Some of the most vexing problems of deep level relationship that remain in angiosperms involve the superrosids. The superrosid clade contains a quarter of all angiosperm species, with 18 orders in three subclades (Vitales, Saxifragales and core rosids) exhibiting remarkable morphological and ecological diversity. To help resolve deep-level relationships, we constructed a high-quality chromosome-level genome assembly for Tiarella polyphylla (Saxifragaceae) thus providing broader genomic representation of Saxifragales. Whole genome microsynteny analysis of superrosids showed that Saxifragales shared more synteny clusters with core rosids than Vitales, further supporting Saxifragales as more closely related with core rosids. To resolve the ordinal phylogeny of superrosids, we screened 122 single copy nuclear genes from genomes of 36 species, representing all 18 superrosid orders. Vitales were recovered as sister to all other superrosids (Saxifragales + core rosids). Our data suggest dramatic differences in relationships compared to earlier studies within core rosids. Fabids should be restricted to the nitrogen-fixing clade, while Picramniales, the Celastrales-Malpighiales (CM) clade, Huerteales, Oxalidales, Sapindales, Malvales and Brassicales formed an “expanded” malvid clade. The Celastrales-Oxalidales-Malpighiales (COM) clade (sensu APG IV) was not monophyletic. Crossosomatales, Geraniales, Myrtales and Zygophyllales did not belong to either of our well-supported malvids or fabids. There is strong discordance between nuclear and plastid phylogenetic hypotheses for superrosid relationships; we show that this is best explained by a combination of incomplete lineage sorting and ancient reticulation.

Aim: Higher elevation habitats contribute substantially to global biodiversity. Nevertheless, we know comparatively little about how diversity patterns differ among alpine and montane communities across different mountain ranges. Here, we characterized the realized niche space of American seed plants to ask whether or not montane or alpine community compositions define climatically distinct species pools at this regional scale. Location: Americas. Time Period: Contemporary. Major taxa studied: Seed plants. Methods: We assembled a niche model dataset of 72,372 American seed plants based on digitized and georeferenced specimen records. We used this dataset to quantify occupied abiotic niche space with regards to temperature, precipitation, and elevation. This approach further permitted differentiation of higher-elevation specialists (i.e., ranges centered at high elevations) from generalists (i.e., ranges centered at lower elevations but extending into mountain areas). Results: Montane communities did not differ from the regional species pool in terms of richness patterns, occupied climatic niche space, or niche breadth. In contrast, alpine communities were characterized by a bimodal latitudinal diversity gradient, drastically reduced climatic niche space, and broader temperature but narrower precipitation niche breadth. Alpine generalists further showed statistically significant differences in temperature, but not precipitation, niche breadth from both alpine specialists and lowland taxa. We also highlight non-alpine species whose climatic niche space otherwise overlapped with that of alpine plants. These species were geographically concentrated in the southern US and Mexico, tended to have a greater fraction of their ranges in frost-exposed mountain foothills, and less of their range in lowland, frost-free, areas, compared to other non-alpine species. Main conclusions: These results suggest that ecological and physiological barriers, rather than dispersal limitation might better explain alpine community assembly and that alpine, but not montane, communities form a climatically distinct species pool in the Americas.