Extensive interlineage hybridization in the predominantly clonal Hydrilla verticillata.

Premise: The submersed aquatic plant Hydrilla verticillata ("hydrilla") is important ecologically and economically due to its aggressive growth in both indigenous and nonindigenous regions. Substantial morphological variation has been documented in hydrilla, including the existence of monoecious and dioecious "biotypes." Whereas plastid sequence data have been used previously to explore intraspecific diversity, nuclear data have yet to be analyzed in a phylogenetic context.

Through thick and thin: cryptic sympatric speciation in the submersed genus Najas (Hydrocharitaceae).

Cryptic sympatric species arise when reproductive isolation is established in sympatry, leading to genetically divergent lineages that are highly similar morphologically or virtually indistinguishable. Although cryptic sympatric species have been reported in various animals, fungi, and protists, there are few compelling examples for plants. This investigation presents a case for cryptic sympatric speciation in Najas flexilis, a widespread aquatic plant, which extends throughout northern North America and Eurasia.

Phytogeography of Najas gracillima (Hydrocharitaceae) in North America and its cryptic introduction to California.

Premise Of The Study: The discontinuous North American distribution of Najas gracillima has not been explained satisfactorily. Influences of extirpation, nonindigenous introduction, and postglacial migration on its distribution were evaluated using field, fossil, morphological, and molecular data. Najas is a major waterfowl food, and appropriate conservation measures rely on accurate characterization of populations as indigenous or imperiled.

The plastid genome of Najas flexilis: adaptation to submersed environments is accompanied by the complete loss of the NDH complex in an aquatic angiosperm.

The re-colonization of aquatic habitats by angiosperms has presented a difficult challenge to plants whose long evolutionary history primarily reflects adaptations to terrestrial conditions. Many aquatics must complete vital stages of their life cycle on the water surface by means of floating or emergent leaves and flowers. Only a few species, mainly within the order Alismatales, are able to complete all aspects of their life cycle including pollination, entirely underwater.

Extreme conservation of the psaA/psaB intercistronic spacer reveals a translational motif coincident with the evolution of land plants.

Although chloroplast transcriptional and translational mechanisms were derived originally from prokaryote endosymbionts, chloroplasts retain comparatively few genes as a consequence of the overall transfer to the nucleus of functions associated formerly with prokaryotic genomes. Various modifications reflect other evolutionary shifts toward eukaryotic regulation such as posttranscriptional transcript cleavage with individually processed cistrons in operons and gene expression regulated by nuclear-encoded sigma factors. We report a notable exception for the psaA-psaB-rps14 operon of land plant (embryophyte) chloroplasts, where the first two cistrons are separated by a spacer region to which no significant role had been attributed.