Catarina Rydin

Phylogenetic relationships in the order Ericales s.l.: analyses of molecular data from five genes from the plastid and mitochondrial genomes

Phylogenetic interrelationships in the enlarged order Ericales were investigated by jackknife analysis of a combination of DNA sequences from the plastid genes rbcL, ndhF, atpB, and the mitochondrial genes atp1 and matR. Several well-supported groups were identified, but neither a combination of all gene sequences nor any one alone fully resolved the relationships between all major clades in Ericales. All investigated families except Theaceae were found to be monophyletic. Four families, Marcgraviaceae, Balsaminaceae, Pellicieraceae, and Tetrameristaceae form a monophyletic group that is the sister of the remaining families. On the next higher level, Fouquieriaceae and Polemoniaceae form a clade that is sister to the majority of families that form a group with eight supported clades between which the interrelationships are unresolved: Theaceae-Ternstroemioideae with Ficalhoa, Sladenia, and Pentaphylacaceae; Theaceae-Theoideae; Ebenaceae and Lissocarpaceae; Symplocaceae; Maesaceae, Theophrastaceae, Primulaceae, and Myrsinaceae; Styracaceae and Diapensiaceae; Lecythidaceae and Sapotaceae; Actinidiaceae, Roridulaceae, Sarraceniaceae, Clethraceae, Cyrillaceae, and Ericaceae.

SEED PLANT RELATIONSHIPS AND THE SYSTEMATIC POSITION OF GNETALES BASED ON NUCLEAR AND CHLOROPLAST DNA: CONFLICTING DATA, ROOTING PROBLEMS, AND THE MONOPHYLY OF CONIFERS

We investigated the systematic position of Gnetales and other seed plant groups using molecular data from 119 land plant species. More than 100 new sequences of rbcL, atpB, 26S, and 18S ribosomal DNA were analyzed together with available GenBank sequences. To evaluate thoroughly the phylogenetic information of each gene, the four data sets were analyzed both separately and combined using different character coding. We found no supported conflict between codon positions in the plastid sequences, but we found a more complex pattern, indicating conflict between transitions and transversions, within each position. Including all information, plastid data results in a “Gnetales basal” phylogeny, whereas nuclear data weakly supports anthophytes. When transitions are excluded, Gnetales associate with conifers. Our study does not answer all questions on seed plant phylogeny, but it does show conifers as monophyletic with high support, rejecting a close relationship between Gnetales and the conifer family Pinaceae. Nuclear and chloroplast data produced essentially identical phylogenies except for the position of the seed plant root, and a sister relationship between Gnetales and angiosperms could not be fully ruled out. These results strongly conflict with previously published analyses of mitochondrial data.

Taxon sampling and seed plant phylogeny

We investigated the effects of taxon sampling on phylogenetic inference by exchanging terminals in two sizes of rbcL matrices for seed plants, applying parsimony and bayesian analyses to ten 38‐taxon matrices and ten 80‐taxon matrices. In comparing tree topologies we concentrated on the position of the Gnetales, an important group whose placement has long been disputed. With either method, trees obtained from different taxon samples could be mutually contradictory and even disagree on groups that seemed strongly supported. Adding terminals improved the consistency of results for unweighted parsimony, but not for parsimony with third positions excluded and not for bayesian analysis, particularly when the general time‐reversible model was employed. This suggests that attempting to resolve deep relationships using only a few taxa can lead to spurious conclusions, groupings unlikely to be repeatable with different taxon samplings or larger data sets. The effect of taxon sampling has not generally been recognized, and phylogenetic studies of seed plants have often been based on few taxa. Such insufficient sampling may help explain the variety of phylogenetic hypotheses for seed plants proposed in recent years. We recommend that restricted data sets such as single‐gene subsets of multigene studies should be reanalyzed with alternative selections of terminals to assess topological consistency.

