Open access peer-reviewed chapter

Hybridogenic Activity of Invasive Species of Asteraceae

By Maria A. Galkina and Yulia K. Vinogradova

Submitted: November 13th 2019Reviewed: January 27th 2020Published: April 11th 2020

DOI: 10.5772/intechopen.91370

Downloaded: 423


We studied taxa from genus Bidens, Solidago, and Erigeron, sect. Conyza (Asteraceae). By analyzing the nucleotide sequences of the internal transcribed spacer (ITS1)-ITS2 site, the hybrid origin of the Bidens × decipiens, previously attributed to the North American alien species B. connata, was confirmed. The analysis of trnL-trnF sequences showed that the native B. cernua is the maternal species and the invasive B. frondosa is the paternal species in all probabilities. Diagnostic morphological features of the three Solidago taxa growing together in the vicinity of Pskov have been studied: a native S. virgaurea, an invasive species of North American origin S. canadensis, and their hybrid S. × niederederi. S. × niederederi has an intermediate position between S. virgaurea and S. canadensis. The hybrid origin of S. × niederederi is proven by molecular analysis of nuclear DNA nucleotide sequences (ITS1-ITS2 site). It is not yet possible to unambiguously answer the question which parent species is maternal and which is paternal. We also studied invasive species of the genus Erigeron sect. Conyza in the Mediterranean. Occasionally occurring in Southern Europe, individuals of E. canadensis × E. sumatrensis with intermediate morphological features, described as “Conyza × rouyana,” are likely unstable and soon “absorbed” by the parent species E. sumatrensis. Contrary to the hypothesis by C. Elton explaining the success of plant invasion in a new homeland by strengthening hybridization processes in the secondary distribution range.


  • hybrids
  • hybridization
  • invasive species
  • Bidens × decipiens
  • Solidago × niederederi
  • Erigeron canadensis
  • E. sumatrensis
  • ITS1-ITS2 site
  • rpl32-trnL intergenic spacer
  • trnL-trnF intergenic spacer

1. Introduction

There is a hypothesis that the strengthening of hybridization processes in the secondary distribution range contributes to more successful existence of plants in their new homeland [1, 2]. Under unusual conditions, alien species can form hybrids with closely related native species, as well as with other alien plants inhabiting a given area. Often, hybrids are better adapted to secondary distribution range conditions than parent taxa [3, 4, 5], resulting in landscapes in a new home area. Successful recombination of genetic traits of parent species reduces the lag phase (a period of adaptation of an alien taxon to new conditions during which there is not yet active introduction into natural phytocoenosis and expansion of the secondary distribution range) and leads to the formation of new active “species transformers.” Cross-pollinated plant species are the most predisposed to hybridization. Sympatric species are less likely to be cross-species hybridized than allopatric species or populations [6]. The share of hybrid taxa among invasive species of Middle Russia reaches 10% [7].

For a long time, the most important factor in limiting hybridization was geographical isolation, but nowadays closely related taxa come into contact with each other through a multitude of anthropogenic “corridors” [8]. Thus, inter-regional immigration occurs by means of the introduction of plants, which can be frequent and repetitive, and therefore it significantly increases immigration flow [9]. If we consider the situation where conditions for the hybridization of closely related taxa already exist, there may be several possible developments that coexist: (a) New hybrid taxon may appear, and (b) native taxon disappears. During hybridization, genetic assimilation occurs, and new genes are injected into one or both parent species. Hybrids, even being fertile, can, however, be reproductively isolated from parent plants due to the effect of the selection on reproductive traits (allopolyploidy, heterozygous translocations, recombination, mitochondrial DNA-specific differences) and/or due to factors that predetermine crossing (flowering phenology, separation of ecological niches). Interspecific hybridization may also facilitate the naturalization of rare genotypes and cause an increase in their proportion by inverse crossbreeding with alien parent taxa or hybridization between the hybrids themselves. Greater selection advantages for alien alleles should lead to faster replacement of natural alleles through hybridization and slower replacement without hybridization [10]. The period of displacement (substitution) decreases significantly with increasing immigration flow and selective differentiation. Immigration and selection operate in a variety of ways: increasing immigration levels result in the substitution of native species by suppressing them, while increasing selective differentiation in favor of an alien species results in the substitution of an alien species by genetic assimilation without leaving “pure” native species. At moderate and high immigration rates, the loss of native species can be rapid with or without hybridization. Given the high number of species introduced by humans, the loss of native species can increase only as a result of hybridization [11].

Hybridization increases the threat of extinction of many species due to introgression [12, 13]. High degree of introgression is often manifested by wind-pollinated species such as oaks. Hybridization and introgression can lead to a hybrid complex consisting of many hybrids due to a large number of loci. Thus, multiloci seem to increase the number of hybrid types and genetic complexes and accelerate the reduction of “pure” natural species. In addition, the large number of loci essentially reduces the probability of having a “pure” individual of any parent origin [11]. Without introgression, hybrids, being reproductively isolated, can quickly form a new species. With introgression, speciation slows down as inverse crosses with parent lines occur. The impact of hybridization and introgression on the rate of substitution of native species by closely related ones has been addressed by a mathematical model involving a one-loop bipartite inheritance scheme with different levels of cross-species hybridization [11]. Although the model did not take into account vegetatively propagating hybrids, the results showed that the substitution of natural taxa by alien ones could occur very quickly (in less than five generations). According to the results, hybridization and introgression can increase the degree of substitution of native species by non-native ones. Introgression increases species substitution with low immigration, but prevents substitution when an indigenous species has a significant advantage in selection as well as with higher immigration levels. However, as introductions are associated with increased frequency of hybrids, the impact on the indigenous taxon remains high, and the likelihood of extinction increases significantly [11].

It is known that the highest invasive activity is exhibited by species of Asteraceae family [14], so we have focused our attention on representatives of this group of alien species. It is often impossible to say with certainty whether plants with intermediate morphological features are hybrids (between two species of the same genus). This may also be the case for new ecological forms, resulting from microevolution of species. To confirm or disprove the hypothesis about hybrid origin of certain taxon, it is best to use molecular genetic methods.


2. Materials and methods

DNA was extracted from silica gel dried leaves of Bidens, Solidago, and Erigerontaxa according to the method by Rogers and Bendich [15]. The herbarium specimens are stored in the herbarium of the Tsitsin Main Botanical Garden (MHA). Polymerase chain reaction (PCR) was carried out in a DNA Engine Dyad Peltier Thermal Cycler amplifier (Bio-Rad, United States). For the nuclear ribosomal internal transcribed spacer (ITS) 1-2 (ITS1-ITS2), nnc18s10(forward) and c26A(reverse) primers with an annealing temperature of 50°С were used. For the chloroplast loci (rpl32-trnLand trnL-trnFintergenic spacers), primers were used at the annealing temperature from 0.3 to 65°С [16]. For the chloroplast locus rpl32-trnL, we used primers rpl32F(forward) and trnLUAG (reverse), and for the other chloroplast locus trnL-trnF, we used primers c(forward) and f(reverse). Purification of the PCR product for sequencing was carried out in a mixture of ammonium acetate with ethanol. The nucleotide DNA sequences were determined on an automatic sequencer (Syntol). Further processing of the nucleotide sequences was carried out in the BioEdit program. The data were sent to GenBank (2019), in which these nucleotide sequences can be found by the additional numbers assigned to them (Table 1). Phylogenetic trees were constructed using SplitsTree4.

