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0Новости систематики высших растений Novitates Systematicae Plantarum Vascularium
2023
54:11-16
ISSN 0568-5443 (print) ISSN 2687-1564 (online)
Populus x cinovskisii (Salicaceae), a new cultivated intersectional hybrid of poplar from Belarus, the Baltic countries and Finland
Populus x cinovskisii (Salicaceae) — новый культивируемый межсекционный гибрид тополя из Беларуси, Прибалтики и Финляндии
V. N. Tikhomirov
Belarusian State University
Faculty of Biology, Botany department
Nezavisimosti Ave., 4, Minsk, 220030, Republic of Belarus
tikhomirov_v_n@list.ru, tikhomvn@bsu.by
https://doi.org/10.31111/novitates/2023.54.08
В. Н. Тихомиров
Белорусский государственный университет Биологический факультет, кафедра ботаники пр. Независимости, 4, Минск, 220030, Республика Беларусь tikhomirov_v_n@list.ru, tikhomvn@bsu.by
Abstract. The morphological features and systematic position of a cultivar known as Populus 'Lettland', widespread in Belarus, the Baltic countries and Finland, are reviewed. This taxon is described here as a new intersectional hybrid, Populus x cinovskisii Val. N. Tikhom.
Keywords: Populus, poplar, Baltic countries, Belarus, Finland, new intersectional hybrid.
Аннотация. Обсуждаются морфологические особенности и систематическое положение широко распространенного в Беларуси, странах Прибалтики и Финляндии культивара, известного под названием Populus 'Lettland'. Этот таксон описан как новый межсекционный гибрид Populus x cinovskisii Val. N. Tikhom.
Ключевые слова: Populus, тополь, Беларусь, Финляндия, Прибалтика, новый межсекционный гибрид.
Introduction
Populus L. is a genus of deciduous flowering plants in the family Salicaceae Mirb., native to most of the Northern Hemisphere. The number of Populus species ranges from 22 to 100, plus hundreds of hybrids, varieties and cultivars (Eckenwalder, 1996, 2010; Fang et al., 1999; Tzvelev, 2001). Poplars form one of the most complicated genera that include many cultivated and adventive plants. This is mainly due to high levels of infraspe-cific variability and spontaneous hybridization within the genus (Nasimovich, Kostina, 2015) which makes it difficult to distinguish hybrids and to establish boundaries between species in this genus (Kostina et al., 2017; Nasimovich, 2020).
Many poplar species hybridize in the wild in areas of overlapping distribution and when introduced taxa grow together in botanical gardens and parks. In addition, poplars are of high economic importance, so almost all species of this genus are involved in active breeding work and many artificially obtained hybrids and cultivars are used in forestry and landscaping. At the same time, cultivars and spontaneous hybrids used in urban landscaping can hybridize with each other as well as with native poplar species, eventually leading to the formation of complex swarms of hybrid nature (Vanden
Broeck et al., 2005; Meirmans et al., 2010; Talbot et al., 2012; Hu et al., 2017).
Hybridization can produce stable combinations of genotypes that prove more resistant than the parent species and can become invasive or potentially invasive plants (Gaskin, 2017). One such potentially invasive cultivar in Belarus is Populus 'Lettland'. It is noteworthy that this taxon, despite being one of the most widespread poplar cultivars in the Baltic countries and Belarus, has not yet been formally designated in botanical nomenclature.
