Journal
of Threatened Taxa | www.threatenedtaxa.org | 26 September 2021 | 13(11):
19640–19644
ISSN 0974-7907 (Online) | ISSN 0974-7893 (Print)
https://doi.org/10.11609/jott.7367.13.11.19640-19644
#7367 | Received 27 April 2021 | Final received 07 August
2021 | Finally accepted 19 August 2021
A cytomorphological investigation
of three species of the genus Sonchus L. (Asterales: Asteraceae) from Punjab, India
M.C. Sidhu 1 & Rai
Singh 2
1,2 Department of Botany, Panjab
University, Sector 14, Chandigarh, Punjab 160014, India.
1 mcsidhu@gmail.com, 2 raibot95@gmail.com
(corresponding author)
Editor: M.I.S. Saggoo,
Patiala, Punjab, India. Date of publication:
26 Septtember 2021 (online & print)
Citation: Sidhu, M.C.
& R. Singh (2021). A cytomorphological investigation of three species of
the genus Sonchus L. (Asterales:
Asteraceae) from Punjab, India. Journal of
Threatened Taxa 13(11): 19640–19644. https://doi.org/10.11609/jott.7367.13.11.19640-19644
Copyright: © Sidhu & Singh 2021. Creative
Commons Attribution 4.0 International License.
JoTT allows unrestricted use, reproduction,
and distribution of this article in any medium by providing adequate credit to
the author(s) and the source of publication.
Funding: None.
Competing interests: The authors
declare no competing interests.
Acknowledgements: The authors are thankful to the
chairperson, Department of Botany, Panjab University Chandigarh for providing
necessary facilities during this investigation.
Abstract: Three species of the genus Sonchus L. (Sonchus
asper, S. oleraceus and S. wightianus) were collected from the Malwa
region of Punjab during 2019 to 2020. These species were studied for
cytomorphological variations. The species under investigation were identified
based on their morphological descriptions. Sonchus
asper (L.) Hill and Sonchus wightianus DC. possess the same number of chromosomes
(2n=2x=18) whereas Sonchus oleraceus (L.) L. is tetraploid with 2n=4x=32
chromosomes. Chromosome number of S. wightianus
(2n=2x=18) was worked out for the first time from the state of Punjab. Sonchus olereceus
has larger pollens than S. asper and S. wightianus.
This study will be useful for researchers, taxonomists and cytologists for
accurate identification of these three species.
Keywords: Chromosome number, involucral
bract, meiosis, palynology, Sonchus, taxonomy.
Sonchus L. is a member of the family
Asteraceae with 95 species distributed throughout the world including western
Morocco, Ethiopia, southern Sudan, South Africa, Canary Island, Europe, Iran,
Iraq, Egypt, Afghanistan, and Turkistan (Boulos 1960; Cho et al. 2019). Sonchus species are annual to perennial herbs with a
milky latex. The stem is clasping, toothed or pinnatifid, segmented leaves;
terminal, umbellate, yellow, ligulate-homogamous heads; ovoid, ellipsoid,
compressed, ribbed achenes with white hairy pappus which are the important
features of the genus Sonchus L. (Quireshi et al. 2002; Rahman et al. 2008). Earlier four
species of Sonchus (S. asper Vill., S. arvensis L., S. oleraceus L., & S. maritimus
L.) were reported from British India (Hooker 1882) and undivided Punjab (Bamber
1916). Sharma (1990) enlisted S. asper, S. oleraceus,
and S. wightianus from Punjab. Later on, Sidhu
(1991) recorded S. asper, S. arvensis, and S. oleraceus
from the state of Punjab. Sonchus asper
and S. oleraceus were common in the previous studies
whereas S. wightianus or S. arvensis
were frequently misplaced under confusing species.