Sample no.Number of ITS/rpl32–trnL/trnL–trnF sequence in GeneBankTaxonDate and place of collection, notes
de_1aМК559763/ – /MK575566Bidens× decipiens
(= “B. connata”)
Russia, Kaluga region, Milyatinsky Reservoir, 2013 54.4914° N, 34.3393° E
de _1bМК559764/ – /MK575567
de _1cМК559765/ – / MK575568
de _1dМК559766/ – /MK575569
de _2aМК559767/ – /MK575570Russia, Kaliningrad region, 2013
54.95° N, 20.49° E
de _2bМК559768/ – /MK575571
de _2cМК559769/ – /MK575572
de _2dМК559770/ – / –
de _3aМК559771/ – /MK575573Russia, Vladimir region, near Tasinsky village, 2014 Formed with dissected lower leaves 55.567° N, 40.172° E
de _3bМК559772/ – / –
de _3cМК559773/ – / MK575574
de _4aМК559774/ – /MK575575Russia, Vladimir region, near Tasinsky village, 2014 Formed with whole lower leaves
55.567° N, 40.172° E
de _4bМК559775/ – /MK575576
fr_5aМК559780/ – /MK575581B. frondosaRussia, Vladimir region, near Tasinsky village, 2014
55.567° N, 40.172° E
fr_5bМК559781/ – /MK575582Russia, Vladimir region, near Tasinsky village, 2018
55.567° N, 40.172° E
fr_5cМК559782/ – /MK575583
cr_6aМК559755/ – /MK575559B. cernuaRussia, Moscow region, near Zvenigorod town, 2014
55.69° N, 36.74° E
cr_6bМК559756/ – /MK575560
t_7МК559754/ – /MK575558B. tripartitaRussia, Vladimir region, near Tasinsky village, 2018
55.567° N, 40.172° E
cr_8aМК559757/ – /MK575561B. cernua
cr_8bМК559758/ – /MK575562
cr_8cМК559759/ – /−
cr_9aМК559760/ – /MK575563Belarus, Dzerzhinsk, 2018
53.693° N, 27.165° E
сr_9bМК559761/ – /MK575564
cr_9cМК559762/ – /MK575565
fr_10aМК559783/ – /MK575584B. frondosa
fr_10bМК559784/ – /MK575585
de _11aМК559776/ – /MK575577B. decipiens(= “B. connata”)
de _11bМК559777/ – /MK575578
de _11cМК559778/ – /MK575579
de _13МК559779/ – /MK575580Russia, Moscow, park near Sviblovo estate, 2018 55.8639° N, 37.6396° E
v_1aMK491849/MK474079/ –Solidago virgaureaRussia, Pskov region, Pskov district, vicinity of Pskov, idle field, 2018
57.80° N, 28.25° E
v_1bMK491850/MK474080/ –
v_1cMK491851/MK474081/ –
n_2aMK491852/MK474082/ –S.× niederederi
n_2bMK491853/MK474083/ –
n_2c– /MK474084/ –
c_3aMK491854/MK474085/ –S. canadensis
c_3bMK491855/MK474086/ –
c_3cMK491856/MK474087/ –
v_4– /MK474088/ –S. virgaureaRussia, Moscow region, Chekhov district, near the village of Chudinovo, idle field, 2018
55.1° N, 37.5° E
c_5aMK491857/MK474090/ –S. canadensis
c_5b– /MK474089/ –
v_6aMK491858/− / –S. virgaureaRussia, Moscow region, “Losiny Ostrov” National Park, Pine forest, 2014
55.89° N, 37.77° E
v_6bMK491859/− / –
3MK397980/− / –Erigeron sumatrensisItaly, Pompeii, 2016
40.7° N, 14.5° E
5aMK397981/− / –Italy, the Island of Ischia, 2016
40.7° N, 13.9° E
5bMK397982/− / –
5cMK397983/− / –
6MK397984/− / –Italy, Herculaneum, 2016
40.8° N, 14.4° E
8aMK397986/− / –E. sumatrensis×
E. canadensis(?)
Italy, Naples, 2016
40.8° N, 14.2° E
8bMK397987/− / –
10aMK397988/− / –Italy, Pompeii, 2016
40.7° N, 14.5° E
10bMK397989/− / –
13aMK397991/− / –E. canadensisItaly, the Island of Ischia, 2016
40.7° N, 13.9° E
13bMK397992/− / –
16MK397985/− / –Portugal, Lisbon, 2017
38.7° N, 9.1° W
18MK397993/− / –Spain, Madrid, park, 2017
40.4° N, 3.7° W
19MK397994/− / –Erigeronsp.
20MK397995/− / –E. canadensis
22MK397990/− / –

Table 1.

Samples of the studied taxa of Asteraceae.

Note: “E. sumatrensis × E. canadensis (?)” – putative hybrids.


