Systematics of medicinally important weeds of genus Convolvulus: Convolvulaceae

electron microscope (SEM). Results: Variations were observed in both the weeds, i.e Convolvulus arvensis (bindweeds) and Convolvulus prostatus (soft bindweed) in epidermal cells, stomatal size and number, guard cell shape and size, subsidiary cell and diversity of trichomes. Paracytic type of stomata was found in both the weed species. Stomata shape in Convolvulus is elliptical and oval to oval oblong in Convolvulus prostratus species have a and exine ornamentation. type was


INTRODUCTION
Convolvulaceae is one of the attractive eurpalynous family, consisting of herbs, shrubs, and vines. Family Convolvulaceae extending globally most abundantly in America and Asia. (Saensouk, 2007). According to Austin (1975), the family contains about almost 50 genera and 2000 or more species. There are about thirteen genera exist in Pakistan that includes both natives and cultivated (Ali et al., 1979 Convolvulaceae is divided into two groups Psiloconiae and Echinoconieae (Sengupta, 1972). Genus convolvulus was placed in Psiloconiace, Convolvulus arvensis L. bindweeds and Convolvulus prostatus (soft bindweed) are the most important medicinal weeds (Jaradat, 2005). Convolvulus arvensis is a perennial vine, persistent, spread by rhizome and seeds, having a cylindrical and branched stem. Leaves are variable in shape; triangular to ovate (Weaver and Riley, 1982). Species is native to Eurasia, but commonly distributed world wild and ranked as noxious weeds of the world (Austin, 2000;Holm et al., 1977).
Convolvulus arvensis was traditionally applied to treat epilepsy in north Pakistan Bahadur et al., 2018a;Murad et al., 2011).
Convolvulus prostatus is one of the important medicinal weed that is the main source of Shankhpushi, considered as the best brain tonics (Sethiya et al., 2009). Leaves powder of Convolvulus arvensis is used to treat boils and inflammation. Whole plant juice of Convolvulus prostratus is used as a Nerve tonic and the treatment of fever, jaundice (Qureshi et al., 2010;Waheed et al., 2020). First palynological survey on Convolvulaceae was made by Hallier in 1893.
Pollen grain morphology is very important for the identification of plants. According to Arora and Modi (2008), the Palynological evidence provides valuable information and conformation about genera and species that are closely related. Scanning electron microscope significantly improved the pollen surface (Ridgway and Skyvarla, 1969). Both light microscopy (LM) and scanning electron microscopy (SEM) are distinct interest for researchers to observe different taxonomic features. (Qureshi et al.,2019;Khan et al., 2017). Foliar anatomical characters are very important for correct identification. Specific kind of trichomes can be used frequently to delineate genera, species and family (Khan et al., 2013). Type of trichome is one of the main characters used in identification. The taxonomic value of the trichomes and their inference in systematic is well known (Cantino, 1990;Khokhar, 2009).
The main objective of the present research is to determine the medicinal uses of the two important weeds along with pollen grains morphology through scanning electron microscope (SEM) and foliar anatomical characters (Light microscopy) of the weed plants for correct systematic identification.

Plant collection and identification
Both the weeds of genus Convolvulus i.e

Convolvulus arvensis and Convolvulus prostratus
were collected during the period of March 2016 -May 2017. Five to six specimens were collected from a different locality. For correct taxonomic identification, the International Plant Name Index (IPNI) was used. Plant specimens were submitted in the Herbarium of Pakistan (ISL), Quaid-i-Azam University Islamabad, Pakistan (Table 1).

Foliar epidermal anatomy
Subrahmanyam technique was used for light microscopy, small pieces of the leaf are boiled in 4 mL of nitric acid and 0.2 g of potassium chloride in a test tube (Subrahmanyam, 1996). The epidermis was separated in the form of the thin pellicle. Both the abaxial and abaxial epidermal surface was separated and washed with ethanol so that extra stain was removed easily. Putting 1 to 2 drops of lactic acid on the epidermal strip covered with a coverslip. By using light microscope both the qualitative and quantitative characters were observed, and photographs were taken with the help of Nikon (FX-35) camera fitted on the Leica Light microscope (Model: DM 1000).

Pollen morphology
Pollen grains were prepared by using the technique of Erdtman (1953) for scanning electron microscopy (SEM). Pollen grains that are acetolyzed were suspended in 90% ethanol, mounted on stubs. Specimens were sputter-coated with gold and with the help of a scanning electron microscope (Model JEOL JSM-5910), photographs were taken ( Figures  1 and 2).

RESULTS AND DISCUSSION
Foliar epidermal morphological characters were observed with the help of a light microscope. Light microscopy plays a key role in the investigation of foliar epidermal characteristics. Previous records also show the importance in the delineation of other groups of plants taxa (Ullah et al., 2011;Munir et al., 2011;Riaz et al., 2010). A significant variation was observed in both the qualitative and quantitative characteristics. A taxonomic key was prepared for both weed plants i.e Convolvulus arvensis and Convolvulus prostratus. Different researchers also used these characters for the preparation of taxonomic key (Khan et al., 2017b).
Variation was observed in stomatal number, length width and stomatal index in both adaxial and abaxial surface. In Convolvulus arvensis the epidermal cell was found to be Polygonal on adaxial surface and both polygonal and irregular on abaxial surface. Mostly paracytic type of stomata is present which shows similar to the previous work of ( Tayade and Patil, 2011). Paracytic type of stomata was found in both the weed species. Shah. (1967) also reported three type of stomata i.e Paracytic, Anisocytic and Anomocytic during stomatal development in Convolvulus arvensis. The shape of stomata in  Convolvulus arvensis is elliptical and oval to oval oblong in case of Convolvulus prostratus (

and in
Convolvulus prostratus is 55.22 at the abaxial surface. Variation was also observed in epidermal cell size, shape, length and width. Variation was found in epidermal cell length width size and shape (Tables 3, 4 and 5).
Palynological characters of both the weeds were randomly measured. Both the quantitative and qualitative characteristics were shown in Tables 6 and 7. In the examined weed species Tricolporate pollen type was observed. The shape of pollen grains is Prolate, Perforate in both the species. Skvarla et al. (1976) and Wodehouse (1930) were also reported similar results. Perforate is the basis sculpturing in genus Convolvulus that is a primitive characteristic but the echinate sculpturing is one of the advance features observed in genus Ipomoea. According to Telleria and Daners (2003), a highly diverse pollen morphology of family Convolvulaceae having a unique taxonomic importance. A wide range of variation in size and sculpture was noted. P/E ratio is 1.37 in Convolvulus prostrates. Exine sculpturing is     (1969) and Muller (1969) Morphology of pollen is a very important taxonomic tool in the identification of higher plants. The present findings also encourage taxonomists to use the Light microscope (LM) and Scanning electron microscope (SEM) for the identification and complete phylogeny of medicinally important weeds.

CONCLUSION
The study plays a very important role in the correct identification and differentiation of two weeds of genus convolvulus. Palyno-morphological and foliar epidermal studies of weeds were determined. Both unicellular and multicellular (glandular and Nonglandular) are found in these weeds species. Capitate trichomes have been reported to secrete a small number of essential oil and flavonoids. Pollen micromorphological features play a vital tool in the systematics of these weed plant, afterward conservation of these weed species in the area.

CONTRIBUTIONS
All authors contributed to the research work. SA, and MN: performed experimental work. ANK, and SS: did sample collection and paper write up. MA, and MZ: supervised the work.