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...

C(4) photosynthesis is a plant adaptation to high levels of photorespiration. Physiological models predict that atmospheric CO(2) concentration selected for C(4) grasses only after it dropped below a critical threshold during the Oligocene (∼30 Ma), a hypothesis supported by phylogenetic and molecular dating analyses. However the same models predict that CO(2) should have reached much lower levels before selecting for C(4) eudicots, making C(4) eudicots younger than C(4) grasses. In this study, different phylogenetic datasets were combined in order to conduct the first comparative analysis of the age of C(4) origins in eudicots. Our results suggested that all lineages of C(4) eudicots arose during the last 30 million years, with the earliest before 22 Ma in Chenopodiaceae and Aizoaceae, and the latest probably after 2 Ma in Flaveria. C(4) eudicots are thus not globally younger than C(4) monocots. All lineages of C(4) plants evolved in a similar low CO(2) atmosphere that predominated during the last 30 million years. Independent C(4) origins were probably driven by different combinations of specific factors, including local ecological characteristics such as habitat openness, aridity, and salinity, as well as the speciation and dispersal history of each clade. Neither the lower number of C(4) species nor the frequency of C(3)-C(4) intermediates in eudicots can be attributed to a more recent origin, but probably result from variation in diversification and evolutionary rates among the different groups that evolved the C(4) pathway.

SummaryUsing phylogenetics and transcriptomics, we show that independent origins of both CAM and C4 photosynthesis in Caryophyllales co-opted the same genes for PEPC through similar adaptive changes.

• Premise of the study: Despite recent progress, significant uncertainties remain concerning relationships among early-branching lineages within Viburnum (Adoxaceae), prohibiting a new classification and hindering studies of character evolution and the increasing use of Viburnum in addressing a wide range of ecological and evolutionary questions. We hoped to resolve these issues by sequencing whole plastid genomes for representative species and combining these with molecular data previously obtained from an expanded taxon sample.• Methods: We performed paired-end Illumina sequencing of plastid genomes of 22 Viburnum species and combined these data with a 10-gene data set to infer phylogenetic relationships for 113 species. We used the results to devise a comprehensive phylogenetic classification and to analyze the evolution of eight morphological characters that vary among early-branching lineages.• Key results: With greatly increased levels of confidence in most of the early branches, we propose a phylogenetic classification of Viburnum, providing formal phylogenetic definitions for 30 clades, including 13 with names recognized under the International Code of Nomenclature for Algae, Fungi, and Plants, eight with previously proposed informal names, and nine newly proposed names for major branches. Our parsimony reconstructions of bud structure, leaf margins, inflorescence form, ruminate endosperm, extrafloral nectaries, glandular trichomes, palisade anatomy, and pollen exine showed varying levels of homoplasy, but collectively provided morphological support for some, though not all, of the major clades.• Conclusions: Our study demonstrates the value of next-generation plastid sequencing, the ease of creating a formal phylogenetic classification, and the utility of such a system in describing patterns of character evolution.

With about 350 species, Paspalum is one of the richest genera within the Poaceae. Its species inhabit ecologically diverse areas along the Americas and they are largely responsible for the biodiversity of grassland ecosystems in South America. Despite its size and relevance, no phylogeny of the genus as a whole is currently available and infrageneric relationships remain uncertain. Many Paspalum species consist of sexual-diploid and apomicticpolyploid cytotypes, and several have arisen through hybridization. In this paper we explore the phylogenetic structure of Paspalum using sequence data of four noncoding cpDNA fragments from a wide array of species which were combined with morphological data for a subset of diploid taxa. Our results confirmed the general monophyly of Paspalum if P. inaequivalve is excluded and the small genus Thrasyopsis is included. Only one of the four currently recognized subgenera was monophyletic but nested within the remainder of the genus. Some informal morphological groups were found to be polyphyletic. The placement of known allopolyploid groups is generally congruent with previously stated hypotheses although some species with shared genomic formulae formed paraphyletic arrangements. Other species formed a basal grade including mostly umbrophilous or hygrophilous species. It is hypothesized that the genus may have diversified as a consequence of the expansion of C4 grass-dominated grasslands in South America.

The evolutionary accessibility of novel adaptations varies among lineages, depending in part on the genetic elements present in each group. However, the factors determining the evolutionary potential of closely related genes remain largely unknown. In plants, CO2-concentrating mechanisms such as C4 and crassulacean acid metabolism (CAM) photosynthesis have evolved numerous times in distantly related groups of species, and constitute excellent systems to study constraints and enablers of evolution. It has been previously shown for multiple proteins that grasses preferentially co-opted the same gene lineage for C4 photosynthesis, when multiple copies were present. In this work, we use comparative transcriptomics to show that this bias also exists within Caryophyllales, a distantly related group with multiple C4 origins. However, the bias is not the same as in grasses and, when all angiosperms are considered jointly, the number of distinct gene lineages co-opted is not smaller than that expected by chance. These results show that most gene lineages present in the common ancestor of monocots and eudicots produced gene descendants that were recruited into C4 photosynthesis, but that C4-suitability changed during the diversification of angiosperms. When selective pressures drove C4 evolution, some copies were preferentially co-opted, probably because they already possessed C4-like expression patterns. However, the identity of these C4-suitable genes varies among clades of angiosperms, and C4 phenotypes in distant angiosperm groups thus represent genuinely independent realizations, based on different genetic precursors.

No abstract

RESUMENSe ha registrado un total de 146 especies de plantas vasculares, agrupadas en 124 géneros y 52 familias, entre agosto de 1997 y diciembre de 1998. Las magnoliópsidas (dicotiledóneas) fueron el grupo dominante con 115 especies, 96 géneros y 42 familias. Las liliópsidas (monocotiledóneas) estuvieron representadas por 28 especies, 26 géneros y 8 familias. No se registró gimnospermas. Los pteridófitos estuvieron representados por tres especies. Las familias más representativas fueron Asteraceae con 19 especies, Poaceae con 16 y Solanaceae con 13.Palabras claves: Diversidad, flora, El Niño, Lachay. ABSTRACTA total 01. 146 species of vascular plants, grouped in 124 genera and 52 families were recorded, among August 1997 and December 1998. The Magnolliopsidae (Dicotyledoneae) was the, dominan! group with 115 species, 26 genera, and 8 families. There are not records for Gymnosperm. Three species represented the Pteridophy!a. The more representative families were, the Asteraceae with 19 species, Poaceae with 16 species and Solanaceae with 13 species.