3. Bidens× decipiens

Bidens connataMuhl. ex Willd. is a North American species whose natural area extends from Alaska in the north to Mexico in the south [17]. The species has high polymorphism within native area, and several varieties have been described: B. connatavar. ambiversaFassett, var. anomalaFarwell, var. fallax(Warnstorf) Sherff, var. gracilipesFernald, var. inundataFernald, var. petiolata(Nuttall) Farwell, var. pinnata S. Watson, and var. submuticaFassett [18, 19]. In the second half of the twentieth century, American botanists made suggestions about the hybrid nature of B. connatabased on morphological features [20]. This species was indicated as an alien for Europe [21]. However, European plants called “B. connata” are morphologically different from American samples. Their outer leaves are clearly leaf-shaped, well-developed, and 3–6 cm long, with no reedy flowers, and the first real leaves are less narrow and with more pronounced petioles than those of B. connataand fewer denticles on the leaves, and the denticles, in turn, are usually larger and less regularly located [22]. Plants from European populations have been described as B.× decipiensWarnst. in 1895. The typical excrement material collected by Carl Warnstorf is stored in the herbaria of Edinburgh (E), Frankfurt (FR), and Charles University in Prague (PRC) [23]. In Europe, the locations of B.× decipiensare few and far between. A map of the gradual eastward expansion of this species was previously compiled by the authors of this paper [24] and is shown in Figure 1. Previously, we studied morphological features of B.× decipiensin Russia and found that features of this species are intermediate between the North American invasive B. frondosaL. and the native B. cernuaL. B.× decipiensare covered with two types of hairs—duplex, from two cells (as in B. frondosa), and simple multicellular (as in B. cernua). In addition, the seeds of B.× decipiensare quadrilateral and have four axes (as in B. cernua) and are covered with warts (as in B. frondosa). Heads of B.× decipiensare similar in size and shape to heads of B. frondosa, and the leaves are whole, as in B. cernua. On the basis of these data, we hypothesize the hybrid origin of B.× decipiens[25].

Figure 1.

Map of the secondary distribution range ofBidens×decipiens.

Nucleotide sequence analysis shows that not all individuals defined as B.× decipienscan be called hybrids. The point is that in cases of nucleotide substitutions at the ITS1-ITS2 site differentiating B. frondosaand B. cernua, we encounter heterozygosity of samples of B.× decipiens(and, accordingly, ambiguity of reading of the sequence) in many cases, but still not in all (as it should be expected for the hybrid F). At the same time, each of our samples of B.× decipiensis characterized by at least some such ambiguous readings of nucleotides (C or T, A or T, A or C) (Figure 2) in the case of substitutions, which, of course, confirms the hypothesis of the hybrid origin of this taxon. Populations of B.× decipiensfrom different parts of the range differ in the number of substitutions. Thus, samples from the banks of the Milyatinskoye reservoir in the Kaluga region demonstrate in most cases the presence of ambiguous readings in the case of nucleotide substitutions, with the exception of sample de_1a, in which heterozygosity is not observed in all cases of substitutions. It means that this population is a hybrid one. In addition, both parent species grow on the banks of the Milyatinskoye reservoir in close proximity to the population of B.× decipiens, which indirectly supports this view [26]. Probably, the differences in the sample de_1a are due to the presence of introgression, i.e., this sample is a backcross resulting from crossing of B.× decipienswith B. cernua, because ITS1-ITS2 of this sample has a stronger DNA area similar to B. cernuathan others. The same situation is observed with individuals of B.× decipiensfrom Belarus. B.× decipiensspecimens from the Kaliningrad region, by contrast, in most cases show similarities with B. cernuain the case of substitutions rather than heterozygosity, except for sample de_2a. In this case, there are two possible variants—in the first case, we collected samples of backcrosses and see the result of introgression; in the second case, the parent form is another form of B. frondosa, not the widespread B. frondosavar. frondosa.The second variant is less probable. However, other forms of B. frondosahave been recently found [27]. Among plants of B.× decipienscollected in the Vladimir region, two forms distinct on lower leaves—with a dissected sheet plate (samples de_3a, de_3b, and de_3c) and with a whole sheet plate (de_4a, de_4b)—are clearly distinguished. As it turned out, these forms have genetic differences, but samples 4a and 4b are also not identical in the ITS1-ITS2 section sequences. In this case, it is only possible to estimate which form is closer to B. cernuaand which one to B. frondosausing statistical methods. The plant collected on the territory of Sviblovo Estate in Moscow and based on a set of morphological features defined as B.× decipiens, in the section ITS1-ITS2, has a very high similarity with B. cernua. However, in one case this specimen still has heterozygosity in nucleotide substitutions differentiating B. cernuaand B. frondosa, so we cannot say that this specimen is a form of B. cernua; most likely, it is the result of introgressive hybridization (Figure 2). It is possible that in the case of introgressive hybridization, not only B.× decipiens× B. cernuabut also backcrosses are formed (B.× decipiens× B. frondosa). It is interesting that ambiguous readings of a certain nucleotide are also observed for all B. frondosasamples in the same position, but they are not related to nucleotide substitutions in other taxa (Figure 2). It is not excluded that B. frondosaitself is a species of hybrid origin. This is indirectly proved by the high polymorphism of this species in its natural area.

