Folia Geobot (2012) 47:93–103 DOI 10.1007/s12224-011-9103-z Chromosome Numbers and Karyotypes of Species of Vernonia sect. Lepidaploa (Asteraceae: Vernonieae) Vanessa Mancuso de Oliveira & João Semir & Eliana Regina Forni-Martins # Institute of Botany, Academy of Sciences of the Czech Republic 2011 Abstract Vernonia is the largest genus of the tribe Vernonieae (Asteraceae) and comprises more than 1,000 species. In the present study we explore chromosome number and karyotype variation of eight species treated within different subsections of the section Vernonia sect. Lepidaploa. We aimed to explore if these data support the recognition of a single large genus (sensu Baker) or favor its splitting into 22 small genera (sensu Robinson). The species were collected in “cerrado”, rupicolous and disturbed areas in the states of São Paulo and Minas Gerais, Brazil. Chromosome numbers varied from 2n=32 to 60. Most chromosomes were small, and the karyotype analysis revealed a predominance of metacentric and some submetacentric chromosomes. The karyotype symmetry in Vernonia was moderate (TF% 32.2 to 45.9), with the most symmetrical karyotype observed in V. rubriramea. The results obtained here did not conclusively support any of the taxonomic proposals for Vernonia due to the absence of distinctive or characteristic karyotype patterns for any of the taxonomic groupings, i.e., sections and subsections (sensu Baker) or new genera (sensu Robinson). Nevertheless, a tenuous relationship was observed between the chromosome numbers reported in the literature, those recorded here, and the taxonomic alterations suggested by Robinson for the genera Lessingianthus, Chrysolaena, and Vernonanthura that were originally part of Vernonia sensu Baker. Keywords Cytotaxonomy . Idiograms . Mitosis V. M. de Oliveira Programa de Pós-graduação em Biologia Vegetal, Departamento de Botânica, Instituto de Biologia, Universidade Estadual de Campinas (UNICAMP), CP 6109, 13083-970 Campinas, SP, Brazil e-mail: vmancuso@terra.com.br J. Semir : E. R. Forni-Martins (*) Departamento de Biologia Vegetal, Instituto de Biologia, Universidade Estadual de Campinas (UNICAMP), CP 6109, 130839970 Campinas, SP, Brazil e-mail: elianafm@unicamp.br J. Semir e-mail: jsemir@unicamp.br 94 V.M. de Oliveira et al. Introduction The tribe Vernonieae is distinguishable from other Asteraceae by alternate leaves, discoid capitula, and slender styles with filiform, pilose style branches and pilose upper shafts (Bremer 1994). This tribe was originally established by Cassini (1817) and subsequently underwent several revisions (Lessing 1829, 1831a,b; De Candolle 1836; Bentham 1873a,b). The tribe has pantropical distribution and comprises about 40 genera and 450 species in Brazil (Baker 1873). Robinson (1999) recently proposed that the circumscription of the traditional genera of this tribe should be revised, and suggested splitting Vernonia Schreb. into 22 genera (Bremer 1994; Robinson 1999). Most authors did not, however, accept this treatment. Vernonia sensu Baker comprises more than 1,000 species, forming the core of the tribe Vernonieae. According to the most recent data, there are about 350−400 species in South America, which mostly occur in southeastern Brazil, northern Argentina, Paraguay, and Bolivia (Dematteis and Fernández 2000). Brazil is the largest center of diversity of Vernonia in the New World (Keeley and Jansen 1994). Vernonia is one of the most complex genera of the family Asteraceae (Dematteis and Fernández 1998) due to the extreme diversity of its biological forms (Stutts 1988), which range from small shrubs to large trees. Many authors have investigated the taxonomy of this genus (Cabrera 1944; Jones 1970, 1974, 1979a, 1981; Stutts 1988; Robinson 1999) but their conclusions remain contradictory. Most South American species of Vernonia belong to the section Vernonia sect. Lepidaploa (Cass.) DC. (Baker 1873; Bentham 1873b). According to Dematteis (2002), a variety of chromosome numbers have been reported for species in this section, including x=10 for the subsection Oligocephalae, x=16 for Macrocephalae and Axilliflorae, and x=17 for Paniculatae. Chromosomes of several species of Vernonia sect. Lepidaploa were analyzed and despite their small size, discrete differences in their lengths and morphology were noted (Ruas et al. 