Included: 6.850 currently recognized taxa of uncertain status, tagged as "provisionally accepted" - in average about 50% of them will later keep their status as accepted. Almost half of the provisionally accepted names (2.652) are - mostly French - microspecies in Rubus.
Not included: about 25.000 - 35.000 doubtful names flagged as "unplaced".
Included: 13.608 microspecies mostly in apomictic genera: Ranunculus auricomus agg. (Ranunculaceae) (941), Rubus fruticosus agg. (Rosaceae) (3.172), Alchemilla (Rosaceae) (695), Sorbus s. l. (Rosaceae) (213), Hieracium and Pilosella (Asteraceae) (5.271), Taraxacum officinale agg. (Asteraceae) (2.389), Limonium (530) and others (268, of them many Cotoneaster).
Between 2.300 and 2.700 new species were described each year during the years 2012 - 2020 (Govaerts, in litt.) and are subsequently registered in IPNI; the trend was quite stable. The total number of species does not increase by the same amount because at the same time other, previously listed as valid, doubtful species are recognized as synonyms, leading to an increase of between 1.000 - 2.000 per year in the grand total.
Therefore between 352.000 and 357.000 (including microspecies) is the correct number of currently recognized higher plant species (past 1753), increasing by about 1.500 - 2.000 each year (after subtraction of newly recognized synonymies). About +/- 10.000 tolerance exists, based on differing species concepts (lumping vs. splitting). The real number is probably closer to 352.000 because there still remain some doubtful taxa waiting to be synonymized.
Nic Lugadha et al. (2016) arrive through "extrapolation" at a total of 390.000: clearly too high and nowhere within our "bottom-up", checklist-based numbers. This number was adjusted to a more realistic 350.396 in the 2023 "State of the World's Plants and Fungi" by Kew.
The total number of non-fossil, higher plant species - including the undescribed ones - will probably not exceed 400.000 by much.