The cacti are one of the most celebrated radiations of succulent plants. There has been much speculation about their age, but progress in dating cactus origins has been hindered by the lack of fossil data for cacti or their close relatives. Using a hybrid phylogenomic approach, we estimated that the cactus lineage diverged from its closest relatives ≈35 million years ago (Ma). However, major diversification events in cacti were more recent, with most species-rich clades originating in the late Miocene, ≈10-5 Ma. Diversification rates of several cactus lineages rival other estimates of extremely rapid speciation in plants. Major cactus radiations were contemporaneous with those of South African ice plants and North American agaves, revealing a simultaneous diversification of several of the world's major succulent plant lineages across multiple continents. This short geological time period also harbored the majority of origins of C 4 photosynthesis and the global rise of C 4 grasslands. A global expansion of arid environments during this time could have provided new ecological opportunity for both succulent and C 4 plant syndromes. Alternatively, recent work has identified a substantial decline in atmospheric CO 2 ≈15-8 Ma, which would have strongly favored C 4 evolution and expansion of C 4 -dominated grasslands. Lowered atmospheric CO 2 would also substantially exacerbate plant water stress in marginally arid environments, providing preadapted succulent plants with a sharp advantage in a broader set of ecological conditions and promoting their rapid diversification across the landscape.climate change | paleobotany | CAM photosynthesis P lants are generally classified as succulent when they exhibit pronounced water storage in one or more organs. High degrees of succulence are most often associated with a suite of other characteristics that together confer survival in water-limited environments. This "succulent syndrome" usually includes a shallow root system that permits rapid uptake of unpredictable precipitation; a thick, waxy cuticle that prevents excessive water loss; and Crassulacean acid metabolism (CAM), an alternative photosynthetic pathway that allows plants to uptake atmospheric CO 2 at night when water loss is minimized (1). Although some 30 plant lineages have been classified as succulent, only a small subset of those are species-rich and ecologically important elements of arid and semiarid ecosystems worldwide. These lineages include the ice plants (Aizoaceae, ≈2,000 spp), the spurges (Euphorbia, ≈2,100 spp., ≈650 of which are succulent), the stonecrops (Crassulaceae, ≈1,400 spp.), the aloes (Aloe, ≈400 spp.), the agaves (Agave, ≈200 spp.), the stapeliads and asclepiads (Apocynaceae-Asclepiadoideae, ≈3,700 spp., ≈1,150 of which are succulent) and especially the cacti (Cactaceae, ≈1,850 spp.) (2).The cacti represent the most spectacular New World radiation of succulent plants. Most cacti exhibit a highly specialized life form, with extremely succulent, photosynthetic stems and leaves that have been mo...

Aim: Climatic oscillations have been suggested to promote speciation and changes in species distributions, mostly in connection with the Last Glacial Maximum (LGM).However, the LGM is just the most recent of the 20+ glacial-interglacial periods that characterise the Quaternary. Here, we investigate the role of climatic changes and geomorphological features in shaping the evolution, distribution and population dynamics of the South American cactus Cereus hildmannianus.Location: South-eastern South America. Methods:We built a large fossil-calibrated phylogeny for cacti (family Cactaceae), comprising 128 species distributed in all subfamilies, using a Bayesian relaxed clock.We used the results to derive a secondary calibration for a population-level phylogeny in C. hildmannianus. We amplified two plastid (trnQ-5 0 rps16 and psbJ-petA) and one nuclear marker (PhyC) for 24 populations. We estimated population dynamics, ancestral areas, and species distribution models to infer the clade's evolutionary history in time and space.Results: Our results show a major population divergence of C. hildmannianus at c. 2.60Ma, which is strikingly coincident with the transition of the Pliocene-Pleistocene and onset of Quaternary glaciations. This was followed by a complex phylogeographic scenario involving population expansions across ecologically diverse regions.Main conclusions: Contrary to the dominant research focus on the LGM, our study indicates a major impact of the first Quaternary glaciation on the distribution and population divergence of a South American plant species. Further intraspecific events seem related to successive climatic changes and geomorphology, including the development of the coastal plain and its peculiar diversity. We propose that the first Quaternary glaciation acted as a major evolutionary bottleneck, whereby many warm-adapted lineages succumbed, while those that survived could diversify and better cope with subsequent climatic oscillations.

Types and the number of stomata in the following Arum species: Arum italicum Mill., Arum maculatum var. maculatum L. and Arum maculatum var. immaculatum L., Arum alpinum var. pannonicum Terpo. and Arum alpinum var. intermedium Schur. in three different locations in Zablaće, Normanci and Bilje were investigated. The most prevalent stomata type at both upper and lower epidermis for each Arum species was mostly stomata type paracytic, followed by hexacytic, tetracytic or brachyparacytic as far as locality is concerned. Helicocytic type was more prevalent in Arum alpinum var. pannonicum Terpo. and Arum alpinum var. intermedium Schur. at Bilje. Other stomata types were very rare. A striking regularity in the occurrence of stomata types was not found within a single species. Some stomata types, however, were found either at adaxial or abaxial epidermis or were not present at all. The number of stomata per square mm varied from 25 to 651. A statistically significant difference in the number of stomata per square mm at upper and lower epidermis among Arum species was determined in locations Zablaće and Normanci, whereas no statistically significant differences were found in location Bilje.

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Karyological and molecular studies were done in this paper on three species of genus Arum; Arum italicum Mill. and Arum maculatum L., with two varieties, and Arum alpinum Schott and Kotschy, also with two varieties. The main goal of this paper was to establish whether they were regularly determined exclusively on the principle of morphological parameters. Karyological studies showed that the number of chromosomes for Arum italicum Mill. amounted to 2n=84, for Arum maculatum L. 2n=56 and for Arum alpinum Schott and Kotschy 2n=28. This confirmed that these species are not only clean and separated, but also support the regularity of the morphological determination. Molecular studies, e.g. RAPD method showed that two genetically separated species groups correspond to the three mentioned species. Arum italicum Mill. is the least homogenous species closely related and the variability between populations is high. Arum maculatum L. is more homogenous within the species, two varieties could be differentiated whereas they are closely genetically related and the variability between the populations is too high. Arum alpinum is strongly homogenous and within these species two varieties could also be differentiated. That means that they are closely related and the variability between the populations is very high. These observations mostly coincided with previous morphological investigations

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