EVOLUTIONARY RELATIONSHIPS IN EPHEDRA (GNETALES), WITH IMPLICATIONS FOR SEED PLANT PHYLOGENY

Evolutionary relationships in Ephedra are difficult to resolve, mainly because there are few informative characters in investigated loci and long distances to outgroups. We address these problems by using a large data set that includes information from seven plastid and nuclear loci and 204 vascular plants. The deepest divergences in Ephedra are weakly supported and differ by analytical method, but they indicate a basal grade of species distributed in the Mediterranean area. New World species are monophyletic, with a South American clade possibly nested within a North American clade. A mainly Asian clade comprises several well‐supported subgroups, of which some are endemic to restricted geographic regions in East or Central Asia; others have a broad distribution that may extend into Europe (E. distachya, E. major) and/or Africa (E. pachyclada–E. somalensis). Ephedra laristanica and E. somalensis are nested within other species, whereas the recognition of E. milleri as a separate species is supported. Our results provide another example of how exceptionally difficult it is to disentangle the early divergences of seed plants. Bayesian analysis strongly supports the “gnetifer” hypothesis, a result rarely found in the literature, but it conflicts with our results from only chloroplast data (“gne‐cup”) and with results of most maximum parsimony analyses (“Gnetales sister”).

Phylogeny of Isoetes (Lycopsida): resolving basal relationships using rbcL sequences

The phylogenetic relationships of Isoetes (Isoetaceae) were investigated by means of a cladistic analysis using plastid rbcL sequences and a representative sample of 18 species. The analysis supports a basal split in Isoetes separating two main groups, one including aquatic species from South America (I. bradei and I. amazonica) and West Africa (I. kersii and I. schweinfurthii), and the other including aquatic, amphibious and terrestrial species representing all major continents. Higher level relationships remain unresolved, but supported groups do conflict with previous morphology-based hypotheses. Comparatively low levels of sequence divergence indicate that the use of more rapidly evolving regions will be required to resolve higher level relationships. The phylogenetically isolated nature of Isoetes will in such analyses make standard outgroup comparisons problematic, and results presented here will in this respect prove important by providing support for choosing among alternative rooting options.

Moonlight pollination in the gymnosperm Ephedra (Gnetales)

Most gymnosperms are wind-pollinated, but some are insect-pollinated, and in Ephedra (Gnetales), both wind pollination and insect pollination occur. Little is, however, known about mechanisms and evolution of pollination syndromes in gymnosperms. Based on four seasons of field studies, we show an unexpected correlation between pollination and the phases of the moon in one of our studied species, Ephedra foeminea. It is pollinated by dipterans and lepidopterans, most of them nocturnal, and its pollination coincides with the full moon of July. This may be adaptive in two ways. Many nocturnal insects navigate using the moon. Further, the spectacular reflection of the full-moonlight in the pollination drops is the only apparent means of nocturnal attraction of insects in these plants. In the sympatric but wind-pollinated Ephedra distachya, pollination is not correlated to the full moon but occurs at approximately the same dates every year. The lunar correlation has probably been lost in most species of Ephedra subsequent an evolutionary shift to wind pollination in the clade. When the services of insects are no longer needed for successful pollination, the adaptive value of correlating pollination with the full moon is lost, and conceivably also the trait.

Micromorphology of the Seed Envelope of Ephedra L. (Gnetales) and Its Relevance for the Timing of Evolutionary Events

Micromorphology of the seed envelope of Ephedra (Gnetales) is known to be variable, but variation patterns have never been systematically documented. We test the usefulness of this feature for species determination and subclade delimitation in Ephedra and investigate the relationship of this character to infrageneric evolutionary patterns. Most species have a basically smooth seed envelope, which in some species appears slightly striate or reticulate due to convex or depressed outer periclinal cell walls. Ephedra rhytidosperma from China and Ephedra torreyana from North America have transverse lamellae formed by the epidermis. A papillate surface is found in respective close relatives of these two species. Micromorphology of the seed envelope is generally not useful for species identification or subclade delineation. The amount of variation is low, and intraspecific variation, which in some cases seems to be correlated with hybridization and/or introgression, complicates species recognition. Furthermore, parallel evolution of similar micromorphological patterns in unrelated subclades of Ephedra is evident and cannot be explained by similar seed dispersal mechanisms. The Asian species with transverse lamellae or papillae on the seed are dispersed by frugivores whereas similar American species are anemochoric. Transverse ridges occur in several Early Cretaceous fossil seeds with affinity to Ephedra. However, our results indicate that the resemblance between these fossils and extant taxa with similar features is superficial and convergent. In line with other recent studies, we find that Cretaceous ephedroids are extinct stem relatives to the extant clade.

