Lemnaceae and Orontiaceae Are Phylogenetically and Morphologically Distinct from Araceae.

Duckweeds comprise a distinctive clade of pleustophytic monocots that traditionally has been classified as the family Lemnaceae. However, molecular evidence has called into question their phylogenetic independence, with some authors asserting instead that duckweeds should be reclassified as subfamily Lemnoideae of an expanded family Araceae. Although a close phylogenetic relationship of duckweeds with traditional Araceae has been supported by multiple studies, the taxonomic disposition of duckweeds must be evaluated more critically to promote nomenclatural stability and utility.

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.

Plastid phylogenomics and molecular evolution of Alismatales.

Past phylogenetic studies of the monocot order Alismatales left several higher-order relationships unresolved. We addressed these uncertainties using a nearly complete genus-level sampling of whole plastid genomes (gene sets representing 83 protein-coding and ribosomal genes) from members of the core alismatid families, Tofieldiaceae and additional taxa (Araceae and other angiosperms). Parsimony and likelihood analyses inferred generally highly congruent phylogenetic relationships within the order, and several alternative likelihood partitioning schemes had little impact on patterns of clade support.

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.

Historical biogeography of Haloragaceae: an out-of-Australia hypothesis with multiple intercontinental dispersals.

Haloragaceae are a cosmopolitan plant family with its centre of diversity in Australia. Here, we investigate the historical biogeography of the family and the role of vicariance or dispersal in shaping its current distribution. DNA sequences from ITS, matK and the trnK 5' and trnK 3' introns were obtained for 102 species representing all 8 genera of Haloragaceae for use in Bayesian molecular dating.

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.

Phylogenetic analysis of the internal transcribed spacer (ITS) region in Menyanthaceae using predicted secondary structure.

Sequences of the nuclear internal transcribed spacer (ITS) regions ITS1 and ITS2 have been used widely in molecular phylogenetic studies because of their relatively high variability and facility of amplification. For phylogenetic applications, most researchers use sequence alignments that are based on nucleotide similarity. However, confidence in the alignment often deteriorates at taxonomic levels above genus, due to increasing variability among sequences.

Phylogenetic systematics and character evolution in the angiosperm family Haloragaceae.

The poorly known Haloragaceae R. Br. (Saxifragales) are highly diverse in habit (small trees to submerged aquatics) and labile in floral merosity (2-4), both uncommon among the core eudicots.

Introduction of Glossostigma (Phrymaceae) to North America: a taxonomic and ecological overview.

Field surveys in eastern North America confirm the naturalization of Glossostigma plants at 19 localities in four states: Connecticut, New Jersey, Pennsylvania, and Rhode Island. DNA sequence analysis of individuals from 14 sampled populations identifies these nonindigenous plants as Glossostigma cleistanthum, a species native to Australia and New Zealand. These results correct prior misidentifications of North American plants as G.

Evidence of hybridity in invasive watermilfoil (Myriophyllum) populations.

Invasions of nonindigenous species have caused ecological devastation to natural communities worldwide, yet the biological bases for invasiveness remain poorly understood. Our studies of invasive watermilfoil (Myriophyllum) populations revealed widespread polymorphisms in biparentally inherited nuclear ribosomal DNA sequences, which were not detected in populations of native North American species. Subclones of the polymorphic regions revealed the occurrence of distinct sequences matching those acquired from both nonindigenous and native North American species.

GENETIC CONSEQUENCES OF RARITY IN ASTER FURCATUS (ASTERACEAE), A THREATENED, SELF-INCOMPATIBLE PLANT.

Aster furcatus is a rare, self-incompatible plant with fewer than 50 known populations throughout its range. We verified self-incompatibility in A. furcatus by conducting experimental self- and cross-pollinations and by examining seed set in a small population comprised of a single clonal genet.

BIOCHEMICAL HETEROPHYLLY AND FLAVONOID EVOLUTION IN NORTH AMERICAN POTAMOGETON (POTAMOGETONACEAE).

Morphologically heterophyllous species of Potamogeton also commonly display biochemical heterophylly with respect to flavonoid compounds. Generally, floating leaves contain an assortment of flavonoids, whereas submersed leaves often exhibit reduced flavonoid profiles. In strictly submersed (homophyllous) species, two patterns occur.