diploidy suggests hybrid origin and sexuality in sorbus subgen. tormaria from thuringia, central...
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ORIGINAL ARTICLE
Diploidy suggests hybrid origin and sexuality in Sorbus subgen.Tormaria from Thuringia, Central Germany
Norbert Meyer • Thomas Gregor • Lenz Meierott •
Juraj Paule
Received: 30 August 2013 / Accepted: 7 March 2014
� Springer-Verlag Wien 2014
Abstract From Thuringia, Central Germany, seven pre-
sumably apomictic microspecies were described within
Sorbus subgen. Tormaria (Sorbus aria 9 torminalis,
S. latifolia group): Sorbus acutiloba, S. acutisecta,
S. decipiens, S. heilingensis, S. isenacensis, S. multicre-
nata, and S. parumlobata. Flow cytometric ploidy estima-
tion revealed one sample-standard ratio class for all taxa
which corresponds to diploidy. As the apomixis in Sorbus
is exclusive to polyploids we deduce that the sampled trees
are F1 or early diploid hybrids of the combination
S. aria 9 torminalis. The oldest name for this combination
is Pyrus 9 decipiens Bechst. 1810 (= Sorbus 9 decipiens
(Bechst.) Petz. & G. Kirchn.). Hence, the wide-spread
presumption that the diploid hybrid Sorbus 9 decipiens is
rare, sterile, and only scarcely found between its parents
does not apply for Thuringia. Here, this taxon forms rela-
tively dense stands and spreads by suckering and fertile
seeds.
Keywords Apomixis � Hybridization � Flow cytometry �Rosaceae � Sorbus
Introduction
The taxonomic complexity within the plant kingdom is
often related to reticulate evolutionary history. Due to the
combination of hybridization, polyploidy, and apomixis,
the genus Sorbus is regarded as one of the taxonomically
most complicated genera in the European flora. In Flora
Europaea (Tutin et al. 1968) there are 104 taxa listed.
However, many new European taxa have been described
since 1968 (e.g. Lepsı et al. 2008; Vıt et al. 2012) and the
majority of them is considered polyploid (for overview of
the British taxa see Pellicer et al. 2012). For Germany,
Buttler and Hand (2008) list 42 species, 32 of them apo-
mictic microspecies.
Early studies suggested that the sexual diploids S. aria,
S. aucuparia, and S. torminalis may be considered ances-
tral taxa for the polyploid lineages (see Pellicer et al.
2012). Cytoembryological and castration experiments
showed that triploid and tetraploid Sorbus taxa are pseu-
dogamous apomicts (Liljefors 1934, 1955). For plants
deriving from crosses between Sorbus subgenus Aria Pers.
and S. subgenus Torminaria (DC.) K. Koch the presence of
pseudogamous apomixis was confirmed by Jankun and
Kovanda (1986, 1987, 1988) and Jankun (1993) using
cytoembryological methods. However, the claim of Jankun
and Kovanda (1988) and Jankun (1993) to have found
apomictic diploids was later rejected (Vıt et al. 2012) and
sexuality in Sorbus is regarded to be exclusively coupled
with diploidy (e.g. Ludwig et al. 2013).
Since the early nineteenth century (Bechstein 1810),
Thuringia in Central Germany has been a focus of taxo-
nomic research in the genus Sorbus. From its Triassic
limestone regions seven endemic taxa of Sorbus subgenus
Tormaria Majovsky & Bernatova (S. aria 9 S. torminalis)
were described between 1810 and 1997: Sorbus acutiloba
N. Meyer (&)
Adlerstraße 6, 90522 Oberasbach, Germany
e-mail: [email protected]
T. Gregor � J. Paule (&)
Department of Botany and Molecular Evolution, Senckenberg
Research Institute and Biodiversity and Climate Research Centre
(BiK-F), Senckenberganlage 25, 60325 Frankfurt am Main,
Germany
e-mail: [email protected]
L. Meierott
Am Happach 43, 97218 Gerbrunn, Germany
123
Plant Syst Evol
DOI 10.1007/s00606-014-1043-7
(Irmisch) Petz. & G. Kirchn., Sorbus acutisecta Reuther &
O. Schwarz, Sorbus decipiens (Bechst.) Petz. & G. Kirchn.,
Sorbus heilingensis Dull, Sorbus isenacensis Reuther,
Sorbus multicrenata Dull, and Sorbus parumlobata
(Irmisch) Petz. & G. Kirchn. (Helmecke and Rode 2010,
2012; nomenclature according to Buttler 2013). These
names are widely accepted by identification books such as
Rothmaler (Jager and Werner 2005), Red Data books
(Fritzlar 2011; Korneck et al. 1996; Schmidt 1998a, b, c, d,
e), or taxonomic standard lists like Euro ? Med PlantBase
(2006–2013).
