JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. The University of Chicago Press is collaborating with JSTOR to digitize, preserve and extend access to International Journal of Plant Sciences.A two-tiered, nested molecular phylogenetic study of panicoid grasses to explore character state transitions between the C 3 and C 4 adaptive syndromes is presented. A broad survey of 92 panicoid species was sampled for the grass-specific insert sequence in the chloroplast RNA polymerase locus (rpoC2), combining published and unpublished sequences. This portion of the study also included an intensive phylogenetic investigation of one clade of seven species that included Steinchisma hians, which is notable for exhibiting intermediacy between the C 3 and C 4 photosynthetic types. Both rpoC2 data and previously published sequences of the F subunit of an NADH-dependent dehydrogenase were analyzed together for this small group. A rigorous phylogenetic investigation of S. hians and 13 other species of Panicoideae included in the broad survey was then performed with sequences of both rpoC2 and the externally transcribed spacer region of the nuclear ribosomal repeat. These 14 species were selected to maximize representation among photosynthetic subtypes. Combined analysis resolved single origins of two photosynthetic subtypes. A reversion of C 4 to C 3 photosynthesis during the evolution of the lineage that includes S. hians is identified. These and other recent results indicate that repeated reversions from C 4 to C 3 have occurred. The C 3 species Panicum laxum has a strongly supported sister group relationship to S. hians (C 3 -C 4 ). The most parsimonious interpretation is that S. hians represents an incipient reversal from C 3 to C 4 photosynthesis, beginning with the capacity to compartmentalize photorespiratory metabolism in the bundle sheath tissue.

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The genome structure and organization of endogenous caulimovirus sequences from dahlia (Dahlia spp), dahlia mosaic virus (DMV)-D10 from three wild species, D. coccinea (D10-DC), D. sherffii (D10-DS) and D. tenuicaulis (D10-DT), were determined and compared to those from cultivated species of dahlia, D. variabilis (DvEPRS). The complete ca. 7-kb dsDNA genomes of D10-DC, D10-DS, and D10-DT had a structure and organization typical of a caulimovirus and shared 89.3 to 96.6% amino acid sequence identity in various open reading frames (ORF) when compared to DvEPRS. The absence of the aphid transmission factor and the truncated coat protein fused with the reverse transcriptase ORF were common among these DMV-D10 isolates from wild Dahlia species.

Two distinct caulimoviruses, Dahlia mosaic virus (DMV) and Dahlia common mosaic virus, and an endogenous plant pararetroviral sequence (DvEPRS) were reported in Dahlia spp. DvEPRS, previously referred to as DMV-D10, was originally identified in the US from the cultivated Dahlia variabilis, and has also been found in New Zealand, Lithuania and Egypt, as well as in wild dahlia species growing in their natural habitats in Mexico. Sequence analysis of three new EPRSs from cultivated dahlias from Lithuania [D10-LT; 7,159 nucleotide level (nt)], New Zealand (D10-NZ, 7,156 nt), and the wild species, Dahlia rupicola, from Mexico (D10-DR, 7,133 nt) is reported in this study. The three EPRSs have the structure and organization typical of a caulimovirus species and showed identities among various open reading frames (ORFs) ranging between 71 and 97 % at the nt when compared to those or the known DvEPRS from the US. Examination of a dataset of seven full-length EPRSs obtained to date from cultivated and wild Dahlia spp. provided clues into genetic diversity of these EPRSs from diverse sources of dahlia. Phylogenetic analyses, mutation frequencies, potential recombination events, selection, and fitness were evaluated as evolutionary evidences for genetic variation. Assessment of all ORFs using phylogenomic and population genetics approaches suggests a wide genetic diversity of EPRSs occurring in dahlias. Phylogenetic analyses show that the EPRSs from various sources form one clade indicating a lack of clustering by geographical origin. Grouping of various EPRSs into two host taxa (cultivated vs. wild) shows little divergence with respect to their origin. Population genetic parameters demonstrate negative selection for all ORFs, with the reverse transcriptase region more variable than other ORFs. Recombination events were found which provide evolutionary evidence for genetic diversity among dahlia-associated EPRSs. This study contributes to an increased understanding of molecular population genetics and evolutionary pathways of these reverse transcribing viral elements.

Dahlia campanulata and D. cuspidata (Asteraceae, Coreopsideae), two new species from the Mexican states of Oaxaca and Hidalgo, respectively, are described and illustrated. Dahlia campanulata is distinguished by its exceptionally large, pendulous, and campanulate flower heads; leaf petioles with enlarged clasping bases that are much thicker than in any other species of Dahlia; and enormous tubers that exceed 0.5 m in length. Dahlia cuspidata is distinguished by its large outer involucral bracts and cuspidate leaflets, particularly at the terminal end of the rachis and those at the ends of the lateral rachillae; the terminal leaflet on mature leaves is often much more rounded (versus elliptic) than the lateral leaflets.Key words: Asteraceae, Coreopsideae, Dahlia, Heliantheae sensu lato, Hidalgo, Mexico, Oaxaca. RESUMENSe describen e ilustran Dahlia campanulata y D. cuspidata (Asteraceae, Coreopsideae), dos nuevas especies de los estados mexicanos de Oaxaca e Hidalgo respectivamente. Dahlia campanulata se distingue porque las cabezuelas de las flores son excepcionalmente grandes, campanuladas y péndulas, las bases de los pecíolos son alargadas y amplexicaules, mucho más gruesas que en cualquier otra especie; los tubérculos son enormes y exceden 0.5 m de largo. Dahlia cuspidata se distingue por sus brácteas involucrales externas grandes y sus folíolos cuspidados, especialmente el que remata el 1 Current address: