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The estimation of nuclear DNA content has been by far the most popular application of flow cytometry in plants. Because flow cytometry measures relative fluorescence intensities of nuclei stained by a DNA fluorochrome, ploidy determination, and estimation of the nuclear DNA content in absolute units both require comparison to a reference standard of known DNA content. This implies that the quality of the results obtained depends on the standard selection and use. Internal standardization, when the nuclei of an unknown sample and the reference standard are isolated, stained, and measured simultaneously, is mandatory for precise measurements. As DNA peaks representing G1/G0 nuclei of the sample and standard appear on the same histogram of fluorescence intensity, the quotient of their position on the fluorescence intensity axis provides the quotient of DNA amounts. For the estimation of DNA amounts in absolute units, a number of well‐established standards are now available to cover the range of known plant genome sizes. Since there are different standards in use, the standard and the genome size assigned to it has always to be reported. When none of the established standards fits, the introduction of a new standard species is needed. For this purpose, the regression line approach or simultaneous analysis of the candidate standard with several established standards should be prioritized. Moreover, the newly selected standard organism has to fulfill a number of requirements: it should be easy to identify and maintain, taxonomically unambiguous, globally available, with known genome size stability, lacking problematic metabolites, suitable for isolation of sufficient amounts of nuclei, and enabling measurements with low coefficients of variation of DNA peaks, hence suitable for the preparation of high quality samples. [ABSTRACT FROM AUTHOR]

Prospero autumnale (Hyacinthaceae) is taxonomically intricate geophyte species complex with a circum-Mediterranean distribution. In contrast to the extraordinary karyological diversity within P. autumnale complex, morphological variation is limited, and thus, reliable taxonomically diagnostic traits are absent. This investigation addresses whether different ploidy levels within cytotype B7 can be distinguished morpho-anatomically. Populations of B7 cytotype from the Balkan Peninsula and Pannonian Basin were examined. Karyological variation was analyzed, and genome size measurements via flow cytometry were taken for selected individuals from each population. Morpho-anatomical analyses were based on 29 anatomical and 25 morphological traits. Multivariate morphometric analyses revealed significant differences between the three ploidy levels, and this may assist in the identification of plant ploidy level. Although the diploids were the most distinct group, some differences were also found between tetraploids and hexaploids. Genome size variation was found within diploids and tetraploids, and some downsizing was observed in hexaploids. This is the first evaluation of morpho-anatomical variation of cytotype B7 in the P. autumnale complex using a multivariate morphometric approach; further taxonomic and evolutionary studies in this taxonomically complex group are needed. [ABSTRACT FROM AUTHOR]

In plants, hybridization between interspecific taxa leading to chromosome doubling seems to happen regularly and may be an important driver of speciation. Allopolyploid species often have morphological traits from both parents, broader ecological niches, and are hypothesized to be more common going northwards. About 20% of all Sphagnum species have been inferred to be allopolyploids. Here we describe the first allotriploid Sphagnum species in the northern hemisphere, using molecular data, Feulgen densitometry, and morphological examination. Our molecular data also supports the finding of the first polyploid species with inter-subgeneric origin between Acutifolia and Subsecunda. Morphological examination further supports this finding. The Acutifolia progenitor is likely the maternal parent of the new species, named S. 3lydiae, and it is probably S. incundum, S. 3arcticum or S. 3olafii. The Subsecunda parent could not be identified based on molecular and morphological characters. The currently known distribution of S. 3lydiae is confined to regions with arctic and subarctic climate and tundra vegetation in northern Russia. [ABSTRACT FROM AUTHOR]