However, the taxonomic status of these apomictic mi-
crospecies (claimed by Dull 1961; Reuther 1971) is
doubtful. The microspecies mostly build homogeneous
clusters of trees, which may have been generated by
suckering. Furthermore, the specimens of mentioned taxa
are morphologically heterogeneous with a broad variety of
leaf shapes. Only S. isenacensis and S. multicrenata
seemed to be more or less morphologically consistent.
Additionally, isozyme analyses of S. heilingensis are
inconsistent with apomixis as they show just 4 % of iso-
zyme profiles in the offspring identical to parents (Leine-
mann et al. 2010).
The following study is based on the assumption that the
ploidy level in Sorbus is coupled with reproduction mode.
Apomictically fixed microspecies in Sorbus are assumed to
be polyploid, diploid plants are considered sexual (e.g.
Ludwig et al. 2013). In order to assess the reproduction
mode in Thuringian Sorbus taxa and to comment about
their evolutionary origin we combined flow cytometric
ploidy screen with chromosome counts and asked three
main questions: (1) What is the ploidy level in Thuringian
Sorbus taxa? (2) Does the ploidy level correspond with
reproductive system? (3) Could be Thuringian Sorbus taxa
treated as independent microspoecies or morphologically
variable hybrids? (4) Does the current taxonomy reflect the
biological reality and is the conservation status
appropriate?
Materials and methods
Plant material and field work
Eight populations of all seven described Thuringian mi-
crospecies as well as five taxonomically unconfirmed
specimens were collected in summer 2012 (see Fig. 1;
Table 1 for detailed collection history). Additional collec-
tions of Sorbus aria, S. graeca agg., S. torminalis, and
taxonomically unconfirmed specimens from Sorbus sub-
gen. Tormaria from Rhineland-Palatinate were analysed in
order to cover the cytotype variation and to better calibrate
the DNA-ploidy estimations. Prior to analysis, leaves were
preserved in plastic bags and stored at 4 �C for a few days.
For the geographical representation of the collection points
ArcGIS v10.1 (Esri, USA) software with the Esri World
Topographic Map layer was used.
S. acutiloba (syn. S. subcordata): Two trees of identical
leaf shape 15 m apart in the forest area ‘‘Trockene Kehle’’
near Arnstadt matched the type and one of them was col-
lected (T5). All the other observed individuals and homo-
geneous clusters in Arnstadt forest were not only different
from the type but also differed from each other (see para-
graph about taxonomically unconfirmed specimens below,
following S. parumlobata).
S. acutisecta: Ten trees were found at the type locality
on the cliff near farm Probsteizella (part of the village
Frankenroda), all of them unique individuals. Two of them
were collected (T9, T10), as well as four individuals from
the vicinity of the village Wendehausen (T20–23).
S. decipiens: Approximately 45 individuals were found
at the type locality, ten of them were large trees. Specimen
T6 was collected from a homogeneous cluster of trees of
different age on the uphill side of the forest road from the
north end of the location ‘‘Krauterwiese’’ to the hill top of
‘‘Burgberg’’. Specimen T7 was collected from a smaller
group of morphologically identical trees from the downhill
edge of the same forest road. The rest of the population
seemed to consist of unique individuals, out of which four
(T16–19) were collected.
