Recent efforts to improve the representation of plant species included on the IUCN Red List of Threatened Species through the IUCN Sampled Red List Index (SRLI) for Plants have led to the assessment of almost 1000 additional species of pteridophytes and lycophytes under IUCN Red List criteria. Species were selected at random from all lineages of pteridophytes and lycophytes and are taxonomically as well as ecologically representative of pteridophyte and lycophyte diversity. 16% of pteridophyte and lycophyte species are globally threatened with extinction and 22% are of elevated conservation concern (threatened or Near Threatened); of species of pteridophytes and lycophytes previously included on the Red List, 54% were considered threatened. Over half of pteridophyte and lycophyte species assessed for the SRLI use estimates of range size; therefore the method used to measure range may affect the Red List category assigned. We evaluated this using two alternative metrics for estimating range, species distribution modelling (SDM) and ecologically suitable habitat (ESH), for 227 species endemic to the Neotropical biogeographic realm. Differences between range estimates were small when ranges were small but increased with increasing range size. For 58 (25.6%) species alternative modelling techniques result in the species meeting the threshold for a different IUCN Red List category from using extent of occurrence. Modelling threatened species distributions also highlights priority areas for conservation in tropical and subtropical montane forests that are the most species-rich habitat for small-range pteridophyte and lycophyte species, but which are now increasingly subject to rapid conversion to agriculture.Key words: ecologically suitable habitat, IUCN Red List, lycophytes, pteridophytes, Sampled Red List Index, species distribution modelling, SRLI for Plants.Attempts to set, measure and monitor progress towards international goals to address biodiversity loss (Balmford et al., 2005;Walpole et al., 2009) have to date largely been unsuccessful (Butchart et al., 2010;Tittensor et al., 2014). The outcome of the Xth Conference of the Parties to the Convention on Biological Diversity (CBD) in 2010 was an agreement on a further 20, more stringent, 'Aichi' Targets (Decision X/2; UNEP, 2010). As a component of this effort, the IUCN Red List Index (Butchart et al., 2004(Butchart et al., , 2005 and its sampled approach for larger, more poorly-known taxonomic groups has been implemented as a formal CBD indicator, a Barometer of Life (Stuart et al., 2010) measuring Aichi Target 12: "By 2020 the extinction of known threatened species has been prevented and their conservation status, particularly of those most in decline, has been improved and sustained" (UNEP, 2010). To monitor the conservation status and trends in extinction risk for plants worldwide and help measure progress in achieving Aichi Target 12, samples of different plant lineages have been selected and assessed for the IUCN Sampled Red List Index (SRLI) fo...