Vol 108, No 12 (2023)

Interspecific hybridization is widespread in plants and is the most important factor in their evolution. For a long time, the main criterion for the hybrid origin of a plant was considered to be the morphological intermediacy of noticeable external characters. However, as the methods of chemistry and molecular biology are introduced into systematics and larger samples are studied, the researches increasingly identify the plants which are chemically and genetically hybrid, but are outwardly indistinguishable from the hypothetical parents or have an unusual combination of traits that does not allow us to recognize the hybridity and the parents by morphology.

Subsequent closer study of such identified “molecular hybrids” with application of morphometry often makes it possible to find morphological, often quantitative or microscopic characteristics which confirm the hybrid nature of these plants as well. Identification and study of cryptic hybrids is important for the systematics of complex taxonomic groups with wide phenotypic plasticity, with a large number of similar species, and simplified morphology. It helps to better understand the conditions under which hybridization can occur, and is important in practical terms, especially for the control of invasive species, for the protection of rare and endangered species, etc.

The phytoplankton in a number of lakes in the Bashkir Trans-Urals (Atavdy, Sultankul (2017), Bursunsy, Kuldybay (2019), Bolshiye Uchaly, Uzunkul (2021)) and Bashkir Pre-Urals (Bolshoy Tolpak, 2022)) was studied. As a result of the study, the taxonomic structure, quantitative characteristics, dominant species, distribution features of main algal groups were reveald, and their ecological and geographical characteristics werre identified. 257 species and intraspecific taxa of algae from 9 divisions were registered in the algal flora. Green algae (33%), cyanoprokaryotes and diatoms (21% each of total species number) show the highest species diversity in the lakes. The algal flora is specific for each lake and has low degree of floristic similarity (0.13–0.57 according to Sørensen coefficients). In the ecological and geographical terms, the algal floras of lake plankton is represented by typical planktonic species, widespread in waterbodies of the globe, indifferent to water salinity, living only in fresh waterbodies and preferring neutral waters. Quantitative indicators of phytoplankton varied in a wide range of values: number of cells from 4.4 to 344 mln cells/L, biomass from 0.23 to 22.97 mg/L. Dominant species in terms of abundance are represented predominantly by cyanoprokaryotes (Snowella lacustris, Aphanocapsa delicatissima, A. incerta, Aphanizomenon flos-aquae, Gloeotrichia echinulata, Merismopedia tenuissima, Pseudanabaena galeata, Planktolyngbya limnetica, Woronichinia compacta, Anathece clathrata, Rhabdoderma lineare), in terms of biomass by green (Oocystis lacustris, O. borgei, O. marssonii, Scenedesmus apiculatus), dinophyte (Peridinium cinctum, Gymnodinium sp., Ceratium furcoides), desmidium algae (Staurodesmus cuspidatus, Cosmarium contractum, C. cucumis) and cyanoprokaryotes (Pseudanabaena galeata, Aphanizomenon flos-aquae, Gloeotrichia echinulata). According to the value of the saprobity index (Pantle – Bucc by number 1.57–2.80), the lake waters correspond to β- and α-mesosaprobic types of waterbodies with III and IV water quality classes (moderately polluted or dirty water).

Light and scanning electron microscopy were used to study the stomatal complexes of Populus mexicana, which has xeromorphic leaf structure. In this poplar, the stomatal complexes are laterocytic and paracytic. The subsidiary cell walls form the peristomatal rim, which rests upon the outer tangential walls of the guard cells. To elucidate the function of the peristomatal rim, we applied modelling using the finite element method. The modelling has shown that the inner and the outer tangential walls of the guard cells bend outward when the stoma is opening. The peristomatal rim hinders the movements of the outer tangential walls of the guard cells. Due to the peristomatal rim, the open stomatal pore sinks deeper into the epidermis. It is narrower and better covered with the outer stomatal ledges, than the one in the stomatal complex without peristomatal rim. The probability of influence of stomatal mechanics in P. mexicana upon water losses during transpiration is under discussion.

The results of comparative embryological study of the two species from the genus Boechera (B. falcata and B. stricta), which are characterized by a sexual mode of reproduction, and the apomictic M4B accession, an ancient natural hybrid of B. stricta × B. retrofracta, are presented. A detailed description of the ovule development of the studied plants is described. A significant similarity of the ovule development has been shown; a general plan of the ovules structure is ortho-campylotropic, bitegmal, medionucellate. The development of the embryo sac in B. falcata and B. stricta corresponds to the monosporic Polygonum type; in the ovules of the M4B accession, an apomictic unreduced female gametophyte is predominantly formed as a result of Taraxacum-type diplospory. However, in this accession apomixis is facultative, since a small amount of the ovules in the ovary forms a reduced embryo sac with participation of meiosis, but unlike B. falcata and B. stricta, after the second meiotic division, a triad of megaspores is formed, of which the chalazal one is functional. In the ovules of the apomictic M4B accession, underdevelopment of the inner integument was often observed, which, apparently, correlates with arrest of the megasporocyte and embryo sac development, since destruction was often observed in ovules with a short inner integument. This abnormality is likely due to the hybrid nature of the M4B accession rather than apomixis. In this accession, the embryo is formed parthenogenetically, but its development requires endosperm, which apparently develops by pseudogamy, only after triple fusion (fertilization of the fused polar nuclei by sperm). In the absence of endosperm, the embryo perishes, and seed development is arrested.

The paper presents data on six lichen species new to Sakhalin Island. Two of them, namely Physconia subpulverulenta and Bacidia elongata, are recorded for the Sakhalin Region for the first time. Mycobilimbia carneoalbida, Mycobilimbia tetramera, Chaenotheca xyloxena, and Pseudoschismatomma rufescens are noted for Sakhalin Island for the first time. Brief information on distribution, ecology, distinctive characters and illustrations are provided for the species.