1991; Dematteis 1996, 1998, 2002; Dematteis and Fernández 1998, 2000). Karyotype asymmetry varies little among the species, suggesting that only small changes in the karyotype constitution accompanied the diversification of this genus. Similar data were obtained in our previous studies (Oliveira et al. 2007a,b ) in some Brazilian species of Vernonia sect. Lepidaploa. The present study aimed to expand our current knowledge on chromosome number and karyotype variation of Vernonia. We focus here on eight species of this genus, and explore if the karyological variation supports the recognition of a single large genus (sensu Baker), or favors its splitting into several smaller genera (sensu Robinson). Material and Methods Eight species of Vernonia sensu Baker from the section Lepidaploa were studied. The samples were collected in “cerrado” (savanna), “campo rupestre” (open, rocky, altitudinal vegetation), and disturbed areas, in the states of São Paulo and Minas Gerais, Brazil (Table 1). Voucher specimens of all the species are deposited in the herbarium of the Universidade Estadual de Campinas (UEC). The species were identified according to Bentham (1873a) and Baker (1873). Chromosome Numbers and Karyotypes of Vernonia 95 Table 1 Vernonia species analyzed in the present study, with their respective locations (all in Brazil), habitats and voucher information (collector names and collection numbers) Species Location Habitat Voucher V. bardanoides Less. Itirapina, SP C VM Oliveira 84 V. beyrichii Less. Itambé do Mato Dentro, MG C IR Costa 138 V. fruticulosa Mart. ex DC. Joaquim Felício, MG C IR Costa 536 V. linearifolia Less. Joaquim Felício, MG RA ME Mansanares 435 V. platensis (Spreng.) Less. Indaiatuba, SP DA VM Oliveira 85 V. rubriramea Mart. Itambé do Mato Dentro, MG C IR Costa 139 V. scorpioides (Lam.) Pers. São Miguel Arcanjo, SP C AM Corrêa 25 V. simplex Less. Joaquim Felício, MG RA IR Costa 570 Habitat: C – “cerrado”; RA – rupicolous areas; DA – disturbed areas. Location: SP – state of São Paulo, Brazil; MG – state of Minas Gerais, Brazil For mitotic analysis, the root tips of newly geminated seeds were pretreated with 0.002M 8-hydroxyquinoline solution for 5 hrs at 14−15°C; the root tips were then fixed in Farmer’s solution (ethanol and acetic acid mixture, 3 : 1 v/v) for 24 hrs and subsequently transferred to 70% ethanol and stored at 4°C. Cytological preparations were obtained using the Giemsa technique. Chromosome numbers were based on the counts from an average of 20 cells from five different individuals of each species. Chromosome measurements were made using the MicroMeasure version 3.2 computer application (Reeves and Tear 2000); chromosome length and centromere position were measured from an average of 10 cells from different individuals from each species. The nomenclature adopted for the chromosome morphology followed Guerra (1986). Idiograms were prepared by arranging the chromosomes on the basis of their morphology and size according to Dematteis (1998), Dematteis and Fernández (1998), and Oliveira et al. (2007a,b), who had previously described the karyotypes of species of the tribe Vernonieae. The total chromosome length (TCL=∑ of all the chromosome lengths of the haploid complement, Guerra 1988) and karyotype symmetry index (TF%=100 ∑S / ∑L, S being the total sum of short arm lengths and L the total sum of chromosome lengths, Huziwara 1962) were calculated. All observations were made using an Olympus BX51 optical microscope and suitable preparations were photographed with a CCD camera (model Evolution MP Color, Media Cybernetics). Results Four different chromosome numbers were observed in the eight species of Vernonia analyzed: 2n=32, 34, 56 and 60 (Table 2, Fig. 1). In addition to the variation in chromosome numbers, other differences were seen among the karyotype formulas and idiograms of the studied species (see Table 2, Figs. 2 and 3). Chromosome length varied from 0.73 μm in V. scorpioides to 3.5 μm 96 V.M. de Oliveira et al. Table 2 Chromosome number, chromosome length, total chromosome length (TCL), symmetry index (TF%), and karyotype formula of the studied species of Vernonia sect. Lepidaploa Species 2n Variation in chromosome length (μm) TCL TF% Karyotype formula 28.2 44.9 8m(A)+3m(B)+3sm(B)+2sm(C) subsection Axilliflorae Benth. V. fruticulosa 32 1.3–2.5 