There are several factors here. Firstly, the flora of most of Russia is relatively sparse. If you look separately at observations of the floristically richer Russian Caucasus, Altai Mountains or Russian Far East, the percentage of RG will be lower (find Доля бэклога в структуре данных in this ).
Most observations of plants in Russia were made not by random people with smartphones, but by active project participants who know how to photograph a plant so that it can be identified, they are familiar with regional binary keys and can find a description of the plant online. For example, before I got to iNat, I participated in a similar Russian website for several years. The core of the identifiers are professional botanists, herbarium workers, teachers and graduate students of universities, or enthusiastic regional amateurs. And also identifiers from Europe and Asia, of course.Identifier statistics
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