Figure 2.

Fragment of ITS1-ITS2 site of nuclear DNA of various taxa ofBidensgenus. The nucleotides are coded using the International Union of Pure and Applied Chemistry (IUPAC) nomenclature.

Based on the nucleotide sequences of the ITS1-ITS2 site in the SplitsTree program, the dendrogram is built using the UPGMA method (Figure 3). With high probability (with 100% bootstrap support), two clades were separated—sample t_7 (B. tripartita). One clade was separated by species, specimens B. frondosa(fr_5a, fr_5b, fr_5b, fr_10a, fr_10b), and the other clade included all samples of B.× decipiensand B. cernua, indicating a high similarity.

Figure 3.

Dendrogram based on analysis of the ITS region of DNA of variousBidenstaxa with bootstrap support data.

For trnL-trnF site of chloroplast DNA, samples of B.× decipiensand B. cernuahave no differences (this applies to all plants, including those collected in different regions), while B. frondosadiffers from these taxa by six substitutions of one to two nucleotides and deletion of seven nucleotides (Figure 4). B. tripartitahas another deletion (Figure 4), which is absent in other taxa, which once again indirectly confirms its non-participation to the hybrid origin of B.× decipiens. This means that the aboriginal B. cernuais the maternal species and B. frondosais the paternal species.

Figure 4.

Fragment of the trnL-trnF intergenic spacer of chloroplast DNA of various taxa ofBidensgenus. The nucleotides are coded using IUPAC nomenclature.


4. Solidago× niederederi

We have set ourselves the task to study the features of Solidagohybrids in northwest Russia, because in contemporary publications the most numerous references to S.× niederederiare in the northeastern part of Europe and the Pskov region is the closest region of Russia to it. Previously, on the basis of the analysis of the highly variable noncoding chloroplast region rpl32-trnL by Polish botanists, it was found that hybridization between S. canadensisand S. virgaureacan occur in both directions and both species can be both mother and father plants [28]. We aimed to determine the situation with respect to parental taxa in the Pskov populations of these species.

The main difference between the hybrid S.× niederederiand its parents is the structure of shoot systems (mainly the inflorescence structure, Figure 5). In S. canadensisnumerous heads are collected in a compound raceme, and in S.× niederederithe number of heads is smaller and is collected in a compressed compound raceme, whereas in S. virgaureathe number of heads is smaller, and the branches of the compound raceme are so short that the inflorescence is more like a spike.

Figure 5.

Panicles ofSolidago×niederederiand its parental species.

The size of the heads themselves also varies (Figure 6). S.× niederederiheads have an oval shape and occupy an intermediate position in diameter between parental species, 2201 ± 45 μm (mean ± error average) with a maximum spread of 1762 to 2728 μm, while for S. virgaureaand S. canadensis, these values are 3132 ± 30 μm (2874–3548 μm) and 1591 ± 22 μm (1428–1939 μm), respectively [29].

Figure 6.

Parameters of flower heads ofSolidago×niederederiand its parental species: quartiles (first and third), median, maximum, and minimum values are indicated.

