Evolution of leaf blade anatomy in Allium (Amaryllidaceae) subgenus Amerallium with a focus on the North American species.

PREMISE OF THE STUDY: Reconstructing ancestral states is a useful method to understand the pathway and patterns of character evolution and to test specific hypotheses within a phylogenetic context. Using a phylogenetic hypothesis of the subgenus Amerallium and related subgenera based on molecular data, we reconstructed the evolutionary history of leaf blade anatomical characters and identified those characters that are most congruent with phylogenetic relationships. Furthermore, we used these character histories to investigate the evolution of terete leaves and explore a possible correlation between environment and leaf anatomy in the North American species. METHODS: Sixty-seven North American and Old World species were sampled from all major infrageneric taxa and lineages for transectional leaf anatomy. To provide a phylogenetic framework for interpretation, representatives of Old World Amerallium and related subgenera were added to a published data matrix of North American taxa and ITS, ETS, trnL-F, and rpL32-trnL sequences. KEY RESULTS: Four anatomical characters, namely leaf-blade shape in transection, presence versus absence of palisade mesophyll, distribution and orientation of vascular bundles, and position of laticifer cells, were found to be congruent with phylogenetic relationships and useful diagnostic traits within North American species. Character reconstructions show that terete leaves in North American species evolved from flattened leaves via a possible transition from subterete to terete leaves. Furthermore, terete leaves possess traits that are indicative of possible adaptation to xeric environments. CONCLUSIONS: The findings from this study provide valuable information for understanding the evolution of leaf-blade anatomy in North American Allium species.

Managing diversity: Domestication and gene flow in Stenocereus stellatus Riccob. (Cactaceae) in Mexico.

Microsatellite markers (N = 5) were developed for analysis of genetic variation in 15 populations of the columnar cactus Stenocereus stellatus, managed under traditional agriculture practices in central Mexico. Microsatellite diversity was analyzed within and among populations, between geographic regions, and among population management types to provide detailed insight into historical gene flow rates and population dynamics associated with domestication. Our results corroborate a greater diversity in populations managed by farmers compared with wild ones (H E = 0.64 vs. 0.55), but with regional variation between populations among regions. Although farmers propagated S. stellatus vegetatively in home gardens to diversify their stock, asexual recruitment also occurred naturally in populations where more marginal conditions have limited sexual recruitment, resulting in lower genetic diversity. Therefore, a clear-cut relationship between the occurrence of asexual recruitment and genetic diversity was not evident. Two managed populations adjacent to towns were identified as major sources of gene movement in each sampled region, with significant migration to distant as well as nearby populations. Coupled with the absence of significant bottlenecks, this suggests a mechanism for promoting genetic diversity in managed populations through long distance gene exchange. Cultivation of S. stellatus in close proximity to wild populations has led to complex patterns of genetic variation across the landscape that reflects the interaction of natural and cultural processes. As molecular markers become available for nontraditional crops and novel analysis techniques allow us to detect and evaluate patterns of genetic diversity, genetic studies provide valuable insights into managing crop genetic resources into the future against a backdrop of global change. Traditional agriculture systems play an important role in maintaining genetic diversity for plant species.

Molecular systematics of Allium subgenus Amerallium (Amaryllidaceae) in North America.

PREMISE OF THE STUDY: Early plant taxonomists formed hypotheses about relationships among taxa based on characters such as morphology, anatomy, phytochemistry, ecology, and geography. Modern molecular systematic methods, based on DNA sequence variation, augment early methods and provide an additional line of evidence by which to evaluate taxonomic hypotheses. In North America north of Mexico, wild onions (Allium, Amaryllidaceae) are represented by 84 native species, 81 of which belong to subgenus Amerallium. On the basis of morphology, these species have been divided into eight informal taxonomic "alliances" hypothesized to represent shared evolutionary history among species. The main aim of this research was to test the monophyly of the alliances with molecular phylogenetic methods. METHODS: We sampled 74 Amerallium species north of Mexico and two Mexican endemics and constructed a molecular phylogeny of subgenus Amerallium in North America based on predominantly noncoding sequences from two nuclear ribosomal RNA regions (ITS and ETS) and two plastid regions (trnL-F and rpL32-trnL). KEY RESULTS: Most clades are well supported in analyses of nuclear data and when nuclear and plastid data are combined. However, the plastid data alone did not produce a well-resolved or well-supported tree. Morphological alliances were sometimes congruent with groups recovered in the molecular phylogeny, but strict monophyly was observed in only three of eight alliances. CONCLUSIONS: We propose an infrageneric classification that recognizes two sections in New World Amerallium. Because there is substantial incongruence between morphological and molecular groups, we advocate retaining informal alliances rather than adopting formal subsections until further morphological and molecular analyses can be carried out.