Morphological
parameters have been used for the identifications of plant species for a long
time. It is one of the basic, simple and cost effective tools. Morphological
features such as leaf shape and color; flower color and type; number, position and nature of androecium
and gynoecium; shape and type of fruit and seeds are used for identification of
species (Singh & Dey 2005). Chromosome number is
also important in the identification of species because species, genera and
families have their own unique chromosome numbers in general and basic
chromosome number in particular. Variations in chromosome numbers are useful in
taxonomic studies (Raven 1975; Jones 1979).
The present
study is an attempt to differentiate between previously reported two (S.
arvensis and S. wightianus) species
(Sharma 1990; Sidhu 1991). Therefore, it is important to look into the detailed
morphology of the three species under investigation. Keeping this in
view, the present study has been planned to characterize three species of Sonchus from the state of Punjab based on
morphological and cytological observations.
Materials and Methods
Collection of study materials
The present study has been
undertaken in the Malwa region of the state of
Punjab, India. The study material of three species of Sonchus
was collected during 2019 to 2020. The collected plant specimens were cleaned
thoroughly, pressed, and dried at room temperature. After this, the plant
specimens were pasted on herbarium sheets. Herbarium specimens were
deposited in the Herbarium, Department of Botany, Punjab University Chandigarh
(PAN-21994, 21996 and 21997).
Morphological study
Morphological features of a leaf
(arrangement, shape, type, color), stem (glabrous, hairy), flower (colour, type, shape), androecium
(number, shape, nature), gynoecium (shape, number, nature) were examined to
establish the identity of each of the three Sonchus
species. The available literature (Hooker 1882; Bamber 1916; Turner et al.
1961; Walter & Kutta 1971; Boulos 1972; Hsieh et
al. 1972; Nair 1978; Mejias & Andres 2004; Cho et
al. 2019) have been looked into to describe the Sonchus
species in question. The Herbarium, Department of Botany, Panjab University
Chandigarh and online Herbaria have also been consulted for identification.
Meiotic and pollen study
Meiotic analysis has been carried
out in three Sonchus species to examine their
chromosome numbers. Young flower buds were collected and fixed in the fixative
(ethanol 3: glacial acetic acid 1) for 24 hours then shifted to 70% ethanol
till further use. Anthers were excised from young flower bud on the glass slide
having a drop of acetocarmine and crushed with the help of a glass rod. The
material was covered with a micro cover-slip and pressed in two folds of filter
paper after gentle heating. Slides were observed under the microscope.
Photographs of the pollen mother cells containing countable chromosomes have
been taken. For pollen study, mature anthers were taken on the slide and squashed
in glycerol acetocarmine (1:1), covered with a cover-slip and observed under
the microscope after 24 hours. Uniformly stained pollens (S.P.) were considered
fertile whereas, poorly stained or unstained pollens as sterile. The percentage
of pollen fertility was calculated using (Pollen fertility = S.P. / Total
Pollens x 100) formula. Pollen size has been measured with the help of camera-lucida technique.
Results and
Discussion
Three species of the genus Sonchus, i.e., Sonchus
asper, S. oleraceus, and S. wightianus were collected from the Malwa
region of Punjab during 2019 to 2020. All the three species are annual with
erect habit. Leaves of S. oleraceus are
smooth, glabrous, and light green whereas they are
dark green in the case of S. wightianus. In S.
asper, leaves are spined and bluish-green. Leaves
are elliptic-oblong, half amplexicaul with round auricles in S. asper
and S. wightianus but auricles are spreading
in the case of S. oleraceus (Image 1,2).
Similarly, leaf auricles were found to be round in S. asper and pointed
to acute in S. oleraceus (Barber 1941; Quireshi et al. 2002; Cho et al. 2019). S. asper and
S. oleraceus are very similar to each other in
flower colour, i.e., pale yellow to dark yellow whereas the flower colour in S.
wightianus is orange yellow. Involucral
bracts are smooth in S. oleraceus, glandular
hairy in S. wightianus and spiny-hairy in S.
asper (Image 2). Rahman et al. (2008) also observed glandular and hairy involucral bracts in S. wightianus
which supports the present study. This feature is important and useful for
establishing the identity of S. wightianus.
