Recent progress in reconstructing angiosperm phylogeny.

In the past year, the study of angiosperm phylogeny has moved from tentative inferences based on relatively small data matrices into an era of sophisticated, multigene analyses and significantly greater confidence. Recent studies provide both strong statistical support and mutual corroboration for crucial aspects of angiosperm phylogeny. These include identifying the earliest extant lineages of angiosperms, confirming Amborella as the sister of all other angiosperms, confirming some previously proposed lineages and redefining other groups consistent with their phylogeny. This phylogenetic framework enables the exploration of both genotypic and phenotypic diversification among angiosperms.

ITS sequence variation within and among populations of Lomatium grayi and L. laevigatum (Umbelliferae).

Nuclear ribosomal RNA genes provide markers for retrieving phylogeny at a variety of taxonomic levels. The internal transcribed spacers (ITS), separating the coding regions, evolve relatively rapidly and may be useful for reconstructing phylogenies at the specific and generic levels. ITS-1, located between the 18S and 5.8S genes, may be especially valuable at the species level and below. However, despite the promise that this region holds for studies below the species level, few studies have addressed levels of ITS-1 variability within and among conspecific populations of plants. To assess the apportionment of ITS-1 sequence variation, a hierarchical sampling strategy was used to compare sequences from individuals within and among populations of Lomatium grayi and L. laevigatum, widespread and restricted congeners of the Umbelliferae, respectively. ITS-1 is 209 bp in length in L. grayi and 200 bp in L. laevigatum. No sequence variation in ITS-1 was observed within populations of either species, and a single population of the more widespread L. grayi differed from the other seven populations by two base substitutions for a sequence divergence of 1.0%. Sequence divergence between L. laevigatum and the common ITS-1 sequence of L. grayi was 1.5%; that between L. laevigatum and the variant of L. grayi was 2.5%. ITS-1 sequences in Lomatium are less variable than either allozymes or chloroplast DNA and do not appear to provide a valuable source of intraspecific markers for population-level studies.(ABSTRACT TRUNCATED AT 250 WORDS)

Structural homology and developmental transformations associated with ovary diversification in Lithophragma (Saxifragaceae).

Lithophragma, comprising only ten species, encompasses a remarkable diversity of ovary positions, reported to range from inferior to superior. The structural homology of the gynoecium and developmental transformations associated with ovary diversification are investigated for Lithophragma. Scanning electron and light microscopy indicate that all species of Lithophragma have epigynous flowers. Lithophragma campanulatum, L. glabrum, and L. heterophyllum have ovaries that externally appear nearly superior, but are actually shallowly inferior or "pseudosuperior." The inferior ovaries of Lithophragma species can be conceptually divided into superior and inferior regions that meet at the point of perianth and androecial insertion. Static and ontogenetic allometry reveal that across the species of Lithophragma the lengths of these two ovary regions are coordinated. Ovary regions in mature flowers display an approximately linear relationship that can be expressed through the allometric equation SL = -0.5314 IL + 2.0348 (where SL and IL are the lengths of the superior and inferior regions of the ovary, respectively; r = 0.7683, df = 35, P = 2.45 × 10). Mapping ontogenetic allometries onto a recent phylogeny for Lithophragma shows that ovary position evolution is bidirectional and has shifted toward greater superiority in some species and greater inferiority in others.

The phylogenetic potential of entire 26S rDNA sequences in plants.

18S ribosomal RNA genes are the most widely used nuclear sequences for phylogeny reconstruction at higher taxonomic levels in plants. However, due to a conservative rate of evolution, 18S rDNA alone sometimes provides too few phylogenetically informative characters to resolve relationships adequately. Previous studies using partial sequences have suggested the potential of 26S or large-subunit (LSU) rDNA for phylogeny retrieval at taxonomic levels comparable to those investigated with 18S rDNA. Here we explore the patterns of molecular evolution of entire 26S rDNA sequences and their impact on phylogeny retrieval. We present a protocol for PCR amplification and sequencing of entire (approximately 3.4 kb) 26S rDNA sequences as single amplicons, as well as primers that can be used for amplification and sequencing. These primers proved useful in angiosperms and Gnetales and likely have broader applicability. With these protocols and primers, entire 26S rDNA sequences were generated for a diverse array of 15 seed plants, including basal eudicots, monocots, and higher eudicots, plus two representatives of Gnetales. Comparisons of sequence dissimilarity indicate that expansion segments (or divergence domains) evolve 6.4 to 10.2 times as fast as conserved core regions of 26S rDNA sequences in plants. Additional comparisons indicate that 26S rDNA evolves 1.6 to 2.2 times as fast as and provides 3.3 times as many phylogenetically informative characters as 18S rDNA; compared to the chloroplast gene rbcL, 26S rDNA evolves at 0.44 to 1.0 times its rate and provides 2.0 times as many phylogenetically informative characters. Expansion segment sequences analyzed here evolve 1.2 to 3.0 times faster than rbcL, providing 1.5 times the number of informative characters. Plant expansion segments have a pattern of evolution distinct from that found in animals, exhibiting less cryptic sequence simplicity, a lower frequency of insertion and deletion, and greater phylogenetic potential.