Opuntioideae, composed of roughly 370 species, occur in almost every biome in the Americas, from seasonally dry tropical forests (SDTF) to high-elevation Andean grasslands, American deserts and temperate zones. The interrelationships among the three major clades of Opuntioideae (Cylindropuntieae, Opuntieae and Tephrocacteae) are not well resolved, and thus, the ancestral habitat, biogeographic history and evolution of morphological characters, such as large photosynthetic leaves and flattened stems, are poorly understood. To test their geographic origin and evolution of key morphological characters, we built the largest phylogenomic dataset for Cactaceae to date using 103 plastid genes of 107 taxa of Opuntioideae. The subfamily Opuntioideae likely evolved in South America in a combination of seasonally dry tropical forest (SDTF)/desert habitats. Opuntieae most likely evolved in South America in SDTF and, from there, moved into desert regions, Chaco and temperate/subtropical zones, while Tephrocacteae and Cylindropuntieae evolved in South America in desert regions and moved into SDTF, Chaco and temperate/subtropical zones. Analyses of morphological evolution suggest that, although large leaves are plesiomorphic in Opuntioideae, long-lived, photosynthetically active leaves in Cylindropuntieae and Tephrocacteae are homoplasious and do not represent retained plesiomorphy, as is often assumed. Flattened stems are synapomorphic for Opuntieae, possibly representing adaptation to competition for light resources in SDTF, their most likely ancestral area.

• Premise of study: Taxonomic circumscription of subspecific taxa within Coryphantha robustispina was evaluated with morphological data and microsatellites. This study was the first to compare adequately sampled morphological and DNA analyses at the population level in the Cactaceae. This comparison was important to test reliability of both methods and to gain a better understanding of phytogeography, evolution, and systematics of the species, knowledge that could prove useful for other taxa as well. Populations of C. robustispina subsp. robustispina are listed as endangered by the U. S. Fish and Wildlife Service. Our primary goal was to explore correlations among geographical distribution, morphology, and genetics of selected populations throughout the range of the species and the outgroup, C. poselgeriana.

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A study was conducted to ascertain the taxonomic validity of the endangered taxon Echinocactus horizonthalonius var. nicholii and whether there may be other groups of populations worthy of subspecies status within the range of the species. To test the hypothesis that individuals of E. horizonthalonius var. nicholii are morphologically distinct from those of the typical variety, a multivariate analysis was done to compare the degree of morphological variation or phenotypic plasticity of stem characters within populations to the variation among populations of E. horizonthalonius throughout its known range. Populations of E. texensis were sampled for outgroup comparison. Discriminant function analysis (DFA) assigning individuals by population showed loose groupings of geographically correlated populations. The DFA assigning individuals to regions or potential subspecific taxa indicated high percentages of correct classification for individuals within populations grouped into the Chihuahuan Desert, Sonoran Desert, and Central Mexican Plateau regions. Taxonomically, these groups correspond to E. horizonthalonius subsp. horizonthalonius (Chihuahuan Desert), E. horizonthalonius var. nicholii (Sonoran Desert), and unnamed taxon of E. horizonthalonius (Central Mexican Plateau). Because these morphological entities are correlated with regional distributions, they are placed here under subspecies, including a newly described taxon, E. horizonthalonius subsp. australis. Because no type for E. horizonthalonius could be located, a neotype is designated.