The Cretaceous-Paleogene (K/Pg) extinction appears to have been geographically heterogeneous for some organismal groups. Southern Hemisphere K/Pg palynological records have shown lower extinction and faster recovery than in the Northern Hemisphere, but no comparable, well-constrained Southern Hemisphere macrofloras spanning this interval had been available. Here, macrofloral turnover patterns are addressed for the first time in the Southern Hemisphere, using over 3,500 dicot leaves from the latest Cretaceous (Maastrichtian) and the earliest Paleocene (Danian) of Argentine Patagonia. A maximum ca. 90% macrofloral extinction and ca. 45% drop in rarefied species richness is estimated across the K/Pg, consistent with substantial species-level extinction and previously observed extirpation of host-specialized leaf-mines. However, prior palynological and taxonomic studies indicate low turnover of higher taxa and persistence of general floral composition in the same sections. High species extinction, decreased species richness, and homogenous Danian macrofloras across time and facies resemble patterns often observed in North America, but there are several notable differences. When compared with boundary-spanning macrofloras at similar absolute paleolatitudes (ca. 50⁰S or N) from the Williston Basin (WB) in the Dakotas, both Maastrichtian and Danian Patagonian species richness are higher, extending a history of elevated South American diversity into the Maastrichtian. Despite high species turnover, our analyses also reveal continuity and expansion of leaf morphospace, including an increase in lobed and toothed species unlike the Danian WB. Thus, both Patagonian and WB K/Pg macrofloras support a significant extinction event, but they may also reflect geographically heterogeneous diversity, extinction, and recovery patterns warranting future study.

This dataset contains a full inventory of curated and morphotyped leaf specimens studied in Stiles et al. 2020 (Paleobiology), currently located at the Museo Paleontológico Egidio Feruglio, as well as character matrices and results for cuantitative analyses. Danian specimens and morphotypes largely correspond to those published by Iglesias et al (2007, Geology) and Donovan et al. (2016, Nature Ecol Evo; 2018, Ameghiniana), with revised Maastrichtian morphotypes (revised from Donovan et al. 2016; 2018).  

• Supplementary Table 1. Taxonomically studied macrofloral elements of the Maastrichtian Lefipán and Danian Salamanca and Peñas Coloradas formations. 
• Supplementary Table 2. Shared palyno-species among the Maastrichtian (M) -Danian (D) strata of the Lefipán (Lef) Formation San Ramón section and the Danian Salamanca (Sal) Palacio de los Loros and Bosque Ormachea localities. Compiled from Barreda et al. (2012), Clyde et al. (2014), and Barreda (pers. comm.). 1=present, 0=absent.
• Supplementary Table 3. Inventory of observed specimens for Maastrichtian Lefipán and Danian Salamanca and Peñas Coloradas formations and corresponding localities, curated at the MEF. Specimens denoted using repository number (MPEF-Pb) or unique field number as marked on specimen. 
• Supplementary Table 4. Maastrichtian (left) and Danian (right) dicot leaf morphotypes, exemplar specimens as curated in the MEF, specimen counts per locality and taxonomic affinity if available based on Iglesias et al. (2007; for Danian morphotypes). New Danian morphotypes added by Donovan (2016) marked with an *.   
• Supplementary Table 5. Character states and corresponding numerical code used to build morphological character matrix. Based on Manual of Leaf Architechture (Ellis et al., 2009). "NA" = not applicable.
• Supplementary Table 6. Morphological character matrix coded for each Maastrichtian and Danian morphotype (see Supplementary Table 3) based on characters listed in Supplementary Table 5 (C=character number). "NA" = not applicable.
• Supplementary Table 7. Proportion of missing character data (coded as NA in character matrix: Table S6) for each character as percentage of all morphorypes, and per morphotype as percentage of characters not preserved in the specimens analyzed. Reported following recommendations by Gerber (2019).
• Supplementary Table 8. Disparity measures calculated for representative assemblages of the Lefipán (LEF localities), Salamanca (PL1 and PL2) and Peñas Coloradas (LF) formations, and overall Maastrichtian and Danian floral assemblages.