The genus Haloxylon Bunge ex Fenzl of the family Chenopodiaceae (Amaranthaceae s.l.) according to the databases International Plant Names Index (IPNI) and Plants of the World Online (POWO) includes 11 species (Haloxylon ammodendron (C.A.Mey.) Bunge ex Fenzl, H. gracile (Aellen) Hedge, H. griffithii (Moq.) Boiss., H. multiflorum (Moq.) Bunge ex Boiss, H. negevensis (Iljin & Zohary) L.Boulos, H. persicum Bunge, H. salicornicum (Moq.) Bunge ex Boiss., H. schmittianum Pomel, H. scoparium Pomel, H. tamariscifolium (L.) Pau, H. thomsonii Bunge ex Boiss.) occurring from the Mediterranean to Central Asia inclusive (Zhu et al., 2004; Dong et al., 2016).
Many of these species were previously considered to be members of the genus Arthrophytum Schrenk, which, according to IPNI and POWO, currently comprises 8 species (Arthrophytum balchaschense (Iljin) Botsch, A. betpakdalense Korovin & Mironov, A. iliense Iljin, A. korovinii Botsch., A. lehmannianum Bunge, A. longibracteatum Korovin, A. pulvinatum Litv., A. subulifolium Schrenk).
In the flora of Kazakhstan (Goloskokov and Polyakov, 1960; Baitenov, 2001) and Central Asia (Pratov, 1972), there are 3 species of the genus Haloxylon: Haloxylon ammodendron (C.A.Mey.) Bunge, Haloxylon aphyllum (Minkw.) Iljin, Haloxylon persicum Bunge. However, according to recent literature sources, the first 2 species are now combined into one species Haloxylon ammodendron (C.A. Mey.) Bunge ex Fenzl. (https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:941607-1), which reduces, in turn, the number of representatives of the genus growing in Kazakhstan. From our point of view, the association of Haloxylon aphyllum with Haloxylon ammodendron is not quite unambiguous. Additional studies are needed here. Since only Haloxylon aphyllum is widespread in the area under study, we use this species name in the article. In the deserts of Central Asia, Haloxylon ammodendron, Haloxylon aphyllum, and H. persicum play an important role in human life, performing, among other things, a protective function (wind control and sand fixation) (Zhu et al., 2004; Dong et al., 2016). In Kazakhstan, species of the genus Haloxylon are distributed mainly in Turanian deserts, occurring in all southern and south-eastern regions of the republic (Goloskokov and Polyakov, 1960; Pratov, 1972).
The development of molecular genetic methods of analysis, now actively used in systematic studies, leads to numerous changes in the taxonomy of almost all groups of plants. Thus, some genera are divided into several genera, and others, on the contrary, are united into one, or species from one genus are considered by systematists within the scope of another genus, hybrid specimens are identified, etc. (Kechaykin et al., 2020; Sumbembayev et al., 2020; Sumbembayev et al. (Kechaykin et al., 2020; Sumbembayev et al., 2021, 2023a; 2023b; Sukhorukov et al., 2022, 2023a, 2023b; Friesen et al., 2022; Lazkov and Veselova, 2022; Terletskaya et al., 2023; Osmonali et al., 2023 etc.).
Considering that morphologically some representatives of genera Haloxylon, Arthrophytum and Anabasis L., belonging to the same tribe Salsoleae of subfamily Salsoloideae, are very similar at certain stages of their development, the question of determination of their systematic belonging is actual. The present article is devoted to the results of one of such studies.
During expeditionary studies on the flora of the Eastern and Northeastern part of Betpakdala, in particular on the identification of rare and endemic species of this region, we noted a strong similarity between the species Arthrophytum balchaschense and species of the genus Haloxylon (Haloxylon aphyllum). The similar features that attracted our attention include: spatial arrangement of young green shoots, structure of bark, shape of fruits (in the latter case when examined in detail). Therefore, to clarify the systematic affiliation of the plants we were interested in, we collected their samples not only to replenish herbarium collections, but also as material for molecular genetic studies.
To clarify the correct identification of the species as Arthrophytum balchaschense, the collected specimens were compared (checked) with the Type specimen stored at the Institute of Botany and Phytointroduction (AA) under number AA0002446. It was once collected and described by M.G. Popov (Popov, 1936) as Anabasis pauciflora Popov. Almost in the same period, M.M. Ilyin described the species Anabasis balchaschensis Iljin (Ilyin, 1936a, 1936b, 1936c, 1936d), which was renamed Arthrophytum balchaschense (Iljin) Botsch (Botschancev, 1954) by V.P. Bochantsev in 1954 (Goloskokov and Polyakov, 1960). Anabasis pauciflora (Pratov, 1972) was also added to Arthrophytum balchaschense as a synonymy, Type specimens of which were submitted to the V.L. Komarov Botanical Institute in Moscow. V.L. Komarov Botanical Institute in St. Petersburg (LE00054892, LE00054893) (https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:163588-1).
Thus, it was decided to make a molecular genetic analysis and to identify the relatedness of Arthrophytum balchaschense with species of the genus Haloxylon. One of the most important molecular methods in the study of kinship relations at the supra-species (genus) systematic level is the comparison and analysis of aligned DNA sequences of individual fragments of the genome and plastome of plants. In the study of genome fragments (nuclear DNA), nrITS (internal transcribed spacer) analysis of ribosomal DNA is the most popular, while in the plastome a large range of genes and introns is used (Friеsen et al., 2006).