Nordenskioldia and Trochodendron (Trochodendraceae) from the Miocene of Northwestern North America
ABSTRACT The extinct trochodendraceous genus Nordenskioldia, well represented in the Paleocene of the Northern Hemisphere, is documented for the first time from the Neogene, based upon infructescences, fruits, associated twigs, and foliage from the Miocene of Idaho, Washington, and southern British Columbia. The infructescences and fruits, assigned to Nordenskioldia interglacialis (Hollick) comb. nov., are very similar to Paleocene N. borealis, but differ in ranging to a higher number of carpels per fruit and in being less regularly dehiscent. The leaves, Zizyphoides auriculata (Heer) comb. nov., formerly attributed to Populus and Cocculus, are clearly congeneric with the leaves associated with Nordenskioldia in Paleocene deposits. Zizyphoides auriculata leaves differ from Paleocene Z. flabellum in having generally more prominent dentations along the margin and a broader divergence of the lateral primary veins. Excellent preservation of the Miocene material reveals features not preserved in the Paleocene specimens, and in particular, lignified fruitlets clearly show aborted ovules in addition to the single mature seed. Infructescences of Trochodendron are also documented from the same Miocene localities at which N. interglacialis occurs. The close similarities between Paleocene and Miocene species of Nordenskioldia, and also between the Miocene and extant species of Trochodendron, suggest relative stasis in the morphological evolution of the Trochodendraceae over intervals of up to 45 million years.
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ABSTRACT: Most angiosperms have gynoecia with two to five carpels. However, more than five carpels (here termed ‘multicarpellate condition’) are present in some representatives of all larger subclades of angiosperms. In such multicarpellate gynoecia, the carpels are in either one or more than one whorl (or series). I focus especially on gynoecia in which the carpels are in a single whorl (or series). In such multicarpellate syncarpous gynoecia, the closure in the centre of the gynoecium is imprecise as a result of slightly irregular development of the carpel flanks. Irregular bumps appear to stuff the remaining holes. In multicarpellate gynoecia, the centre of the remaining floral apex is not involved in carpel morphogenesis, so that this unspent part of the floral apex remains morphologically undifferentiated. It usually becomes enclosed within the gynoecium, but, in some cases, remains exposed and may or may not form simple excrescences. The area within the remaining floral apex is histologically characterized by a parenchyma of simple longitudinal cell rows. In highly multicarpellate gynoecia with the carpels in a whorl, the whorl tends to be deformed into an H-shaped or star-shaped structure by differential growth of the floral sectors, so that carpels become aligned in parallel rows, in which they face each other with the ventral sides. In this way, a fractionated compitum may still be functional. Multicarpellate gynoecia (with the carpels in one whorl or series) occur in at least one species in 37 of the 63 angiosperm orders. In contrast, non-multicarpellate gynoecia are present in at least one species of all 63 orders. The basal condition in angiosperms is more likely non-multicarpellate. Multicarpellate gynoecia are restricted to flowers that are not highly synorganized. In groups with synorganized androecium and gynoecium and in groups with elaborate monosymmetric flowers, multicarpellate gynoecia are lacking. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 174, 1–43.Botanical Journal of the Linnean Society 01/2014; 174(1). · 2.59 Impact Factor
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ABSTRACT: The early-diverging eudicot order Trochodendrales contains only two monospecific genera, Tetracentron and Trochodendron. Although an extensive fossil record indicates that the clade is perhaps 100 million years old and was widespread throughout the Northern Hemisphere during the Paleogene and Neogene, the two extant genera are both narrowly distributed in eastern Asia. Recent phylogenetic analyses strongly support a clade of Trochodendrales, Buxales, and Gunneridae (core eudicots), but complete plastome analyses do not resolve the relationships among these groups with strong support. However, plastid phylogenomic analyses have not included data for Tetracentron. To better resolve basal eudicot relationships and to clarify when the two extant genera of Trochodendrales diverged, we sequenced the complete plastid genome of Tetracentron sinense using Illumina technology. The Tetracentron and Trochodendron plastomes possess the typical gene content and arrangement that characterize most angiosperm plastid genomes, but both genomes have the same unusual ∼4 kb expansion of the inverted repeat region to include five genes (rpl22, rps3, rpl16, rpl14, and rps8) that are normally found in the large single-copy region. Maximum likelihood analyses of an 83-gene, 88 taxon angiosperm data set yield an identical tree topology as previous plastid-based trees, and moderately support the sister relationship between Buxaceae and Gunneridae. Molecular dating analyses suggest that Tetracentron and Trochodendron diverged between 44-30 million years ago, which is congruent with the fossil record of Trochodendrales and with previous estimates of the divergence time of these two taxa. We also characterize 154 simple sequence repeat loci from the Tetracentron sinense and Trochodendron aralioides plastomes that will be useful in future studies of population genetic structure for these relict species, both of which are of conservation concern.PLoS ONE 01/2013; 8(4):e60429. · 3.53 Impact Factor
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ABSTRACT: Some of the evolutionary history of land plants has been documented based on the fossil record and a few broad-scale phylogenetic analyses, especially focusing on angiosperms and ferns. Here, we reconstructed phylogenetic relationships among all 706 families of land plants using molecular data. We dated the phylogeny using multiple fossils and a molecular clock technique. Applying various tests of diversification that take into account topology, branch length, numbers of extant species as well as extinction, we evaluated diversification rates through time. We also compared these diversification profiles against the distribution of the climate modes of the Phanerozoic. We found evidence for the radiations of ferns and mosses in the shadow of angiosperms coinciding with the rather warm Cretaceous global climate. In contrast, gymnosperms and liverworts show a signature of declining diversification rates during geological time periods of cool global climate. This broad-scale phylogenetic analysis helps to reveal the successive waves of diversification that made up the diversity of land plants we see today. Both warm temperatures and wet climate may have been necessary for the rise of the diversity under a successive lineage replacement scenario.BMC Evolutionary Biology 11/2011; 11:341. · 3.29 Impact Factor