S. heilingensis: There were more than 200 trees of dif-
ferent morphology observed within a large forest area.
Only three specimens growing at the easternmost edge of
the population matched the type selected by Dull (1961),
two of which were collected (T12, T14).
S. isenacensis: Morphologically homogeneous cluster
on the southern slope of the hill ‘‘Horselberg’’ was sampled
(T8).
S. multicrenata: A large homogeneous cluster on the
south slope of ‘‘Greifenstein’’ was sampled (T11).
S. parumlobata: Only one tree at the ‘‘Trockene Kehle’’
in Arnstadt forest closely resembled the type, which was,
however, too high to sample. Kleinz (1999), found three
small trees which approximately fit the type nearby. Leaves
of one of these specimens (T4) were collected.
Taxonomically unconfirmed specimens were collected
in Arnstadt from homogeneous tree clusters at the location
‘‘Wasserleite’’ (T1), the road crossing near ‘‘Trockene
Kehle’’ (T3), and from the upper slope edge facing the
village of Dosdorf (T2). Furthermore, a homogenous
population on the hill ‘‘Katzenstein’’ near Rudolstadt (T13)
and a specimen from the hill ‘‘Fuchsberg’’ in the vicinity of
the village Dorndorf (T15) were sampled. Herbarium
specimens of all analysed Sorbus specimens are stored in
the private herbaria of Lenz Meierott and Norbert Meyer as
well as in Herbarium Senckenbergianum (FR).
N. Meyer et al.
123
Chromosome counts
Chromosomes were counted using the slightly modified
method of Lepsı et al. (2008). Leaf buds were collected on
February 24, 2013 from the trees T5 and T7. After being
stored for couple of days at 4 �C, leaf buds were dissected
and pre-treated with a saturated water solution of 1,4-di-
chlorbenzene for 2–3 h at room temperature and fixed in
ice-cold 3:1 ethanol:acetic acid. Maceration lasted for
1 min in 1:1 ethanol:concentrated HCl at room tempera-
ture. Tissue was subsequently squashed in a drop of aceto-
orcein. Chromosomes were counted using a light micro-
scope Axioskop 2 (Carl Zeiss, Gottingen, Germany) with a
10 9 100 magnification.
Flow cytometry
DNA-ploidy levels were estimated by flow cytometric
analyses of fresh leaf petioles using a Partec CyFlow space
(Partec, Germany) fitted with a high-power UV LED
(365 nm). Leaf petiole tissues of the analysed sample and
internal standard [Glycine max cv. ‘‘Polanka’’ (Dolezel
et al. 1994) or Lycopersicon esculentum cv. Stupicke polnı
tyckove rane (Dolezel et al. 1992)] were co-chopped using
a razor blade in a plastic Petri-dish containing 1 ml of ice-
cold Otto I buffer [0.1 M citric acid, 0.5 % Tween 20; Otto
(1990), Dolezel et al. (2007)]. The suspension was filtered
through Partec CellTrics� 30 lm (Partec, Germany) to
remove tissue debris and incubated for at least 10 min at
room temperature. Isolated nuclei in filtered suspension
were stained with 1 ml of Otto II buffer (0.4 M
Na2HPO4 9 12H2O) containing the AT-specific fluoro-
chrome 40,6-diamidino-2-phenylindole (DAPI; 4 lg ml-1)
and b-mercaptoethanol (2 lg ml-1). The relative fluores-
cence intensity was recorded for 3,000 particles. Sample/
standard ratios were calculated from the means of fluo-
rescence histograms visualised using the FloMax v2.4d
software (Partec, Germany). Only histograms with coeffi-
cients of variation (CVs) \5 % for the G0/G1 peak of the
sample were considered. The sample/standard ratios based
on internal standard L. esculentum were adjusted to those
from G. max using a coefficient based on three repeats of
ratios among the two standards. Delays between harvesting
and flow cytometric measurements did not affect accuracy
or quality of analyses.
