The genus contains 25 species, which are small, herbaceous annuals distributed in ephemeral waters on both hemispheres. chromosome counts. Based on all the evidence presented here, two new subsections within are described: subsection consisting of TSA the temperate species of the section, and subsection including the Mediterranean species of the section. L.; Elatinaceae, Malpighiales) are small, ephemeral, aquatic herbaceous annuals (Fig. 1), or short-lived perennials, inhabiting the muddy surfaces of ephemeral waters (e.g., temporary pools, shores of lakes and ponds, marshes, and rice-fields). These plants have an interrupted but cosmopolitan distribution, showing strong preference for temperate regions in middle and high latitudes as well tropical mountain ranges (e.g., the Andes). The small, inconspicuous, and mostly cleistogamous flowers of waterworts are usually self-pollinating, but outcrossing can also take place (i.e., facultative autogamy). Since no recent monograph exists for this genus, the total number of species is usually thought to be between 10 (Kubitzki, 2014) to 25 (Tucker, 1986). Most of the species is found in Europe, where ten species is usually registered (Uotila, 2009b) although Flora Europaea lists only eight species (Cook, 1968). Another center of the genus is in North America, where nine species are present (Tucker, 1986). Physique 1 Examples of morphological diversity in the genus (Adanson) Seub. which is represented just by the morphologically distinct (leaves in whorls) species L., and subgenus Seub. (subg. Moesz) which contains all the other species (leaves arranged opposite). The subgenus is usually further divided into two sections: Seub., which includes species with diplostemonous flowers (i.e., stamens arranged in two whorls and thus having double the number of sepals), usually arranged in a tetramerous flower; and (Nutt.) Seub., which includes species of trimerous flowers that show haplostemony (i.e., an arrangement of stamens in a single whorl opposite the sepals thus having an equal quantity of anthers and sepals). While Europe is usually rich in species belonging to section (all species included in this section are native to Europe and temperate Asia with the exception of the North American A. Gray and South American Molau), section has a center of species diversity in North America, while Eurasia boasts just two species, Wight and Schkuhr. The species of waterworts that occur in the Southern Hemisphere are all users of the latter section, with the exception of (Popiela & ?ysko, 2010; Popiela et al., 2011; Popiela et al., 2012; Molnr, Popiela & Lukcs, 2013b; Popiela et al., 2013; Takcs et al., 2013; Kalinka et al., 2014), there TSA are still SMOC1 few studies that deal with this taxonomy of this genus in Europe (Mifsud, 2006; Uotila, 2009c; Molnr et al., 2013a). In the meantime, many new species have been explained from your Americas and Australia (Mason, 1956; Schmidt-Mumm & Bernal, 1995; Albrecht, 2002; Garneau, 2006; L?gaard, 2008). Most researchers agree that seed morphology is usually of outstanding importance in TSA the taxonomy of (Moesz, 1908; Mason, 1956; Cook, 1968; Mifsud, 2006; Molnr et al., 2013a; Molnr et al., 2015), and seed shape (i.e., how much it is curved) as well as seed surface reticulation (i.e., number and shape of seed pits) have traditionally been character types of high significance utilized for recognising species in the genus (Moesz, 1908; Tucker, 1986; Mifsud, 2006; Molnr et al., 2013a). Although vegetative character types, including pedicel length and leaf-shape, are also TSA sometimes emphasised as important sources of taxonomic information (Seubert, 1845; Niedenzu, 1925), these features have generally been thought to be more variable between aquatic and terrestrial forms of the same species than between individual species (Mason, 1956; Molnr et al., 2013a; Molnr, Popiela & Lukcs, 2013b; Molnr et al., 2015). Over recent decades, this genus has received a great deal of attention from molecular phylogenetic workers following the discovery of its important phylogenetic position within Malpighiales (Davis & TSA Chase, 2004). Indeed, the bulk of studies dealing with this order have paid much attention to samples of as representative of the family (Davis et al., 2005; Tokuoka & Tobe, 2006), and only a very recent one focused on internal phylogenetic relationships within the genus (Cai et al., 2016). Many.