With regard to the length of the head, S.× niederederiplants in Pskov cannot be clearly distinguished from S. canadensisdue to the high variability of this indicator in S. canadensis. However, in terms of average head lengths, the hybrid also occupies an intermediate position between parent species (Figure 6). S. canadensisand S.× niederederishoots are pubescent, while S. virgaureashoots are glabrous, glossy, and sometimes reddish. The leaves of S.× niederederiin the middle part of the shoot are linear-lanceolate and dentate along the edge, with three distinct veins (as in S. canadensis), while in the basal part of the shoot large, ovate, with reticulate veins (as in S. virgaurea). To confirm hybrid origin of S. × niederederipopulation in the vicinity of Pskov, nucleotide sequences of nuclear and chloroplast DNA of Pskov individuals (both parent and hybrid species) as well as individuals of parent species from Moscow region were analyzed. The analysis of the ITS1-ITS2 site showed that in all cases of nucleotide substitutions differentiating S. virgaureaand S. canadensis, S.× niederederihas ambiguous readings (Table 2), indicating heterozygosity, which confirms the hybrid origin of individuals from this population. One sample of S. canadensis(c_3c) showed heterozygosity in three cases of nucleotide substitutions out of four, although morphologically this sample did not differ from other individuals of S. canadensis,which indicates the presence of introgressive hybridization within the Solidagogenus. It is likely that this sample is a backcross (result of crossbreeding S.× niederederiwith the parent species S. canadensis).

Sample no.Position in the alignment

Table 2.

ITS1-ITS2 polymorphism for the Solidago× niederederihybrid and parental species.

The nucleotides are coded using IUPAC nomenclature.

The analysis of the rpl32-trnL high-variable intergenic spacer made it impossible to give an unambiguous answer which species is maternal to S.× niederederiand which is paternal. In contrast to the results obtained by A. Plizhko and J. Zalevska-Galosh [30], our samples of S. canadensishave a higher variability of this section of chloroplast DNA. For example, a sample of s_3a from the Pskov region has a DNA fragment that is absent in other plants of S. canadensisnot only in the Pskov region but also near Moscow (242–264 nucleotides, Table 3). The area occupying positions 271–306 in the alignment of our sequences (292–330 for sample c_3a, Table 3) and differentiating parental species in Polish populations [30] may differ not only in S.× niederederibut also in both parental species. The analysis of another noncoding site of chloroplast DNA, trnL-trnF, also failed to answer this question because all the samples examined were identical in this site. Based on the data obtained, we can only assume that hybridization occurs in both directions in the Pskov population, but there is also a possibility that only one species may be maternal and the other paternal, and it is necessary to search for other, more variable sites of chloroplast DNA.

Sample no.Position in the alignment
191242–264271–306 (292–330)739–741 (746–748, 709–714)894 (900, 923)

Table 3.

Polymorphism of the rpl32-trnL region for the Solidago × niederederi hybrid and parental species.

The nucleotides are coded using IUPAC nomenclature.


5. Erigeronsect. Conyza

Earlier we studied in detail morphological differences between species of the genus Erigeronthat grow in Eurasia [30], and they are shown in Table 4.

FeaturesE. canadensisЕ. bonariensisЕ. sumatrensis
Number of heads/generative shoot500–600No more 30less 500
Diameter of heads, mm4.8 ± 0.1 × 2.4 ± 0.16.1 ± 0.1 × 5.2 ± 0.26.6 ± 0.1 × 3.2 ± 0.2
At the base, swollen
Structure of shoot systemsThe main shoot is barely branched off and ends in a compound raceme occupying the upper third of the escapeThe lower lateral deciduous axes of the inflorescence overturn the main shoot axis; the inflorescence covers the upper third of the shootThe lower lateral deciduous inflorescences are shorter than the main axis of the shoot; the diamond-shaped compound raceme is half the length of the generative shoot
Shape of leavesLinear-lanceolate with denticle marginAlmost linear with 3–5 denticlesLanceolate-oval with a serrated margin
Type of pubescenceThe leaves are light green, slightly pubescent, the stem is light green, strongly pubescentThe leaves are gray-green, the pubescent leaves and stems are strongly pubescent with long silvery trichomesThe leaves are dark green, softly pubescent, the stems are grayish with abundant soft pubescence

Table 4.

Diagnostic morphological features of Erigeronspecies.

