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
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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
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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
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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
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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).
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Received: 12 April 2009 / Revised: 22 February 2011 / Accepted: 3 March 2011 /
Published online: 17 June 2011