According to R. Cinovskis (1977), this poplar was introduced under the name Populus trichocarpa Torr. et A. Gray ex Hook. to the Skriveri Arboretum (Latvia) in the 1930s, from where it was distributed not only to the Baltic countries, but also to Scandinavia. This cultivar is most likely widespread in Southern Finland, as it is the one depicted under the name Populus trichocarpa in "Suomen puu- ja pensaskasvio" (1992: 148). Populus 'Lettland' was introduced to Belarus in 1951 (Fedoruk, 1985). At present, according to our data, it is one of the most widely cultivated poplars in Belarus. This poplar exhibits rapid growth and high yield potential, which makes it widely used in both afforestation and landscaping. It also has robust vegetative propagation capabilities, which enables it to efficiently colonize a wide range
Поступила в редакцию | Submitted: 17.11.2023 Принята к публикации | Accepted: 25.12.2023
Опубликована онлайн | Published online: 27.12.2023 (Страницы | Pages: e08: 1-6)
of secondary habitats such as overgrown quarries, landfill edges, abandoned farmsteads, etc. Populus 'Lettland' is classified as invasive in Latvia (Evarte-Bundere et al., 2022) and a potentially invasive taxon in Belarus (Cher-naya kniga..., 2020).
There are conflicting data on the taxonomic position of this poplar to date. Cinovskis (1977) pointed out the possible hybrid nature of Populus 'Lettland' and that this hybrid is most often considered a cultivar of P. trichocarpa. A. T. Fedoruk (1985) suggested that the parent species of this hybrid are P. trichocarpa1 and probably P. laurifolia Ledeb. and P. suaveolens Fisch. ex Poit. et A. Vilm. N. N. Tzvelev (2012) considered Populus 'Lettland' close to P. x generosa A. Henry (P. deltoides W. Bartram ex Marshall s. l. x P. trichocarpa). A. K. Skvortsov (2010) considered this taxon as a clone of P. tristis Fisch.
Material and methods
This study is based on herbarium specimens, examined by traditional morphological methods. A set of morphological characters, including leaves on long and short shoots, petioles, buds, male and female flowers, was used for taxonomic separation and identification of Populus taxa (Cinovskis, 1977; Fang et al., 1999; Tzvelev, 2001; Eckenwalder, 2010; Skvortsov, 2010).
In 2002-2023, herbarium collections of poplars deposited in V. L. Komarov Botanical Institute of the Russian Academy of Sciences, Saint-Petersburg (LE), M. V. Lomonosov Moscow State University (MW), N. V. Tsitsin Main Botanical Garden of the Russian Academy of Sciences, Moscow (MHA), M. G. Kholodny Institute of Botany of the National Academy of Sciences of Ukraine, Kiev (KW), W. Szafer Institute of Botany of the Polish Academy of Sciences, Kraków (KRAM), Jagiellonian University, Kraków (KRA), V. F. Kupre-vich Institute of Experimental Botany of the National Academy of Sciences of Belarus, Minsk (MSK), and Central Botanical Garden of the National Academy of Sciences of Belarus, Minsk (MSKH), as well as own herbarium collections of about 1000 herbarium voucher sheets deposited in Belarusian State University, Minsk (MSKU) were studied (herbarium codes are cited according to Thiers, 2023).
1 The currently accepted name for this species is P. tristis (Skvortsov, 2008, 2010; POWO, 2023), which I do not agree with. Populus trichocarpa has hairy 3-4-valved capsules, whereas all P. tristis trees I have seen have glabrous, mostly 2-valved capsules. The same was noted by Cinovskis (1977) in Latvian plants. Populus trichocarpa and P. tristis also differ in their appearance. Populus trichocarpa is a large tree up to 75 m tall (Eckenwalder, 2010), whereas P. tristis is a small tree up to 15 m tall.
In addition to herbarium specimens, scanned collections and photographs documenting human observations on online platforms were studied. We used the following resources: Global Biodiversity Information Facility (GBIF, 2023), iNaturalist (2023), Plantarium (2023). Cultivated and escaped plants were also studied throughout Belarus and in southeastern Latvia (Latgale).
Taxonomic decisions are based on protologues and our examination of original material available through online resources (Global Plants on JSTOR, 2023; GBIF, 2023) and follow the latest rules of "International Code of Nomenclature" (ICN) (Turland et al., 2018).