Results
Altogether, 30 individuals from 16 Sorbus populations
from Thuringia and Rhineland-Palatinate were investigated
using flow cytometry (see Table 1; Fig. 1). CVs for the G0/
G1 peak of the samples ranged from 0.96 to 2.96 %. Three
distinct classes of sample/standard ratios were identified
with means: 0.55 (±0.010), 0.82 (±0.035), and 1.03
(±0.007). The proportion of the means suggested DNA-
Fig. 1 Geographic origin of the
studied taxa from Thuringia. A
full list of localities is given in
the Table 1
Diploidy suggests hybrid origin and sexuality in Thuringian Sorbus
123
Ta
ble
1C
oll
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on
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tory
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of
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on
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08
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0.5
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tise
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ng
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racl
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stei
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2.8
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86
0�E
0.5
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tise
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racl
iffs
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2.8
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,N
M5
1.1
07
929�N
/10.2
97
95
0�E
0.5
42
x
T-2
0S
.a
cuti
sect
aT
huri
ngia
:E
Wen
deh
ause
n,
south
slope,
bac
km
ost
Kre
uzt
al10.9
.2012
LM
,N
M51.1
56705�N
/10.2
54
23
4�E
0.5
52
x
T-2
1S
.a
cuti
sect
aT
huri
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:W
endeh
ause
n,
south
slope
bac
km
ost
Kre
uzt
al10.9
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LM
,N
M51.1
56156�N
/10.2
55
96
3�E
0.5
52
x
T-2
2S
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sect
aT
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rin
gia
:S
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deh
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n,
sou
thsl
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erg
’’1
0.9
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12
LM
,N
M5
1.1
47
181�N
/10.2
36
09
7�E
0.5
52
x
T-2
3S
.a
cuti
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rin
gia
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deh
ause
n,
sou
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0.9
.20
12
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M5
1.1
46
961�N
/10.2
36
50
6�E
0.5
52
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T-0
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S.
dec
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Th
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ng
ia:
Cas
tle
hil
ln
ear
Wal
ters
hau
sen
22
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012
LM
,N
M5
0.8
88
189�N
/10.5
61
01
9�E
0.5
52
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T-0
7a
S.
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ngia
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astl
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sen,
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slope
22.8
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LM
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M50.8
88146�N
/10.5
61
16
2�E
0.5
52
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T-1
6a
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dec
ipie
ns
Thuri
ngia
:C
astl
ehil
lnea
rW
alte
rshau
sen,
SE
slope
22.8
.2012
LM
,N
M50.8
88308�N
/10.5
60
44
7�E
0.5
52
x
T-1
7a
S.
dec
ipie
ns
Thuri
ngia
:C
astl
ehil
lnea
rW
alte
rshau
sen,
SE
slope
22.8
.2012
LM
,N
M50.8
88029�N
/10.5
61
19
4�E
0.5
42
x
T-1
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S.
dec
ipie
ns
Thuri
ngia
:C
astl
ehil
lnea
rW
alte
rshau
sen,
SE
slope
22.8
.2012
LM
,N
M50.8
88128�N
/10.5
61
17
7�E
0.5
32
x
T-1
9a
S.
dec
ipie
ns
Thuri
ngia
:C
astl
ehil
lnea
rW
alte
rshau
sen,
SE
slope
22.8
.2012
LM
,N
M50.8
89092�N
/10.5
59
88
3�E
0.5
52
x
T-1
2a
S.
hei
lin
gen
sis
Th
uri
ng
ia:
50
0m
No
fH
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nce
of
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05
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59
4�E
0.5
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lin
gen
sis
Th
uri
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uth
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pe
of
‘‘R
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10
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915�N
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22
2�E
0.5
42
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T-0
8a
S.
isen
ace
nsi
sT
hu
rin
gia
:‘‘
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ßer
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rsel
ber
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isen
ach
22
.8.2
012
LM
,N
M5
0.9
53
027�N
/10.4
62
09
4�E
0.5
52
x
T-1
1a
S.
