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In This Issue |
Soria and Meyer-Berthaud present new information on the architecture of a cladoxylalean plant. The Cladoxylopsida, a group that dominated terrestrial ecosystems around 380 million years ago, were spore-producing, and their fossils exhibit diverse growth forms. The new material the authors describe comprises structurally preserved trunk plus root mantle material of Pietzschia levis from a new late Devonian locality of eastern Tafilait, Anti-Atlas, Morocco. Other known specimens of the genus have come from Saxony, the New Albany Shale of eastern USA, and the Frasnian of Russia. A range of morphological variation is discussed, some interpreted as environmentally induced. Resolving more pieces of the fossil puzzle, their descriptions and comparisons to other taxa will promote re-thinking and re-examination of previously catalogued specimens. (see p. 10)
Molecular hybrid index analysis
Watano et al. build on their previous studies of hybridization between two white pine taxa occurring in the mountains of Japan. Zones of hybridization in pines have been described in earlier works based on a broad range of morphological and anatomical characters, and more recent studies have been significant for demonstrating unidirectional gene flow for both maternal and paternal haplotypes, with a reverse mode of inheritance from that found in angiosperms. A logical extension, their current study relies on biparental nuclear markers, using the molecular hybrid index analysis to measure the proportion of genetic contribution from each parent. This study has important implications for introgression studies in plants because most generalizations have been made in angiosperms. (see p. 65)
Dwarf mistletoes
Nickrent et al. provide an in-depth analysis of phylogenetic relationships in the genus Arceuthobium (dwarf mistletoes; see front cover) based on nuclear and chloroplast DNA sequence data. They give complete coverage for the 42 described species of the genus and sequences for both the nuclear ITS region and the trnT-L-F chloroplast region (unless absent). A new key to the genus is provided that attempts to reconcile the data in hand with concepts of monophyly and the need to be able to identify species in the field. Reviewers found the parsimony and distance analyses meticulously constituted, the data thoroughly interpreted, and the morphological and biogeographical insights comprehensively gleaned from a wide variety of sources. (see p. 125)
Hiding out in the Pleistocene
A paper in this issue contributes to our biogeographical understanding of post-glacial Europe. Many such studies have used perennial or woody species, but Koch and Bernhardt chose to study a weedy annual, Microthlaspi perfoliatum (claspleaf pennycress, Brassicaceae), which occurs in all Mediterranean countries except Egypt, as well as throughout the Middle East and Central Asia and has both polyploid and diploid cytotypes. Using molecular markers from the maternally inherited chloroplast genome and biparentally inherited isozymes, the authors describe distinct glacial refugia for the cytotypes and discuss postglacial colonization patterns. Their study has implications for North America as well, where human activities have carried the long-time fugitive cress. (see p. 115)
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