First nuclear DNA C-values for 18 eudicot families.

BACKGROUND AND AIMS: A key target set at the second Plant Genome Size Workshop, held at the Royal Botanic Gardens, Kew in 2003, was to produce first DNA C-value data for an additional 1 % of angiosperm species, and, within this, to achieve 75 % familial coverage overall (up from approx. 50 %) by 2009. The present study targeted eudicot families for which representation in 2003 (42.5 %) was much lower than monocot (72.8 %) and basal angiosperm (69.0 %) families. METHODS: Flow cytometry or Feulgen microdensitometry were used to estimate nuclear DNA C-values, and chromosome counts were obtained where possible. KEY RESULTS: First nuclear DNA C-values are reported for 20 angiosperm families, including 18 eudicots. This substantially increases familial representation to 55.2 % for angiosperms and 48.5 % for eudicots. CONCLUSIONS: The importance of targeting specific plant families to improve familial nuclear DNA C-value representation is reconfirmed. International collaboration will be increasingly essential to locate and obtain material of unsampled plant families, if the target set by the second Plant Genome Size Workshop is to be met.

Life history evolution and genome size in subtribe Oncidiinae (Orchidaceae).

BACKGROUND AND AIMS: Within Oncidiinae, there are several groups of species that are effectively annuals, and we wished to see if these species had smaller genome sizes than average for the subtribe. METHODS: Fifty-four genome size estimates (50 of which are new) for species in subtribe Oncidiinae (Orchidaceae) were examined for the first time in a phylogenetic context to evaluate hypotheses concerning genome sizes and life history traits. RESULTS AND CONCLUSIONS: Within the limits of still relatively sparse sampling, the species that are effectively annuals do appear to have smaller genome sizes than average. However, the genome sizes of their immediate sister group are also small, indicating that changes in genome size preceded the change in life history traits. Genome sizes and chromosome numbers also do not correlate; some slowly growing species have lower chromosome numbers but large genomes and vice versa. Based on a survey of the literature on orchids, it is also clear that epiphytic species have smaller genome sizes than do terrestrial species, which could be an effect of different water relations or the fact that most terrestrial orchids are geophytic or have distinct growth and dormancy phases.

First nuclear DNA C-values for 28 angiosperm genera.

This paper reports first DNA C-values for 28 angiosperm genera. These include first DNA C-values for 25 families, of which 16 are monocots. Overall familial representation is 47.2 % for angiosperms, but is now much higher for monocots (75 %) and basal angiosperms (73.1 %) than for eudicots (38.7 %). Chromosome counts are reported for 22 taxa, including first records for six genera plus seven species. Unrepresented families will become increasingly enriched for monotypic taxa from obscure locations that are harder to access. Thus, completing familial representation for genome size for angiosperms may prove impossible in any short period, and progress towards this goal will become slower.

Nuclear DNA C-values in 30 species double the familial representation in pteridophytes.

Nuclear DNA C-values and genome size are important biodiversity characters with fundamental biological significance. Yet C-value data for pteridophytes, a diverse group of vascular plants with approx. 9000 extant species, remain scarce. A recent survey by Bennett and Leitch (2001, Annals of Botany 87: 335-345) found that C-values were reported for only 48 pteridophyte species. To improve phylogenetic representation in this group and to check previously reported estimates, C-values for 30 taxa in 17 families were measured using flow cytometry for all but one species. This technique proved generally applicable, but the ease with which C-value data were generated varied greatly between materials. Comparing the new data with those previously published revealed several large discrepancies. After discounting doubtful data, C-values for 62 pteridophyte species remained acceptable for analysis. The present work has increased the number of such species' C-values by 93 %, and more than doubled the number of families represented (from 10 to 21). Analysis shows that pteridophyte C-values vary approx. 450-fold, from 0-16 pg in Selaginella kraussiana to 72.7 pg in Psilotum nudum var. gasa. Superimposing C-value data onto a robust phylogeny of pteridophytes suggests some possible trends in C-value evolution and highlights areas for future work.

First Nuclear DNA C-values for 25 Angiosperm Families.

DNA amount is a widely used biodiversity character. As known DNA C-values represent the global angiosperm flora poorly, better coverage of taxonomic groups is needed, including at the familial level. A workshop, sponsored by Annals of Botany , was held at the Royal Botanic Gardens, Kew in 1997. Its key aim was to identify major gaps in our knowledge of plant DNA C-values and recommend targets for new work to fill them by international collaboration. In 1997 C-values were known for approx. 150 families, meaning there was no estimate for most angiosperm families (approx 68%). The workshop recommended a goal of complete familial representation by 2002, as a main target for angiosperms. Bennett et al . ( Annals of Botany86 : 859-909, 2000) presented a fifth supplementary list of angiosperm C-values from 70 original sources which included first C-values for 691 species. Only 12 (1.7%) of these were first C-values for unrepresented families, so the need to improve familial representation was substantially unmet. We began new work to address this in September 1999, and now report first DNA C-values for 25 angiosperm families. Such targeting seems essential to achieve the goal of familial coverage set by the 1997 workshop within 5 years. 4C values range from 0.67 pg (similar to Arabidopsis thaliana ) in Amoreuxia wrightii (Cochlospermaceae) to 7.49 pg in Deutzia prunifolia (Hydrangeaceae). These data support the view that ancestral angiosperms almost certainly had small genomes (defined as 1C ⩽ 3.5 pg). Chromosome counts are reported for 19 taxa, including first records for three genera plus four species.