mu
ltic
ren
ata
Th
uri
ng
ia:
Bad
Bla
nk
enbu
rg,
Gre
ifen
stei
nca
stle
21
.8.2
012
KH
50
.68
93
24�N
/11.2
62
83
9�E
0.5
42
x
T-0
4a
S.
pa
rum
lob
ata
Th
uri
ng
ia:
Gro
ße
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ppe
nea
rA
rnst
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,,T
rock
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Keh
le‘‘
22
.8.2
012
LM
,N
M,
KH
50
.80
86
81�N
/10.9
51
07
7�E
0.5
42
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T-0
1S
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bgen
.T
orm
ari
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huri
ngia
:A
rnst
adt,
Was
serl
eite
1.2
km
NW
of
Arn
stad
t-S
iegel
bac
h22.8
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LM
,N
M,
KH
50.8
10221�N
/10.9
43
40
9�E
0.5
42
x
T-0
2S
.su
bgen
.T
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ari
aT
hu
rin
gia
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rnst
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1.4
km
Eo
fA
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Do
sdo
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2.8
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LM
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M,
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50
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89
67�N
/10.9
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21
7�E
0.5
52
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77�N
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06
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0.5
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18
35�N
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86
15
8�E
0.5
52
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f,,F
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sber
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ND
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do
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0.9
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91
550�N
/11.4
51
84
1�E
0.5
42
x
RP
-06
S.
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aR
hin
elan
d-P
alat
inat
e:0.6
km
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esse
nic
h16.6
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TG
,R
H,
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M49.7
16287�N
/6.5
34
69
6�E
0.5
22
x
RP
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S.
ari
aR
hin
elan
d-P
alat
inat
e:0.9
km
NW
Ech
tern
acher
bru
ck1
6.6
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12
TG
,R
H,
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,L
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9.8
20
246�N
/6.4
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43
6�E
0.5
52
x
RP
-07
S.
gra
eca
agg.
Rhin
elan
d-P
alat
inat
e:0.9
km
NW
Ech
tern
acher
bru
ck1
6.6
.20
12
TG
,R
H,
NM
,L
M4
9.8
20
246�N
/6.4
24
43
6�E
14
x
RP
-11
S.
gra
eca
agg
.R
hin
elan
d-P
alat
inat
e:2
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mE
NE
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l1
7.6
.20
12
TG
,R
H,
NM
,L
M4
9.9
41
517�N
/6.6
10
88
0�E
1.0
54
x
RP
-09
S.
sub
gen
.T
orm
ari
aR
hin
elan
d-P
alat
inat
e:0.9
km
NW
Ech
tern
acher
bru
ck1
6.6
.20
12
TG
,R
H,
NM
,L
M4
9.8
20
246�N
/6.4
24
43
6�E
0.8
13
x
RP
-12
S.
sub
gen
.T
orm
ari
aR
hin
elan
d-P
alat
inat
e:2
.1k
mE
NE
Roh
l1
7.6
.20
12
TG
,R
H,
NM
,L
M4
9.9
41
517�N
/6.6
10
88
0�E
0.8
23
x
RP
-04
S.
torm
inali
sR
hin
elan
d-P
alat
inat
e:0.6
km
EM
esse
nic
h16.6
.2012
TG
,R
H,
NM
,L
M49.7
16287�N
/6.5
34
69
6�E
0.5
82
x
Coll
ecto
rs:
T.
Gre
gor
(TG
),R
.H
and
(RH
),K
.H
elm
ecke
(KH
),L
.M
eier
ott
(LM
),N
.M
eyer
(NM
)a
Sp
ecim
enfr
om
type
loca
lity
N. Meyer et al.
123
ploidy levels of 2x:3x:4x or alternatively 4x:6x:8x or
higher. However, several chromosome counts for both T5
and T7 (sample/standard ratio 0.55) revealed 2n = *30,
diploid counts were reported for S. torminalis and S. aria
(e.g. Pellicer et al. 2012) and ploidy levels above 5x have
not yet been reported for the genus Sorbus. According to
Pellicer et al. (2012), genome sizes of the genus Sorbus are
relatively well conserved among different lineages, both in
diploids and polyploids. Hence, we conclude that all the
measured Sorbus subgen. Tormaria specimens from
Thuringia are diploid.