Previously a hybrid of Erigeron canadensisand E. sumatrensis—Conyza× rouyanaSennen—was described. A typical specimen of this taxon (P04315552), collected by F. Sennen in Catalonia in 1904, is kept in the herbarium of the Museum of Natural History in Paris [P] [7]. Nevertheless, some botanists did not recognize this hybrid and referred C.× royanato E. floribundus[31], which is now treated as synonymous with E. sumatrensis. However, it cannot be excluded that morphological differences in several individuals could have been caused not by hybrid processes but by adverse environmental conditions.

The analysis of the ITS1-ITS2site of 16 samples of Erigeronsect. Conyza(supposed hybrids and parent taxa) confirmed our conclusions about the higher polymorphism of E. sumatrensisthan E. canadensis: ITS1-ITS2sites of E. canadensissamples were identical, while E. sumatrensishas substitutions and ambiguous readings (Table 5). As for the supposed hybrids (samples 8a, 8b, 10a, 10b, and 22), only in one case an ambiguous reading of the nucleotides coincides with the substitution differentiating E. canadensisand E. sumatrensis, which indicates that the hybridization has taken place, but since in other cases the substitutions are identical (Table 5) and the supposed hybrids have no ambiguous readings, most likely, the reason for their morphological differences is the high polymorphism of E. sumatrensistaxon, to which they can be classified.

Sample no.TaxaPosition in the alignment
65, 129, 136, 137, 238, 472/473, 570/57172, 87, 249, 40483, 576/57795114130, 567/568, 568/569211-212242412430461, 584/585469471/472, 530/531, 558/559499/500502/503520/521535/536559/560598-600
8aE. sumatrensis×
E. canadensis(?)

Table 5.

ITS1-ITS2 polymorphism for different taxa of Erigeronsect. Conyzain the Mediterranean.

The nucleotides are coded using IUPAC nomenclature.

Note: “E. sumatrensis × E. canadensis (?)” – putative hybrids.


6. Conclusions

Thus, the obtained data on hybrid activity among the Asteraceae family of invasive species are ambiguous.

Hybrid B.× decipienshas a low polymorphism. B. cernuais the most polymorphic taxon, and we can assume the presence of introgressive hybridization of B.× decipienswith a maternal species. The analysis of ITS1-ITS2 and trnL-trnF sequences showed that B.× decipiensis of hybrid origin and its maternal form is an aboriginal sequence of B. cernuaand the paternal one is probably invasive B. frondosa. It is possible that B.× decipiensin its present form has already appeared by introgression, but no morphological differences between supposed hybrids (Belarusian and Kaluga plants) and supposed backcrosses (plants from Moscow and Kaliningrad region) have been revealed. It should be noted that B. frondosaitself may be of hybrid origin.

In the northwest of Russia, the populations of three taxa of Solidagogenus—an invasive species of North American origin of S. canadensis, an indigenous species of S. virgaurea, and their hybrid S.× niederederi—grow together in the vicinity of the city of Pskov, which was confirmed by the sequence analysis of the ITS1-ITS2 site. Since both parents, especially S. canadensis, are quite polymorphic taxa, it is impossible to answer unambiguously which of the two species is maternal and which is paternal.

In Southern Europe, the hybriogenic activity of representatives of the genus Erigeronis close to zero. The low hybriogenic activity can also be explained by differences in the chromosome set: in E. canadensis2n = 18 and in E. sumatrensis2n = 54 [32].

Our data on the rare occurrence of hybrids in comparison with parental species in the Asteraceae family contradict the hypothesis explaining the success of plant growth in the new homeland by strengthening hybridization processes in the secondary distribution range [1, 2], but this situation may change in the coming decades, so the hybriogenic activity of invasive species requires attention of the scientific community.



This study was carried out with partial support from the Russian Foundation for Basic Research, grant no. 18-04-00411.


Conflict of interest

The authors declare no conflict of interest.

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Maria A. Galkina and Yulia K. Vinogradova (April 11th 2020). Hybridogenic Activity of Invasive Species of Asteraceae, Invasive Species - Introduction Pathways, Economic Impact, and Possible Management Options, Hamadttu El-Shafie, IntechOpen, DOI: 10.5772/intechopen.91370. Available from:

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