Results
Analysis of the morphological characters of Populus 'Lettland' confirms its proximity to the balsam poplars (Populus sect. Tacamahaca Spach), and the participation of P. trichocarpa in the formation of this hybrid is
obvious (Table). This is clearly indicated by pubescent capsules (a character unique in this group for P. tricho-carpa) and rather dense pubescence of leaf petioles, buds and young shoots. However, our comparison of Populus 'Lettland' with the type material of P. trichocarpa (lec-totype K000592057, epitype2 K000592056 (Belyaeva et al., 2020), isolectotype NY00284002) shows their major difference in leaf morphology. In the P. trichocarpa type material, leaves are broad (length approximately equal to width), with a heart-shaped base and red resin stains on the underside of the leaf blade. In Populus 'Lettland', leaves are much narrower (about 1.5 times as long as wide), with a cuneate base and without resin stains on the underside of the leaf blade.
A detailed study of Populus 'Lettland' leaf morphology indicates the participation of some species of P. sect. Aigeiros Duby in the origin of this hybrid. This is indicated by petiolar characters, which are conservative in poplars (Klimov, Proshkin, 2018; Proshkin, Klimov, 2019, 2020): in Populus 'Lettland' the petioles are distally slightly flattened at right angle to plane of blade, with a weak groove on the adaxial side (Fig.: C), whereas in sect. Tacamahaca the petioles are cylindrical or distally slightly flattened in plane of blade, with
2 I am not sure of the correctness of the epitype designation in this case, as the lectotype is a clearly identifiable specimen (a short shoot with mature leaves and a catkin), whereas the epitype, according to the ICN is "a specimen or illustration selected to serve as an interpretative type when the holotype, lectotype, or previously designated neotype, or any original material associated with a validly published name, is demonstrably ambiguous and cannot be critically identified for purposes of the precise application of the name to a taxon" (Turland et al., 2018: Art. 9.9).
Table. Diagnostic characters of Populus x cinovskisii and related species
Trait P. tristis P. trichocarpa P. x cinovskisii P. x berolinensis
Tree height, m 7-10(15) 30-50(75) to 30 to 30
Crown Spreading Usually roughly conical Broadly ovate Broadly conical
Branchlets Reddish brown, round Reddish brown, becoming grey by third year, round Light brown, angled Yellowish grey, angled
Petiole Cylindrical or distally Cylindrical or distally Distally slightly Distally flattened at
slightly flattened in plane slightly flattened in plane flattened at right angle right angle to plane of
of blade, with a prominent of blade, with a prominent to plane of blade, with blade, with almost no
groove on the adaxial side groove on the adaxial side a weak groove on the adaxial side groove on the adaxial side
Leaf blade shape Usually triangular-ovate to Usually triangular-ovate Oval, ovate or oblong- Ovate or rhombic-
cordate, base cordate or narrowly ovate to ovate, base cuneate to ovate, base broadly
cordate, base rounded to rounded cuneate or rounded
cordate
Leaf blade Abaxial surface white to Abaxial surface white to Abaxial surface greyish Abaxial surface green or
colour greyish white or greenish greyish white or greenish white without red resin slightly white without
white with abundant red white with abundant stains, adaxial surface red resin stains, adaxial
resin stains, adaxial surface red resin stains, adaxial dark green surface green
dark green surface dark green
Leaf margins Not translucent Not translucent Translucent border weakly developed (not along the entire length of the margin and not on all leaves) Translucent
Capsules Glabrous, 2-valved Densely hairy to glabrate, 3- or 4-valved Hairy, 2- or 3-valved Glabrous, 2-valved
a prominent groove on the adaxial side. A weakly developed translucent leaf margin can be observed on some leaves, which is also one of the specific features of species in section Aigeiros. In contrast to typical balsam poplars, resin stains are almost never observed on the underside of the leaves of Populus 'Lettland'. All these observations give us grounds to assume that Populus 'Lettland' is an intersectional hybrid (P. nothosect. Tacageiros Dolat. et Ziel. — Seneta et al., 2021), although with a predominance of characters of P. sect. Tacamahaca. From a morphological point of view, the most probable origin of Populus 'Lettland' is spontaneous or intentional hybridization of P. trichocarpa with P. x berolinensis K. Koch (P. nigra L. x P. laurifolia), but this hypothesis should be verified by the use of molecular genetic methods.
