Phylogenetics and the evolution of major structural characters in the giant genus Euphorbia L. (Euphorbiaceae)

Department of Botany, Smithsonian Institution, NMNH MRC-166, P.O. Box 37012, Washington, DC 20013-7012, USA.
Molecular Phylogenetics and Evolution (Impact Factor: 3.92). 01/2012; 63(2):305-26. DOI: 10.1016/j.ympev.2011.12.022
Source: PubMed

ABSTRACT Euphorbia is among the largest genera of angiosperms, with about 2000 species that are renowned for their remarkably diverse growth forms. To clarify phylogenetic relationships in the genus, we used maximum likelihood, bayesian, and parsimony analyses of DNA sequence data from 10 markers representing all three plant genomes, averaging more than 16kbp for each accession. Taxon sampling included 176 representatives from Euphorbioideae (including 161 of Euphorbia). Analyses of these data robustly resolve a backbone topology of four major, subgeneric clades--Esula, Rhizanthium, Euphorbia, and Chamaesyce--that are successively sister lineages. Ancestral state reconstructions of six reproductive and growth form characters indicate that the earliest Euphorbia species were likely woody, non-succulent plants with helically arranged leaves and 5-glanded cyathia in terminal inflorescences. The highly modified growth forms and reproductive features in Euphorbia have independent origins within the subgeneric clades. Examples of extreme parallelism in trait evolution include at least 14 origins of xeromorphic growth forms and at least 13 origins of seed caruncles. The evolution of growth form and inflorescence position are significantly correlated, and a pathway of evolutionary transitions is supported that has implications for the evolution of Euphorbia xerophytes of large stature. Such xerophytes total more than 400 species and are dominants of vegetation types throughout much of arid Africa and Madagascar.