subsection Macrocephalae Benth. V. bardanoides 32 1.09–1.73 23.5 43.19 3m(B)+8m(C)+2sm(B)+3sm(C) V. linearifolia 32 1.02–2.8 30.1 42.1 6m(A)+4m(B)+1m (C)+2sm (A)+ 1sm(B)+2sm(C) 1.29–3.26 35.9 42.3 9m(A)+3m(B)+2sm(A)+3sm(A)+ 1sm(B) 1.15–2.47 29.2 44.4 8m(B)+6m(C)+2sm(B)+1sm(C) 0.92–2.22 44.9 32.2 12m(A)+6m(B)+4 m(C)+2 sm(A)+ 4sm(B)+2sm(C) subsection Oligocephalae Benth. V. simplex 32 subsection Paniculatae Benth. V. beyrichii 34 subsection Scorpioideae Benth. V. platensis 60 V. rubriramea 32 1.3–3.5 40.0 44.4 13m(A)+1m(B)+1sm(A)+1sm(B) V. scorpioides 56 0.73–1.6 31.0 45.9 9m(B)+12m(C)+4sm(B)+3sm(C) Karyotype formula: A – 2.6 to 3.5 μm, B – 1.6 to 2.5 μm, C – 0.7 to 1.5 μm; m – metacentric, sm – submetacentric in V. rubriramea. The total chromosome length (TCL) varied from 23.5 μm in V. bardanoides to 44.9 μm in V. platensis, the species with 2n=60. The karyotype symmetry index TF% varied from 32.2 in V. platensis to 45.9 in V. scorpioides. All of the species had metacentric and submetacentric chromosomes, with most being metacentric (Table 2, Figs. 2 and 3). Discussion The chromosome numbers in the genus Vernonia have been observed to vary from 2n= 18 to 2n= 160 (Bolkhovsvikh et al. 1969; Moore 1973−1977; Goldblatt 1981−1988; Goldblatt and Johnson 1990−1998), but the most frequent ones are 2n=32 and 34. The chromosome numbers of the Vernonia species examined in the present study (Table 2) agree with previous reports, except for V. bardanoides and V. simplex (both with 2n=32). Jones (1979b) had previously reported 2n= 34 for V. bardanoides; Jones (1982) and Oliveira et al. (2007b) reported 2n =34 for V. simplex, while Ruas et al. (1991) indicated 2n =40. Chromosome counts for V. beyrichi (2n = 34), V. linearifolia (2n = 32), and V. rubriramea (2n = 32) are described here for the first time. Most Brazilian species of Vernonia with chromosome data reported belong to the section Lepidaploa (Ruas et al. 1991; Dematteis 1996, 1998, 2002; Dematteis and Fernández 1998, 2000; Oliveira et al. 2007a,b). Previous reports of chromosome Chromosome Numbers and Karyotypes of Vernonia 97 Fig. 1 Mitotic chromosomes of the studied Vernonia species belonging to the subsections Scorpioideae (a−c), Macrocephalae (d−e), Axilliflorae (f), Oligocephalae (g) and Paniculatae (h). a V. platensis (2n=60); b V. rubriramea (2n=32); c V. scorpioides (2n=56); d V. bardanoides (2n=32); e V. linearifolia (2n=32); f V. fruticulosa (2n=32); g V. simplex (2n=32); h V. beyrichii (2n=34). Bar − 1 μm counts for the species of this section indicated x = 10 for the subsection Oligocephalae, x=16 for Macrocephalae, x=14, 15, 16 for Axilliflorae and x=17 for Paniculatae (Dematteis 2002). The only species of the subsection Axilliflorae sensu Baker studied here (V. fruticulosa) had the chromosome number of 2n=32 (Table 2, Fig. 1). This count agrees with a previous report by Oliveira et al. (2007a), and it is a multiple of 16, the 98 V.M. de Oliveira et al. Fig. 2 Idiograms of Vernonia species belonging to the subsection Scorpioideae. a V. platensis (2n=60); b V. rubriramea (2n=32); c V. scorpioides (2n=56). m − metacentric, sm − submetacentric. Bar − 1 μm most frequent basic chromosome number for this subsection (Dematteis 1998, 2002). Most species belonging to this subsection analyzed for chromosome data have been included in the genus Lepidaploa by Robinson (1999), except V. glabrata Less. (2n=51, ca. 52; Jones 1979b) and V. polyphylla Sch. Bip. ex Baker (2n=64, Ruas et al. 1991, Dematteis 2002), which were placed in the genus Lessingianthus H. Rob. Vernonia bardanoides and V. linearifolia, which show 2n=32 (Table 2, Fig. 1), belong to the subsection Macrocephalae sensu Baker. All species in this subsection have chromosome numbers that are multiples of 16, and they show high frequencies of polyploids (Dematteis 2002). The species V. bardanoides had been previously studied by Jones (1979b), who reported it as having n=17 and 34. Most species in this subsection were placed in the genus Lessingianthus by Robinson (1999). Only one species of the subsection Oligocephalae sensu Baker was studied here (V. simplex); it had the chromosome number 2n=32 (Table 2, Fig. 1). This count disagrees with the most frequent chromosome number for Oligocephalae (x=10) suggested by Dematteis (2002) and with previous reports for this species. Jones (1982) and Oliveira et al. (2007b) recorded 2n=34, while Ruas et al. (1991) found 2n=40 for this taxon. Most species of this subsection for which published Chromosome Numbers and Karyotypes of Vernonia 99 Fig. 3 Idiograms of Vernonia species belonging to the subsections Axilliflorae (a), Macrocephalae (b and c), Oligocephalae (d) and Paniculatae (e). a V. fruticulosa (2n=32); b V. bardanoides (2n=32); c V. linearifolia (2n=32); d V. simplex (2n=32); e V. beyrichii (2n=34). m − metacentric, sm − submetacentric. Bar − 1 μm chromosome data are available were transferred by Robinson (1999) to the genus Chrysolaena H. Rob. except V. mollissima, which has 2n=64 according to Dematteis (1997). Vernonia beyrichii was the only species studied here that belongs to the subsection Paniculatae, having the chromosome number 2n=34 (Table 2, Fig. 1), which is the most frequent number in this group. All species of this subsection were included by Robinson (1999) in the genus Vernonanthura H. Rob. and all these species show chromosome numbers that are multiples of 17. The chromosome numbers of all three species belonging to the subsection Scorpioideae sensu Baker (V. platensis, V. rubriramea, and V. scorpioides) (Table 2, Fig. 1) agree with previous reports for this subsection, which recorded several chromosome numbers, with greater frequencies of 10, 16 and 17 (Dematteis 2002). For V. scorpioides we demonstrated here the chromosome number 2n=56 (Table 2, Fig. 1), as was reported earlier by Jones (1970), although n=17 (Jones 1982), 2n=30 (Huynh 1965), and 2n=66 (Dematteis 1998) have also been reported for this species. The species V. platensis, with 2n=60 (Table 2, Fig. 1), had also been previously 100 V.M. de Oliveira et al. reported by Galiano and Hunziker (1987) and Dematteis (2002), and always with chromosome numbers that were multiples of 10 (n=10, 20, 30 and 2n=20, 40, 50, 60). Robinson (1999) placed all species of Scorpioideae into the genus Crysolaena H. Rob. The chromosome numbers obtained here are still insufficient for a more conclusive general cytotaxonomic discussion of the genus Vernonia sensu Baker. Nevertheless, there appears to be only a very tenuous relation between the chromosome numbers reported in the literature or observed here, and taxonomic alterations suggested by Robinson (1999) for the genera Lessingianthus, Chrysolaena, and Vernonanthura (which were originally part of Vernonia sensu Baker 1873). In addition to the results obtained here for V. bardanoides and V. simplex, other reports in the literature indicate differences in chromosome numbers among populations of the same species. These differences may be due to incorrect chromosome counts (due to the small size of the chromosomes), incorrect species identifications (due to the complexity of this group; see Stace 1989), polyploid species/individuals of intermediate morphology, or due to aneuploidy/dysploidy. Aneuploidy and dysploidy are common phenomena in plants and are the result of the loss or gain of one or a few chromosomes. There is no change in the quantity of genomic DNA in the case of dysploidy, in contrast to aneuploidy (Stebbins 1977). The resulting chromosome number will not be an exact multiple of the basic number of a true diploid, and many plant species (particularly wild varieties) can tolerate the gain or loss of a few chromosomes (Stebbins 1977; Malallah et al. 2001). The New World Vernonieae show greater diversity in chromosome numbers and a higher ratio of polyploid species than Old World species (Jones 1979b; Ruas et al. 1991). Jones (1979b) considered x=17 to be the basic number for the New World species, but other authors have suggested x=9, 10, 14, 15, 16, 17 and 19 (Bernardello 1986; Dematteis and Fernández 1998, 2000). The chromosomal analysis described in the present study indicates that the total chromosome length (TCL) represents the main differences between the species (TCL being 23.5 to 44.9 μm), and that these differences were not always linked to differences in chromosome numbers. Although V. rubriramea had only 2n=32 chromosomes, it had large chromosomes (1.3 to 3.5 μm) and the second greatest TCL (40 μm). The species with the highest chromosome numbers, V. scorpioides (2n=56) and V. platensis (2n=60), showed small TCLs (31 and 44.9 μm, respectively) as these chromosomes were very