Achenes are wrinkled with ribs in S. asper, compressed in S. oleraceus and finely compressed in S. wightianus (Image 3).
Identification key (morphology)
1 (a) Leaf auricles
acute………………….… S. oleraceus
1 (b) Leaf auricles
round………….……………….………. 2
2 (a) Involucral
bracts with glandular hairs ……………
....................................................……. S. wightianus
2 (b) Involucral
bracts with spiny hairs ……. S. asper
Both Sonchus
asper and S. wightianus are diploid and
contain 2n=2x=18 chromosomes. Nine bivalents were observed at diakinesis and metaphase-I in S. asper and equal
segregation of chromosomes (9-9) at anaphase-I in S. wightianus
(Image 4.a,b,d). Razaq et al. (1994) also
reported chromosome numbers 2n=18 in both Sonchus
asper and S. wightianus and 2n= 32 in S.
oleraceus from Pakistan.
Sonchus oleraceus is a tetraploid and has shown 16
bivalents at diakinesis stage (Image 4c). Present
chromosome findings of S. oleraceus is in
consonance with Ishikava (1911) who also reported
2n=4x=32 chromosome in this species. It has suggested the genetic stability of
species even after more than 100 years. But a diploid form of S. oleraceus (2n= 16) and tetraploid (2n= 32) were
previously reported by Marchal (1920) and Cooper
& Mahony (1935), respectively. More studies had described S. asper
as diploid (2n= 18) and S. oleraceus as
tetraploid (2n= 32) (Turner et al. 1961; Walter & Kutta
1971; Boulos 1972; Hsieh et al. 1972; Gupta & Gill 1983; Sidhu et al. 2011;
Kaur & Singhal 2015). The variation of chromosome number in Sonchus species points towards the incidence of
aneuploidy that has happened over time in the genus Sonchus.
Pollen size of S. oleraceus is 36.25 x 32.5 μm–40
x 33.75 μm followed by S. wightianus
(33.75 x 32.5 μm–36.25 x 33.75 μm)
and S. asper (31.25 x 28.75 μm–35 x 32.5 μm) (Image 5 a–c). Pollen size of S. asper and S.
wightianus is almost similar which may be due to
the same number of chromosomes (2n=2x=18). Pollens of S. oleraceus
are larger than the other two species which may be because of its tetraploid
(2n=4x=32) nature. Pollen fertility was maximum in S. oleraceus
(94.33%), followed by S. wightianus (92.13%)
and S. asper (88.88%). High pollen fertility in S. oleraceus suggested that it is an allotetraploid. These
observations are in consonance with Poole (1932) who found that amphidiploids
possess a greater degree of pollen fertility.
Earlier three species of Sonchus such S. asper, S. oleraceus, & S. wightianus
(Sharma 1990) and S. asper, S. oleraceus, &
S. arvensis (Sidhu 1991) were documented from the state of Punjab,
India. But according to available
literature (Shumovich & Montgomery 1955; Mamgain 1998) S. arvensis grows exclusively in
Europe and is likely confused with S. wightianus
in India. In literature, from the state
of Punjab third species of Sonchus was
considered as S. arvensis but it is actually a S. wightianus.
Cytological details of Sonchus species are also incomplete from the state
of Punjab, India. Previously, Gupta & Gill (1983) had worked out chromosome
numbers of three Sonchus species (S. asper
(L.) Hill, S. brachyotus DC and S. oleraceus L.) from the state of Punjab. However, they
have not worked out the chromosome of S. wightianus.
Consequently, information about the chromosome number of S. wightianus is not known. Therefore, the present study
has been carried out for cytomorphological characterization of Sonchus species from the state of Punjab India. The
findings of the present study will be useful for researchers, cytologists, and
taxonomists for correct identification of Sonchus
species based on morphological, cytological, and palynological details.
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