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While the fundamental biophysics of C 3 photosynthesis is highly conserved across plants, substantial leaf structural and enzymatic variation translates into variability in rates of carbon assimilation. Although this variation is well documented, it remains poorly understood how photosynthetic rates evolve, and whether macroevolutionary changes are related to the evolution of leaf morphology and biochemistry. A substantial challenge in large-scale comparative studies is disentangling evolutionary adaptation from environmental acclimation. We overcome this by using a ‘macroevolutionary common garden’ approach in which we measured metabolic traits ( J max and V cmax ) from 111 phylogenetically diverse species in a shared environment. We find substantial phylogenetic signal in these traits at moderate phylogenetic timescales, but this signal dissipates quickly at deeper scales. Morphological traits exhibit phylogenetic signal over much deeper timescales, suggesting that these are less evolutionarily constrained than metabolic traits. Furthermore, while morphological and biochemical traits (LMA, N area and C area ) are weakly predictive of J max and V c max , evolutionary changes in these traits are mostly decoupled from changes in metabolic traits. This lack of tight evolutionary coupling implies that it may be incorrect to use changes in these functional traits in response to global change to infer that photosynthetic strategy is also evolving.

Phenology is changing in response to anthropogenic climate change (Parmesan and Yohe, 2003) and understanding exactly how phenological shifts track changing environmental conditions can help prioritize mitigation as well as management actions (Morellato et al., 2016). For example, if we can predict the phenology of recently arrived invasive species based on their closest relatives, we can narrow down treatment windows for manual removal or herbicide application.Phenological studies of flowering plants use combinations of historical observations and herbarium specimens to track changes in leaf, floral, and fruiting phenology (Primack et al., 2004;Munson and Long, 2017;Willis et al., 2017;Meineke et al., 2019). The multiple lifetimes of collection efforts housed in herbaria span space and time, and provide irreplaceable insight into long-term trends and broadscale patterns of changes in phenology (

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For many species, understanding how climate influences the timing of seasonal life history events (phenology) is limited by the availability of long-term data. Further, long-term studies of plant phenology are often local in scale. Recent efforts to digitize herbarium collections make it possible to examine large numbers of specimens from multiple species over broad geographic regions. In the Pacific Northwest (PNW), understory plant species found in oldgrowth forests may be buffered against climate warming (Frey et al. 2016). Using 8,500 specimens of 40 plant species housed in 25 herbaria collected over more than 100 years in the PNW we analyzed whether these species have experienced shifts in flowering phenology corresponding to long-term climate warming. Our findings were mixed, with some species experiencing earlier flowering phenology over time while others have not shifted their flowering phenology since the early-1900s. Responses were dependent on life-history, including habitat preference and timing of flowering. These results demonstrate that herbarium collections are an important tool for examining long-term flowering phenological over broad geographic areas and habitat types.