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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