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    • "Molecular phylogenetic studies (the most recent and comprehensive by Horn et al., 2012) have revealed four main evolutionary lineages in Euphorbia, corresponding to the four subgenera currently recognized. Most species in Europe belong to Euphorbia subgenus Esula Pers., which is sister to all other subgenera (Horn et al., 2012). It comprises roughly 480 species and represents the most significant radiation of the genus in temperate areas of the Old World, with highest diversity in the Mediterranean and the Irano-Turanian regions (Riina et al., 2013). "
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    ABSTRACT: The leafy spurges, Euphorbia subgenus Esula, have one of their diversity centres in the Mediterranean, which is considered to be one of the 25 biodiversity hot-spots. The eastern Mediterranean, in particular, is characterized by its high species richness and is therefore considered to be a cradle for lineage diversification. However, the area remains neglected in phylogenetic studies. Using nuclear ribosomal internal transcribed spacer (ITS) and plastid trnT-trnF sequences, we explored the phylogenetic relationships in the predominantly eastern Mediterranean E. hierosolymitana group, which is characterized by a woody habit. The widespread shrublets E. acanthothamnos, E. glabriflora and E. spinosa, which are similar in habit, are not most closely related, the last two forming a sister clade to other taxa. From the E. acanthothamnos alliance, dendroid shrubs evolved at least two, but possibly four, times, giving rise to widespread E. bivonae and E. hierosolymitana, the Cretan endemic E. sultan-hassei and the here newly described and genetically most divergent E. lemesiana, endemic to Cyprus. We provide a taxonomic treatment and morphological comparison with the similar, but not most closely related, E. hierosolymitana. Our study underlines the phytogeographical peculiarity of Cyprus and contributes to our current knowledge on the diversification patterns in the eastern Mediterranean. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, ●●, ●●–●●.
    Botanical Journal of the Linnean Society 09/2015; 179(2). DOI:10.1111/boj.12319 · 2.53 Impact Factor
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    • "This flora, which is currently quite fragmented, would benefit from detailed exploration (Cowling et al., 2005; Schrire et al., 2005a). It is a relatively old flora, and radiations started in the Oligocene/Early Miocene in Euphorbia (Bruyns et al., 2011; Horn et al., 2012; Peirson et al., 2013) and Commiphora (Weeks and Simpson, 2007). There appears to be an interplay between dispersal among the arid habitats in Africa and repeated, local, radiations, illustrated well in the stem-succulent stapeliads (Bruyns et al., 2014) and the Rutaceae genus Thamnosma (Thiv et al., 2011). "
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    ABSTRACT: Sub-Saharan Africa includes some 45,000 plant species. The spatial patterns of this diversity have been well explored. We can group the species into a set of biogeographical regions (largely co-incident with regions defined for terrestrial vertebrate groups). Furthermore, we know that the diversity is unevenly distributed, with southern Africa (especially the south-western tip) disproportionally species rich, while the West African interior is disproportionally species poor. However, the origins of this diversity have only been explored for two anomalous African Floras (the Tropic-alpine Flora and the Cape Flora), whereas the origins of the diversity of the other floras are still unknown. Here I argue that six floras, with distinct geographical centers, different extra-African affinities, ages of radiation and radiation rates, can be delimited: the Austro-temperate, Tropic-alpine, Lowland forest, Tropic-montane, Savanna and Arid Floras. The oldest flora may be the Lowland forest Flora, and the most recent is the Tropic-alpine, which probably evolved during the Plio-Pleistocene on the summits of the East Africa volcanoes. My results suggest that the most rapidly radiating flora is the Austro-temperate Flora, while the other floras are all diversifying at more or less the same rate, this is also consistent with the current massive species richness in this flora (about half of the African species richness). The Austro-temperate Flora appears to be related to the floras of the other southern continents, the Tropic-alpine Flora to that of the Northern Hemisphere, and the four tropical floras to the tropical regions of the other continents, consistent with the theory of phylogenetic niche conservatism. Current African diversity may be the result of the sequential adding of new floras to the continent. Possibly the species poverty especially of the Lowland forest Flora may be the result of the spread of C4 grasslands and associated regular fires.
    07/2014; 2. DOI:10.3389/fevo.2014.00038
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    • "). Boissier (1862) placed most species of leafy spurges in E. section Tithymalus, but his concept of that large section also included species or subsections that have now been shown to belong to each of the other three subgenera of Euphorbia (Steinmann & Porter, 2002; Horn et al., 2012; Yang et al., 2012; Dorsey et al., 2013; Peirson et al., 2013). Following the recent revision of subgenus Esula by Riina et al. (2013), section Tithymalus has been redefined as the group encompassing its type species, E. peplus L. and closely related species from both the New and Old Worlds (Fig. 1). "
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    ABSTRACT: The 480 species of leafy spurges, Euphorbia subgenus Esula, represent the main temperate radiation in the large genus Euphorbia. This group is distributed primarily in temperate Eurasia, but with smaller, disjunct centres of diversity in the mountains of the Old World tropics, in temperate southern Africa and in the New World. The majority of New World diversity (32 species) occurs in a single section, section Tithymalus. We analysed sequences of the nrITS and plastid ndhF, trnH-psbA, trnS-trnG and trnD-trnT regions to reconstruct the phylogeny of section Tithymalus and to examine the origins and diversification of the species native to the New World. Our results indicate that the New World species of section Tithymalus form a clade that is sister to the widespread, weedy E. peplus. The New World species fall into two primary groups: a ‘northern annual clade’ from eastern North America and a diverse clade of both annual and perennial species that is divided into three subgroups. Within the second group, there is a small ‘southern annual clade’ from Texas and northern Mexico, a perennial ‘Brachycera clade’ from the western United States and northern Mexico, and a perennial ‘Esuliformis clade’ from montane areas of Mexico, Guatemala, Honduras and the Caribbean island of Hispaniola. Ancestral state reconstructions indicate that the annual habit probably evolved in the ancestor of E. peplus and the New World clade, with a subsequent reversal to the perennial habit. In conjunction with this phylogenetic framework, the New World species of section Tithymalus are comprehensively reviewed. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, ●●, ●●–●●.
    Botanical Journal of the Linnean Society 06/2014; 175(2). DOI:10.1111/boj.12167 · 2.53 Impact Factor
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