Discussion
All samples of the presumed apomictic Sorbus subgen.
Tormaria taxa from Thuringia were DNA-diploid which
corresponds to 2n = 34 and could be considered F1 or
early hybrids between S. aria 9 S. torminalis. Hybrid
origin is in concordance with previous cpDNA study, in
which most of the studied individuals shared haplotypes
with both presumed parental taxa S. aria and S. torminalis
(Leinemann et al. 2010, 2013). Hybrid origin as well as the
parentage of Sorbus subgen. Tormaria was recently con-
firmed also using the SSR markers (Leinemann et al.
2013). Furthermore, due to exclusive diploidy in studied
samples apomixis can be excluded and the sexuality as
reproductive mode is proposed. Sexuality in Sorbus sub-
gen. Tormaria taxa from Thuringia is in agreement with
previous isozyme study, where only 4 % of isozyme pro-
files in the offspring were identical to parents (Leinemann
et al. 2010) as well as by the observations of the mor-
phologically heterogeneous S. acutiloba and S. heilingensis
trees at collection sites and morphologically heterogeneous
F1 offspring in sowing experiments (Klaus Helmecke
unpublished). Furthermore, a recent SSR analysis of adult
trees and its progeny rejected apomixis but suggested that
genetic structures of adult trees and their natural regener-
ation are the result of clonal propagation (Leinemann et al.
2013). This is in line with Bornmuller (1918), who
observed that Sorbus subgen. Tormaria in Thuringia occurs
in groups of morphologically identical, adjacent individu-
als (i.e. polycormons) and the polycormons deviate from
one another. The combined evidence also further validates
the exclusivity of apomixis for Sorbus polyploids.
One reason for the absence of triploid or tetraploid
specimens of the Sorbus subgen. Tormaria in Thuringia
might be the absence of tetraploid apomictic taxa of the
Sorbus aria group, which are mostly summarized as Sorbus
graeca agg. The occurrence of specimens of Sorbus graeca
agg. seems to be essential for the formation of polyploid
apomictic taxa from the Sorbus subgen. Tormaria as
the polyploid hybrids in Northern Bavaria, Baden-
Wurttemberg, and Rhineland-Palatinate occur either sym-
patric or at least close-by with Sorbus graeca agg. (own
observations).
In this context a fundamental question arises: How could
heterogeneous hybrid populations have been described as
presumably stable taxa? This was probably at least partly a
result of the presence of ample fruiting trees; Irmisch (1856)
and Rose (1868) found the seeds of Thuringian Sorbus
hybrids to be well developed and germinable. Karpati
(1960: 254) defined rules for determination of apomicts and
sexual hybrids: ‘‘If such an intermediate form shows well-
developed and ripe fruit, we can be quite sure without any
further experiments or research that this is a fixed inter-
mediate species. … If however the plant in question only
occurs in one or two specimens here and there and its
specimens do not match morphologically, often also no fruit
is developed or they are dropped undeveloped and unripe,
then we can be convinced that they are primary F1 bas-
tards’’. Interestingly, the lack of fertility is still stressed as a
major characteristic of sexual hybrids within Sorbus by
Kutzelnigg (1995: 333). Further confusion may originate
from different approaches to morphological characters.
While Karpati (1960) demanded a total match of mor-
phology, Dull (1961) was in favour of some morphological
likeness and the ability to produce viable seeds. Accord-
ingly, Dull (1961) included plants into S. heilingensis that
matched the type specimen rather poorly and likewise
Reuther (1971, 1997) with S. acutisecta.
