~350,000 (representing an estimated 80–90% of the global total) species
||Vellend M et al., Plant Biodiversity Change Across Scales During the Anthropocene. Annu Rev Plant Biol. 2017 Jan 11. doi: 10.1146/annurev-arplant-042916-040949. p.3.5 bottom paragraphPubMed ID28125286
|| Joppa LN, Roberts DL, Pimm SL. 2010. How many species of flowering plants are there? Proc. R. Soc. Lond. B 278: 554–59 doi: 10.1098/rspb.2010.1004.  Pimm SL, Joppa LN. 2015. How many plant species are there, where are they, and at what rate are they going extinct? Ann. Mo. Bot. Gard. 100:170–76 link PubMed ID20610425
||P.3.5 bottom paragraph: "Roughly 350,000 plant species on earth have been named, representing an estimated 80–90% of the global total (primary sources). Since the first vascular plants evolved >400 Mya, global plant diversity has increased markedly. Surprisingly, the periodic mass extinctions observed for animals do not
appear to apply to plants (refs 120, 122). This is one clue that plants might be comparatively resistant
to extinction. Still, plant extinctions have occurred throughout history and can be characterized
by background extinction rates, which help to put the Anthropocene in context. That said, using the fossil record and/or molecular phylogenies to generate extinction and speciation estimates is fraught with uncertainties, and all estimates should be interpreted as very rough approximations. In addition, the types of Anthropocene extinction and speciation events [investigators] have been able to observe (rare island endemics and hybrid polyploid species during the first decades of their existence, respectively) are exactly of the type not represented in the fossil record (refs 40, 80)."