Myosotis dubia Arrond. (Boraginaceae), Bleek vergeet-mij-nietje, in Nederland en Duitsland en hoe deze soort te onderscheiden van M. discolor Pers. (Veelkleurig vergeet-mij-nietje)

In 2018, when measuring genome weights of Dutch flora (Zonneveld 2019), we discovered two cytologically different races of Myosotis discolor s.l.: a diploid (0,63 pg / 2C) and a hexaploid (1,78 pg / 2C). The hexaploid plants, without doubt, were M. discolor Pers. The identification of the diploid plants was less certain. They were supposed to represent M. dubia Arrond. Morphological differences between the two forms were hard to get, neither from the literature nor from the plants themselves. We collected 56 plants. From fresh plants we measured genome weight by flow cytometry (Doležel et al. 1989, 1994, Zonneveld 2019). From dried voucher specimens we took morphological measurements. Diploid plants share pure white young corolla lobes, calyx teeth usually up to 50 % of total calyx length, upper leaves alternate, and long patent hairs up to highest leaf of main stem. These plants comply to Myosotis dubia and were found mainly in moist or wet sandy or peaty soil in hayfields or by ditches. Hexaploid plants (Myosotis discolor) share pale yellow young corolla lobes, calyx teeth > 50 % of total calyx length, upper leaves often opposite or nearly so, and long patent hairs absent some distance below highest leaf. These plants were found on dry sandy soil in road verges, meadows and by gardens. Myosotis dubia is new for Germany.