Pollen Morphology of Indian Species of Saraca L. (Leguminosae)-A Threatened and Legendary Medicinal Tree

Abstract

The genus Saraca L. (Leguminosae) is a universal panacea in herbal medicine. The present study investigates the comparative pollen morphology of four species of Saraca viz. S. asoca (Roxb.) de Wilde, S. declinata (Jack) Miq., S. indica L., and S. thaipingensis Cantley ex Prain growing in India to reveal differences of their pollen structures to aid taxonomic and evolutionary values. The detailed morphology and surface structure of pollen grains were studied and described using light microscopy and scanning electron microscopy. The pollen grains of Saraca showed isopolar, para-syncolporate, tricolporate, with radially symmetric, prolate and prolate-spheroidal structure. The surface of pollen of S. indica is rugulate with large lirae but in S. declinata, the surface is micro-rugulate to vermiculate with relatively thin lirae and that of S. thaipingensis is indistinct as the psilate surface with a frequent protuberance and fewer perforations were observed along with the gemmae like structure. Exine ornamentation helped to separate S. indica and S. asoca. Exine thickness varies from 3-4 μm. Presence of protuberance and exine thickness varies among individuals of the species spread over different locations. Present work also provides a unique palynological identity and interrelationship of these four species based on cluster analysis taking 23 pollen characters with the help of statistical method like the plotting of ternary graph. Ternary plots also helped to calculate the level of plasticity of each character in the intra-and inter-specific level.

Phylogenetic analysis of six different species of Saraca L. (Fabaceae, Caesalpinioideae) based on chloroplast matK gene

“…The morphological differences between S. asoca and S. indica are less pronounced than molecular differences. The morphological approach (Begum et al 2014) and the palynological approach (Sil et al 2019) have a sufficient though limited ability to identify different species. Molecular barcoding using the matK gene marker is, therefore, best suited for proper identification.…”

“…The sub-clade Amherstieae of the family Fabaceae (LPWG 2017) has a number of both medicinally and horticulturally important species. This tribe contains different species of Saraca along with other two genera, Endertia and Lysidice, based on the nature of their habitats (Estrella et al 2017), the number and nature of their stamen (Estrella et al 2018), and the ornamentations on their pollen grains (Sil et al 2019). The evaluation of phylogenetic relationships among different taxa of tribe Detarieae and three species of Saraca was done by Saha et al (2013).…”

“…S. indica L. (Figure 1.C) can be naturally found in different rainforests along with the populations of S. asoca (Preeti et al2012) from the central Himalayan foothills, eastern Himalayan forests, Gangetic basins, and western and eastern coasts of India Mohan et al 2017;Preeti et al 2012;Sil et al 2018). Determining the differences between these two species is a challenging task (Begum et al 2014) as their similar morphological natures and pollen morphologies make them difficult to properly distinguish (Sil et al 2019). S. declinata (Jack) Miq., commonly known as 'Red Saraca', is native to Malaysia (Zuijderhoudt 1967) and is characterized by reddish to saffron flowers, spreading bracteoles (Hou et al 1996), and pollen with a micro-rugulate surface (Sil et al 2019).…”

“…Determining the differences between these two species is a challenging task (Begum et al 2014) as their similar morphological natures and pollen morphologies make them difficult to properly distinguish (Sil et al 2019). S. declinata (Jack) Miq., commonly known as 'Red Saraca', is native to Malaysia (Zuijderhoudt 1967) and is characterized by reddish to saffron flowers, spreading bracteoles (Hou et al 1996), and pollen with a micro-rugulate surface (Sil et al 2019). S. declinata (= S. palembanica Miq., Figure 1.B), previously known as J. declinata Miq., (Hou et al 1996) is characterized by 3-4 stamens, spreading and deciduous to persistent bracteoles, and reddish flowers.…”

“…S. thaipingensis Cantley ex Prain (Figure 1.D) (Hou et al 1996) is another widely distributed species of Saraca native to Malaysia. Commonly known as the 'Yellow Saraca', it can be distinguished by its yellow flowers, enlarged bracts, single staminode, glabrous ovary (Sil et al 2018), and psilate surface of pollen grains with profuse protuberance (Sil et al 2019).…”