The presence of pronounced invasiveness in Populus 'Lettland' and the ambiguity of the systematic position of this cultivar prompt us to give this taxon a scientific name.
Populus x cinovskisii Val. N. Tikhom., nothosp. nova (P. trichocarpa Torr. et A. Gray ex Hook. x ?P. x berolinensis K. Koch).
Tree up to 25 m tall; bark greyish, darker and cracked at the base of the trunk; crown broadly ovate. Branches spreading; branchlets light brown, angled. Buds conical,
resinous; outer scales pubescent. Leaves: petiole distally slightly flattened at right angle to plane of blade, with a weak groove on the adaxial side (Fig.: C); blade usually ovate or oblong-ovate, 6-12 x 4-7 cm, base cuneate to rounded, basilaminar glands 2, round, translucent border weakly developed (not along the entire length of the margin and not on all leaves), apex obtuse to acute, abaxial surface greyish white without red resin stains, sparsely pubescent, adaxial — dark green, glabrous. Capsules ovoid, 5-6 mm, densely hairy, 2- or 3-valved.
H o l o t y p e (Fig.: A, B): Belarus, Minsk Region, Pu-khovichi District, v. Zazerka. Plantings at the memorial to the fallen in the Great Patriotic War. 53.659479° N, 27.783781° E, 23 V 2004, Val. N. Tikhomirov, A. N. Sen-nikov (MSKU-49014 (sheet 1), MSKU-49015 (sheet 2); isotype — LE 01262744).
Paratypes. Belarus. Minsk Region: Minsk District, vicinity of railway station Zelenoe, mossy pine forest, overgrown ditch, 3 VI 2001, Val. N. Tikhomirov, № 00240 (MSKU); Minsk, 42 Kizhevatova Street, planting along the road, 5 IX 2002, idem, № 01607 (MSKU); ibidem, 58 Kizhevatova Street, 150 m north of the building of the emergency hospital, 5 IX 2002, idem, № 01608 (MSKU); Mogilev Region: Mstislavl city, Yurchenko Street, square near the city library, 24 VIII 2001, idem, № 00802 (MSKU). Estonia. Saare County: Parsamaa, dendraariumis, 18 VII 1959, H. Re-bassoo, A. Paivel (TU265778); Jarva County: Viljandi r.,
Fig. Populus x cinovskisii.
A, B — holotype: A — sheet 1, branch with short shoots and capsules (MSKU-49014); B — sheet 2, coppice shoot (MSKU-49015). C — cross section of petiole taken from a tree growing near the Belarusian State University building, at 7 Kurchatova Street, Minsk.
Vôhmast loodes, Muriku kula, Rôugu park (looduskaitse all), 2 VII 1965, A. Saare, S. Talts (TAA 0097398). Finland. Aland: Jomala, Godby, Hotel Godby, in the garden, 13 VI 1988, Pent-ti Alanko, № 62130 (H1591932); Uusimaa: Helsinki, Torp-parinmaki, Kotitorpantie 2, 3 trees planted in 1982 (probably from Tolppolan taimisto, Vihti), c. 3 m tall, 29 V 1986, Teuvo Ahti, № 44797 (H1565074).
Etymology. The species is named in honour of Raimonds Cinovskis (1930-1998), prominent Latvian botanist, dendrologist, founder and Head of the Dendrology Laboratory of the National Botanical Garden of Latvia.
Acknowledgements
The author thanks Dr. A. N. Sennikov (V. L. Ko-marov Botanical Institute of the Russian Academy of Sciences; Botanical Museum of the Finnish Museum of Natural History) for discussion of the results obtained,
Dr. Keith Chamberlain (Cardiff University, UK) for linguistic corrections and anonymous reviewers and editors for their comments and suggestions.
This work was carried out within the framework of the project B21UZBG-011 funded by the Belarusian Republican Foundation for Fundamental Research.
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