Disentangling the Phylogeny of Isoetes (Isoetales), Using Nuclear and Plastid Data

Premise of research. The heterosporous lycopsids of Isoetes show limited morphological and genetic variation despite a worldwide distribution and the ancient origin of the lineage. Here major relationships within the genus are clarified, using a substantially larger sampling of species than in previous studies. A first assessment of divergence times of clades is made, and the implications for dispersal mechanisms and biogeographic distribution patterns are discussed. Methodology. On the basis of sequences from three gene regions and 109 specimens representing 74 species of Isoetes, phylogeny and node ages were estimated using parsimony and Bayesian inference. Pivotal results. Three rooting approaches (outgroup analysis, midpoint rooting, and clock rooting) coherently resolved a diverse clade containing species from South Africa, India, Australia, and South America (clade A) as sister to remaining Isoetes. Analysis of divergence times of clades yielded a median age of the crown group of 147 million years ago (mya) using a birth-death tree prior and 165 mya using a Yule tree prior. Clade A was dated to 111 or 125 mya, respectively. While the earliest divergences in Isoetes appear readily explained by ancient vicariance, patterns in younger clades are consistent with dispersal processes, sometimes over long distances. Isoetes andicola (Amstutz) L.D. Gómez, once hypothesized to represent a separate lineage and assigned to the genus Stylites, is here included in a phylogenetic study for the first time. It is closely related to some other South American species, despite its peculiar morphology with a dichotomizing stem. Conclusions. Despite limited intrageneric variation at the molecular and morphological levels, node ages as well as species composition (phylogeny) indicate a Mesozoic origin of the extant clade. Biogeographic patterns appear complicated and intriguing but need more research. Tuberculate megaspore ornamentation (sensu Pfeiffer) is ancestral in the genus, as indicated by current knowledge. Other megaspore patterns appear restricted to two subclades.

New insights into the evolutionary history of Gnetum (Gnetales)

Gnetum (Gnetales: Gnetaceae) constitutes an evolutionarily isolated gymnosperm clade, comprising about 40 species that inhabit tropical areas of the world. While its closest living relative, the mo ...

Pollen morphology of Ephedra (Gnetales) and its evolutionary implications

Abstract The Ephedra lineage can be traced at least to the Early Cretaceous. Its characteristically polyplicate pollen is well-represented in the fossil record and is frequently used as an indicator of paleoclimate. However, despite previous efforts, knowledge about variation and evolution of ephedroid pollen traits is poor. Here, we document pollen morphology of nearly all extant species of Ephedra, using a combination of scanning electron microscopy (SEM) and light microscopy (LM), and reconstruct ancestral states of key pollen traits. Our results indicate that the ancestral Ephedra pollen type has numerous plicae interspaced by unbranched pseudosulci, while the derived pollen type has branched pseudosulci and (generally) fewer plicae. The derived type is inferred to have evolved independently twice, once along the North American stem branch and once along the Asian stem branch. Pollen of the ancestral type is common in Mesozoic fossil records, especially from the Early Cretaceous, but it is less commonly reported from the Cenozoic. The earliest documentation of the derived pollen type is from the latest Cretaceous, after which it increases strongly in abundance during the Paleogene. The results of the present study have implications for the age of crown group Ephedra as well as for understanding evolution of pollination syndromes in the genus.