Opuntia s.s. is a well-supported clade that includes Nopalea. The clade originated in southwestern SA, but the NA radiation was the most extensive, resulting in broad morphological diversity and frequent species formation through reticulate evolution and polyploidy.

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Transcriptomes are useful both for species-tree inference and for uncovering evolutionary complexity within lineages. Through analyses of gene-tree conflict and multiple methods of species-tree inference, we demonstrate that phylogenomic data can provide unparalleled insight into the evolutionary history of Caryophyllales. We also discuss a method for overcoming computational challenges associated with homolog clustering in large data sets.

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27Survival in harsh environments is associated with several adaptations in plants. Species in the 28 Portulacineae (Caryophyllales) have adapted to some of the most extreme terrestrial conditions on 29 Earth, including extreme heat, cold, and salinity. Here, we generated 52 new transcriptomes and 30 combined these with 30 previously generated transcriptomes, forming a dataset containing 68 species 31 of Portulacinaeae, seven from its sister clade Molluginaceae, and seven outgroups. We performed a 32 phylotranscriptomic analysis to examine patterns of molecular evolution within the Portulacineae. Our 33 inferred species tree topology was largely congruent with previous analyses. We also identified several 34 nodes that were characterized by excessive gene tree conflict and examined the potential influence of 35 outlying genes. We identified gene duplications throughout the Portulacineae, and found corroborating 36 evidence for previously identified paleopolyploidy events along with one newly identified event 37

Giant saguaro (Carnegiea gigantea) is one of the longest‐lived and massive cacti species in the Americas. They occur throughout the Sonoran Desert region with a distribution spanning a five‐fold gradient in mean annual precipitation. Relationships between fitness traits, including stem growth, and spatio‐temporal climate patterns are still poorly understood in saguaro, but are assumed to be largely coupled to summer precipitation. To better understand patterns of climate sensitivity in giant saguaro, annual stem growth, carbon isotope ratios (δ13C) in spine tissues, and seasonal variation in stem volume, a proxy for stem water storage, were evaluated over a single growing season (2014) in six widely distributed populations in the northern Sonoran Desert, and over four consecutive growing seasons (2013–2016) in two populations with differences in mean annual precipitation and site moisture (Mi), defined as precipitation amount divided by mean atmospheric vapor pressure deficit. We hypothesized that saguaro growth and δ13C would be coupled to a complex suite of climate conditions that include winter precipitation and aridity. Annual stem growth of all populations was generally better correlated to Mi than precipitation alone and was best correlated with Mi measured over the hydrologic year, October 2013–September 2014 (F = 39.8, P < 0.0001). Likewise, mean δ13C increased with Mi, with the highest correlation with Mi calculated for July 2013–August 2014 (F = 38.4.0, P < 0.0001). Annual stem growth measured across all populations was well correlated to δ13C in spines produced during the current year of growth (F = 36.3, P < 0.0001). Annual variation in stem growth appeared to reflect annual variation in mean stem volume measured monthly from the summer of the previous year to the summer of the current year of growth. Results suggest that stem growth and photosynthetic physiology recorded by δ13C are coupled to a complex suite of climate conditions with a strong legacy effect from the previous summer and winter. These findings provide new insight on the effects of summer and winter drought and a warming climate on the photosynthesis, growth, and fitness of giant saguaro.

Background The plant family Cactaceae provides some of the most striking examples of adaptive evolution, expressing undeniably the most spectacular New World radiation of succulent plants distributed across arid and semi-arid regions of the Americas. Cacti are widely regarded for their cultural, economic and ecological value, yet they are also recognized as one of the most threatened and endangered taxonomic groups on the planet. Scope This paper reviews current threats to species of cacti that have distributions in arid to semi-arid subtropical regions. Our review primarily focuses on four global change forces: 1) increases in atmospheric CO2 concentrations, 2) increases in mean annual temperatures and heat waves, 3) increases in the duration, frequency and intensity of droughts, 4) and increases in competition and wildfire frequency from non-native species invasion. We provide a broad range of potential priorities and solutions for stemming the extinction risk of cacti species and populations. Conclusions Mitigating ongoing and emerging threats to cacti will require not only strong policy initiatives and international cooperation, but also novel and creative approaches to conservation. These approaches include determining at risk species from climate extremes, enhancing habitat quality following disturbance, approaches and opportunities for ex-situ conservation and restoration, and the potential use of forensic tools for identifying plants that have been illegally removed from the wild and sold on open markets.