Rybachy Peninsula near Murmansk, Russia. Photo: svic/ Alternate water-milfoil (Myriophyllum alterniflorum). Photo: Mps197/Shutterstock.comAlternate water-milfoil (Myriophyllum alterniflorum). Photo: Mps197/

Extensive macrophyte data were available for some areas of the Arctic (e.g., Fennoscandia), but data were sparse for large areas of Canada, Alaska, and Russia. Macrophyte monitoring is not part of regular assessments in Canada, Alaska, and Russia, thus limiting the spatial scope of available data. Across the entire circumpolar region, there are very few lakes that are monitored regularly. As a result, time series data are generally not available, and many lake observations are outdated (e.g., 1970s or earlier) with no repeated visits to the same lakes. Such data do not allow for the detection of shifts in macrophyte distribution and may not provide an accurate view of contemporary patterns in diversity. Moreover, monitoring may not include the identification or enumeration of aquatic mosses, helophytes, or bryophytes, which may be of particular concern if these groups are dominant in a region, as often occurs in the sub- and high Arctic. Improvements to the monitoring of macrophytes are  necessary across the circumpolar region, and should focus on regular and repeated monitoring of representative lakes with standardized monitoring protocols.

Wetlands in Canadian tundra. Photo: chbaum/Shutterstock.comWetlands in Canadian tundra. Photo: chbaum/ Duckweed, Lemna. Photo: SrjT/Shutterstock.comDuckweed, Lemna. Photo: SrjT/

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