small (0.73 to 2.2 μm) (Table 2). The range of chromosome lengths observed in the present study was smaller (0.73 to 3.5 μm) than that reported by Oliveira et al. (2007a,b) for 11 other species (0.9 to 4.9 μm), but larger than that reported for five species analyzed by Dematteis and Fernández (2000) (1.43 to 2.08 μm). The chromosome morphology was relatively similar among all the studied species. All species analyzed here had metacentric and submetacentric chromosomes, although in different ratios (Table 2, Figs. 2 and 3). Most species had metacentric chromosomes of type A (from 2.6 to 3.5 μm) and B (intermediate size, from 1.6 to 2.5 μm), while all the submetacentric chromosomes were of type B (Table 2, Figs. 2 and 3). This predominance of metacentric chromosomes agrees with other reports for the Vernonieae (Ruas et al. 1991; Dematteis 1996, 1997, 1998; Dematteis and Fernández 1998, 2000; Oliveira et al. 2007a,b). Chromosome Numbers and Karyotypes of Vernonia 101 More symmetrical karyotypes are related to higher TF% indices (a maximum of 50%), while lower TF% values indicate asymmetry mainly caused by displacement of the centromere on some of the chromosomes (Lombello and Forni-Martins 1998). According to Stebbins (1977), there is a tendency for karyotype asymmetry in angiosperms. Ruas et al. (1991) observed that karyotype asymmetry in Vernonia is only moderate. The TF% indices in the present study were similar to those reported by Ruas et al. (1991) and by Oliveira et al. (2007a,b), varying from 42.1% to 45.9% (with the exception of V. platensis, whose index was 32.2%). As such, V. platensis could be considered the most derived species studied here, and V. scorpioides the most primitive. According to Ruas et al. (1991), Dematteis (1996, 1998) and Dematteis and Fernández (1998), the more primitive species of Vernonia (x = 10, 17) have larger chromosomes (1.9 to 2 μm) than more derived species (x = 14, 15; 1.3 to 1.4 μm). Our results agree in part with Dematteis and Fernández (1998) and with Stebbins’ theory (1977), as was previously discussed. Vernonia platensis, which would be considered the most derived species according to the karyotype symmetry (Stebbins 1977), had small chromosomes (0.92 to 2.2 μm), even though its basic chromosome number was x = 10. Vernonia simplex (2n= 32, x =16), which would be considered the most primitive species because of its large chromosomes (1.29 to 3.26 μm), did not have a basic chromosome number that was a multiple of 10 or 17. Despite differences in some of the karyotype parameters, the chromosomal data did not conclusively support any of the taxonomic proposals put forward for Vernonia due to the inexistence of distinctive or characteristic karyotype patterns for the proposed taxonomic group (i.e., sections and subsections (sensu Baker) or new genera (sensu Robinson)). The chromosomes of this group are small and their morphological differences are not readily detected by analysis of just one or a few cells of each species, but require comparisons of average values from larger samples. However, the entire set of characters (number, chromosome length, centromeric position) may be useful in characterizing and distinguishing species whose morphology (vegetative and reproductive characters) are otherwise very similar. Acknowledgements V.M.O. was supported by a scholarship from Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) and E.R.F.M. by a research fellowship from Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq). This work was funded by FAPESP (grant no. 04/13165-9). References Baker JG (1873) Compositae I. Vernonieae. In Martius CF, Eichler AG (eds) Flora brasiliensis 6(2). R. Oldenbourg, Lipsiae, Monachii, pp 1–180 Bentham G (1873a) Compositae. In Bentham G, Hooker JD (eds) Genera Plantarum 2. Lovell Reeve, London, pp 163–533 Bentham G (1873b) Notes of the classification history, and geographical distribution of the Compositae. Bot J Linn Soc 13:355–577 Bernardello LM (1986) Números cromosómicos en Asteraceae de Córdoba. 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Cambridge University Press, Cambridge Stutts JG (1988) Taxonomic revision of Vernonia subsect. Chamaedrys (Compositae: Vernonieae). Rhodora 90:37–99 Received: 12 April 2009 / Revised: 22 February 2011 / Accepted: 3 March 2011 / Published online: 17 June 2011