Morphological and genetic relationships of Myosotis laxa ssp. baltica and ssp. caespitosa, and typification of M. laxa ssp. baltica
Intraspecific taxonomy of <em>Myosotis laxa</em> has been unclear for a long time. <em>M. laxa</em> ssp. <em>baltica</em> has been treated as a microendemic taxon of the Baltic Sea region, which has evolved in the Aland Islands and has spread northwards; the spread to southeast has been declared doubtful. Morphologically intermediate individuals between <em>M. l</em>. ssp. <em>caespitosa</em> and <em>M. l</em>. ssp. <em>baltica</em> exist; these have sometimes been classified as <em>M. l</em>. ssp. <em>laxa</em>. The aim of this paper is to clarify phylogenetic relationships between subspecies of <em>M. laxa</em> s.l. Here, <em>M. laxa</em> ssp. <em>baltica</em> is lectotypified. We proved that typical <em>M. l</em>. ssp. <em>baltica</em> does occur in the south-eastern Baltic region, namely in Estonia, using herbarium and freshly collected material. A group of plants were identified as typical <em>M. l</em>. ssp. <em>baltica</em>, but many specimens showed intermediate characters between <em>M. laxa</em> ssp. <em>baltica</em> and ssp. <em>caespitosa</em>. The two subspecies could be clearly differentiated neither by morphological characteristics nor by ITS sequences.<em> M. laxa</em> s. l. appeared to be monophyletic according to the ITS phylogeny. We propose that <em>Myosotis laxa</em> ssp. <em>baltica</em> is a coastal ecotype of <em>Myosotis laxa</em>, which has adapted to the fluctuating conditions of coastal habitats. Genetically, it has not yet evolved into a separate species and therefore it would be reasonable to assign it a rank of variety. However, further investigation including wider taxon and geographical sampling is needed to finally clarify the position of all subspecies.