Thuringian members of Sorbus subgen. Tormaria can-
not be treated as independent apomictic microspecies and a
different name should be adopted. Sorbus 9 vagensis
Wilmott 1934 is often used as binomial for diploid S.
aria 9 S. torminalis hybrids (but see Buttler 2004), which
has recently been replaced by the earlier Sorbus 9 tom-
entella Gand. 1875 (see Rich et al. 2010). However, Sor-
bus 9 decipiens (Bechst.) Petz. & G. Kirchn. 1864
(basionym: Pyrus 9 decipiens Bechst. 1810) is older and
should be regarded as the name for this diploid hybrid.
Nevertheless, in Britain, the name Sorbus 9 decipiens is
used in a different sense following Sell (1989). Hence this
British triploid taxon now requires a new name.
Sorbus xdecipiens (Bechst.) Petz. & G. Kirchn., Arbor.
Muscav. [Petzold & Kirchner]: 301. 1864
(Sorbus aria L. x Sorbus torminalis L.)
: Pyrus xdecipiens Bechst., Forstbot.: 236, 614, 1449.
1810
= Sorbus xacutiloba (Irmisch) Petz. & G. Kirchn., Arbor.
Muscav. [Petzold & Kirchner]: 301. 1864
: Pyrus latifolia f. acutiloba Irmisch, Blumen-Zeitung 29:
164. 1856
= Sorbus xacutisecta R. Reuther & O. Schwarz, Wiss.
Z. Padag. Hochsch. Erfurt-Muhlhausen, Mat.-Naturwiss.
Reihe 7(1): 54. 1971 ‘‘Sorbus acutisecta’’
Diploidy suggests hybrid origin and sexuality in Thuringian Sorbus
123
= Sorbus xheilingensis Dull, Ber. Bayer. Bot. Ges. 34: 47.
1961 ‘‘Sorbus heilingensis’’
= Sorbus xisenacensis R. Reuther, Haussknechtia 6: 17.
1997 ‘‘Sorbus isenacensis’’
= Sorbus xmulticrenata Bornm. ex Dull, Ber. Bayer. Bot.
Ges. 34: 49. 1961 ‘‘Sorbus multicrenata’’
= Sorbus xparumlobata (Irmisch) Petz. & G. Kirchn.,
Arbor. Muscav. [Petzold & Kirchner]: 302. 1864
: Pyrus latifolia f. parumlobata Irmisch, Blumen-Zeitung
29: 164. 1856
= Sorbus xtomentella Gand., Fl. Lyon. [Gandoger] 90.
1875 ‘‘Sorbus tomentella’’
= Sorbus xvagensis Wilmott, Proc. Linn. Soc. London 146:
78. 1934
The wide-spread assumption that F1 or early diploid
hybrids of the combination S. aria 9 S. torminalis are sterile
and only scarcely found between the parents does not apply
for Thuringia. Here, considerable numbers of diploid hybrid
individuals occur and not only spread by suckering but also
by seeds. Populations resulting from hybridization contain
alleles from parental taxa, but ongoing hybridization is not
increasing the frequency of those alleles. Such introgression
is part of the evolutionary process and should not preclude
protection of taxa (Allendorf et al. 2001). However, in our
opinion these hybrid populations should not receive the
same conservation status as apomictically fixed Sorbus taxa
(for a discussion see Gregor and Matzke-Hajek 2002).
Studied Thuringian Sorbus populations should be rather
conserved at the habitat level due to the unique presence of
considerable and evolutionary dynamic populations.
Acknowledgments We particularly thank K. Helmecke (Blan-
kenhain/Wittersroda) and P. Rode (Eisenberg) for their field work,
review, collection support, discussions, and teamwork. Ralf Hand,
Berlin, helped with Sorbus collection in Rhineland-Palatinate. The
Gesellschaft zur Erforschung der Flora Deutschlands (GEFD) pro-
vided opportunities for the establishment of the Sorbus working
group. We also thank F. K. Meyer (Jena) and the foresters D. Dubetz
(Arnstadt) and A. Scholer (Heilingen) for their guidance and support.
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