Liverworts are poorly represented in the record of DNA C-values. Data for not more than nine species are reported in the literature. Here we present flowcytometric measurements of genome size for 32 foliose and 11 thallose species from 22 out of 83 families. The main method used in this study was flow cytometry using propidium iodide as the DNA stain. Feulgen densitometrywas applied as a supplementary method but it proved less suitable because the rigid cellwalls of liverwort tissue are resistant to maceration and apparently often inhibit the diffusion of reagents, which results in low estimates of DNA content. The precise or approximate number of chromosomes were counted, where possible. Among the thallose liverworts, the lowest 1C-value was recorded for Marchantia polymorpha (0.293 pg) and the highest for diploid Pellia epiphylla (7.401 pg). Haploid P. epiphylla (1C = 3.803 pg) had the largest genome among the haploid thalloid liverworts. Among the foliose liverworts, Lejeunea cavifolia with a value of 0.211 pg (1C) was ranked the lowest and Mylia taylorii, a haploid with 7.966 pg (1C) and a large amount of dense heterochromatin, concentrated in one big spherical chromocentre, the highest. This 38-fold variation covers the extremes of the whole sample and exceeds the ca 12-fold variation recorded in mosses (0.174–2.160 pg, 1C). This variation is nevertheless low compared to the 2000-fold interspecific variation found in angiosperms. Several instances of intraspecific variation in DNA ploidy (x and 2x) were found – in Radula complanata, Pellia epiphylla and Metzgeria furcata. In Lophocolea heterophylla, accessions differed 3.37-fold in C-value at haploid chromosome number. This points to cryptic taxonomic differentiation and warns against premature statements about ploidy levels based only on DNA measurements. Significant intraspecific intraploidal variation in C-value was also observed in certain instances. In Frullania dilatata, female plants with two large heterochromatic sex-chromosomes have a 1.35-fold higher C-value than male plants with only one sex chromosome. In most other cases of intraspecific variation the role of sex differences remains to be clarified.
The recently described and originally monotypic genus Discheramocephalus Johnson, 2007 from the Solomon Islands is revised. Six new species are described, illustrated and keyed: Discheramocephalus brucei sp. n. (Cameroon), D. elisabethae sp. n. (Cameroon), D. mikaeli sp. n. (Tanzania), D. stewarti sp. n. (Bolivia), D. jarmilae sp. n. (Bolivia), D. minutissimus sp. n. (Indonesia). Adults of D. minutissimus have a body length of about 400-426 µm, which is at the lower limit among non-egg-parasitoid insects. Evidence is provided that an egg size large enough to produce a viable larva is the main factor limiting miniaturisation of female insects. Females and males of egg-parasitoids are able to overcome the 400 µm threshold and reach limits of 180 µm and 130 µm, respectively. Brain size is likely the second most important factor limiting miniaturisation in insects.
Genome size has been suggested as one of the traits associated with invasiveness of plant species. To provide a quantitative insight into the role of this trait, we estimated nuclearDNAcontent in 93 alien species naturalized in the Czech Republic, belonging to 32 families, by using flow cytometry, and compared it with the values reported for non-invading congeneric and confamilial species from the Plant DNA C-values database. Species naturalized in the Czech Republic have significantly smaller genomes than their congeners not known to be naturalized or invasive in any part of the world. This trend is supported at the family level: alien species naturalized in the Czech flora have on average a smaller genome than is the mean value for non-invading confamilials. Moreover, naturalized and non-invading species clearly differed in the frequency of five genome size categories; this difference was mainly due to very small genomes prevailing and intermediate to very large genomes underrepresented in the former group. Our results provide the first quantitative support for association of genome size with invasiveness, based on a large set of alien species across a number of plant families. However, there was no difference in the genome size of invasive species compared to naturalized but non-invasive. This suggests that small genome size provides alien plants with an advantage already at the stage of naturalization and need not be necessarily associated with the final stage of the process, i.e. invasion.
Flow cytometry measurements confirmed the occurrence of Polypodium ×mantoniae (P. interjectum × P. vulgare) at three localities in the eastern part of the Czech Republic (Blansko and Rudice N of Brno and Javoříčko WNW of Olomouc). Nuclear DNA contents (± Sx) were determined for P. vulgare (2C = 29.00 ± 0.32 pg), P. ×mantoniae (2C = 37.18 ± 0.38 pg) and P. interjectum (2C = 45.24 ± 0.31 pg) using a PAS Partec GmbH flow cytometer (PI staining / standard Vicia faba, 2C = 26.9 pg). The relative DNA content ratio was measured in all pairs of taxa (± Sx range), i.e. P. ×mantoniae : P. vulgare = 1.340 ± 0.008; P. interjectum : P. vulgare = 1.681 ± 0.003; P. interjectum : P. ×mantoniae = 1.255 ± 0.008. Six new localities for Polypodium interjectum were found in the region of Moravský Kras (= Moravian Karst, N of Brno). From the PI/DAPI index it can be inferred that the AT/GC ratio (or heterochromatin occurrence) is 1.05× bigger in P. ×mantoniae than in P. vulgare and 1.08× bigger in P. interjectum than in P. vulgare. Anatomical data (number of thick- walled cells in the anulus, spore length and stomata length) of selected specimens and live samples from the Czech Republic were in good agreement with the range of variation of these features published by earlier authors from other European countries. A brief historical survey of the knowledge of P. interjectum in the Czech Republic is included.