Distribution of cytotypes and seasonal variation in the Odontites vernus group in central Europe Rozšíření cytotypů a sezónní variabilita skupiny Odontites vernus ve střední Evropě Petr K o u t e c k ý, Gabrielle T u l e u, Tereza B a ď u r o v á, Jiří K o š n a r, Milan Š t e c h & Jakub T ě š i t e l * Faculty of Science, University of South Bohemia, Branišovská 31, CZ-370 05 České Budějovice, Czech Republic, e-mail: kouta@prf.jcu.cz, margabyii@gmail.com, bajunka@centrum.cz, jirikosnar@seznam.cz, stech@prf.jcu.cz, jakub.tesitel@centrum.cz *corresponding author Koutecký P., Tuleu G., Baďurová T., Košnar J., Štech M. & Těšitel J. (2012): Distribution of cytotypes and seasonal variation in the Odontites vernus group in central Europe. – Preslia 84: 887–904. Based on differences in chromosome number two cytotypes were reported in the Odontites vernus group in central Europe by earlier studies. These cytotypes were also considered to correspond to two seasonal ecotypes that differ in phenology, morphologyand ecology. In this study, we con- ducted a broad screening of central European populations of the O. vernus group using flow cytometry and morphological analysis of characters underpinning the seasonal variation (number of internodes). We confirmed the existence of a widespread diploid (2n = 2x = 18) with a high but vari- able number of internodes and an early-flowering tetraploid (2n = 4x = 40) with a low number of internodes occurring on fallows or as an agricultural weed. In contrast to previous studies, we dis- covered an additional type, which is a distinctly late-flowering tetraploid (2n = 4x = 40) that has the highest number of internodes of all the three types. These plants were mostly recorded in disturbed places in thermophilous steppic grassland and sporadically also in meadows in moderately warm regions. Thus, the close association between seasonal and cytotypic variation was rejected in favour of a concept of a seasonally undifferentiated diploid type, which is an ecological generalist, and two seasonally and ecologically distinct tetraploid types. The reproductive isolation may be based mainly on incompatibility between the ploidy levels (diploid vs. tetraploid plants) and phenological differentiation in the time of reproduction (early vs. late tetraploids). K e y w o r d s: chromosome, flow cytometry, hemiparasite, phenology, reproductive barrier, sympatry Introduction The genus Odontites Ludw. (Rhinanthoid clade of Orobanchaceae; Bennett & Mathews 2006, Těšitel et al. 2010) is comprised of annual or perennial hemiparasitic herbaceous plants or dwarf-shrubs (Bolliger 1993, 1996). It is most diverse in terms of species and life-forms in the Western-Mediterranean area. In central Europe however, it is represented only by two groups of annual herbaceous plants, the Odontites vernus group and O. luteus (L.) Clairv., the only central-European representative of the O. luteus group. The O. vernus group is one of the most common hemiparasitic plants in central Europe and occurs throughout the region (Hartl 1974, Kubát 2000). It is also by far the most wide- spread group within the genus Odontites as its geographical range extends from the west- ern coast of Europe to the Himalayas and Siberia (Bolliger 1996). As suggested by “group”, it is assumed to represent a taxonomically complicated aggregate of several vari- able microspecies, which are difficult to identify. More taxa at different levels were described and partly accepted in the past (e.g. Schneider 1964, Hartl 1974), but only three Preslia 84: 887–904, 2012 887