Taxonomic revision of the Erigeron acris group (Asteraceae) in Murmansk Region, Russia, reveals a complex pattern of native and alien taxa Author Sennikov, Alexander N. https://orcid.org/0000-0001-6664-7657 Botanical Museum, Finnish Museum of Natural History, University of Helsinki, Helsinki 00014, Finland alexander.sennikov@helsinki.fi Author Kozhin, Mikhail N. https://orcid.org/0000-0002-0153-0287 Avrorin Polar-Alpine Botanical Garden-Institute of Kola Science Centre of the Russian Academy of Sciences, Apatity 184209, Russia text PhytoKeys 2023 2023-11-15 235 83 128 http://dx.doi.org/10.3897/phytokeys.235.111020 journal article http://dx.doi.org/10.3897/phytokeys.235.111020 1314-2003-235-83 DAE8B14D13855B5FAEB8B73D9910F4F7 4. Erigeron x intercalaris Sennikov, sp. hybr. nov. Fig. 7 Type . Russia . Karelian Republic : Louhi District , "Paanajaervi , Rajala, vaegkant vid Maentyjoki" [= northern side of Paanajaervi Lake, roadside between formerly populated places], 22.07.1936 , H. Lindberg ( holotype H 039504) . Description. Stems 30-50 cm tall, branched in the upper third or half, intensely to slightly purple-coloured, evenly covered by numerous hairs 1-2 mm long. Cauline leaves 4-8 under the synflorescence, spaced, gradually decreasing towards the stem top, completely covered by numerous hairs 0.5-1(1.5) mm long on both sides or subglabrous at the base below. Synflorescence with long branches carrying solitary to 2-3 capitula, nearly corymbose at the top, with numerous hairs 0.8-1 mm long. Phyllaries 6-7.5 mm long, purple-coloured completely or in the apical part, abundantly covered by hairs 1-2 mm long. Ray flowers intensely lilac. Pappus greyish-white. Figure 7. Holotype of Erigeron x intercalaris Sennikov (H 039504). Courtesy of the Finnish Museum of Natural History, University of Helsinki. Flowers in July to August, fruits in August. Distribution in Murmansk Region. Tetrino Village, Apatity Town (Fig. 4D ). Global distribution. Expected in the Boreal zone of Fennoscandia and Eastern Europe. Etymology. The species epithet ( intercalaris , Lat.: intercalary) reflects the intermediate morphology of the hybrid between its presumed parents. Nomenclatural note. The type locality has been extensively sampled for Erigeron plants, which were distributed by Lindberg (1944) in his exsiccatae. The material from the Maentyjoki River distributed as Plantae Finlandiae Exsiccatae 1370 is taxonomically heterogeneous: a few plants of E. acris s.str. (H 339936 pro parte) were mixed with abundant collections of its hybrid with E. rigidus (H 339936 pro parte, H 039487, OULU 059260). The latter specimens are paratypes of our E. x intercalaris . The hybrid plants look very slender and depressed, much less vigorous than the specimens of E. acris s.str. collected in the same locality, thus probably indicating outbreeding depression ( Bleeker et al. 2007 ). Taxonomic note. The hybrid differs from E. acris in a regular purple colouration of its stems and phyllaries, and in a shorter and sparser pubescence on its leaves and stems. It differs from E. rigidus in a denser and longer hairiness of its stems, leaves and phyllaries, and in a lesser purple colouration of its stems and phyllaries.