Flowering calendar and morphometric features of pollen for some invasive species in the Middle Russia.
Based on the results of the flowering typical for the invasive plants, a flowering calender was made for these species of the Middle Russia. Seventeen types of seeds are described in the article; they are divided into three groups according to the size of the pollen. "Blooming calendar" for the worst alien plants of the Middle Russia has been made on the basis of multiyear phenological observations. It is the complement to the "Pollen calendar", based on the concentration of airborne pollen (pollen can't usually identify as the concrete species). The 17 most widely distributed alien species were under studying: Acer negundo, Fraxinus pennsylvanica, Amelanchier spicata, A. alnifolia, Impatiens parviflora, I. glandulifera, Echinocystis lobata, Reynoutria × bohemica, Erigeron annuus, Chamomilla suaveolens, Symphyotrichum × salignum, S. novae-angliae, Helianthus tuberosus, Cyclachaena xanthiifolia, Ambrosia artemisiifolia, Solidago canadensis, S. gigantea. The descriptions of pollen grains are presented. Morphometric data for the pollen size were identified. The sample for each species consisted of 50 pollen grains. Microphotos of pollen grains which has been made by means of digital microscope Keyence-VHX1000 are presented. The graph of pollen's volume for studying species has been made. "Blooming calendar" has been composed following our phenological observations in 2015 and herbarium data for the Middle Russia during 1964-2014. There are two peaks of flowering. The first period comes at the early spring (Acer negundo, Fraxinus pennsylvanica), the second one - at the end of the summer (Asteraceae spp., Reynoutria spp.). Thus, the resettlement of invasive species results to prolongation of period with high concentration of pollen in the air, which is dangerous for allergies. Three groups of pollen grains according to their size has been detected. Small pollen grains (the average length of polar axis 19,8-22,3 µm) were observed in Ambrosia artemisiifolia, Cyclachaena xanthiifolia, Erigeron annuus and Fraxinus pennsylvanica. The average pollen grains (the average length of polar axis 25,0-40,1 µm) is observed for Helianthus tuberosus, Symphyotrichum × salignum, S. novae-angliae, Solidago canadensis, S. gigantea, Chamomilla suaveolens, Reynoutria bohemica, Amelanchier spicata, A. alnifolia, Acer negundo. Only Echinocystis lobata has large pollen grains with average length of polar axis 69,1 µm. None species with the very large pollen (polar axis more than 100 µm) we observed. Clinical experiments for widely distributed alien Asteraceae (Helianthus tuberosus, Symphyotrichum × salignum, S. novae-angliae, Solidago spp., etc.) should be made. It is necessary to determine their ability to cause allergic reactions, because their pollen has echinate exine, similar with closely related species, which already recognized as the source of allergy.