Abstract: Carnivorous plants are specialized plants that derive some or most of their major nutrients by trapping and digesting small animals, typically insects and other arthropods. In India, there are a total of 44 species of carnivorous plants and Karnataka has 2 families of carnivorous plants, i.e. Droseraceae and Lentibulariaceae. Droseraceae represents 3 species. Exploration of carnivorous plants from Karnataka collected Drosera genus with three species, dissected the specimens, conducted pollen and seed morphometry using SEM and recorded secondary data on the distribution of Droseraceae in South India.

Keywords: Carnivorous herbs, D. burmanii, D. indica, D. peltata, glands, spiny surface, testa cells

Introduction

Carnivorous plants are specialized plants that derive some or most of their major nutrients by trapping and digesting small animals, typically insects and other arthropods. They have evolved unique adaptations to grow in nutrient-poor environments, especially soils that lack sufficient nitrogen or phosphorus; this unique trait allows them to survive and prosper in habitats such as bogs, fens and sandy soil, where other plants might struggle. Approximately 860 species of carnivorous plants under 20 genera of 12 families were reported in the world; they are Lentibulariaceae, Droseraceae, Nepenthaceae, Sarraceniaceae, Cephalotaceae, Drosophyllaceae, Byblidaceae, Roridulaceae, Bromeliaceae, Eriocaulaceae, Stylidiaceae and Martyniaceae (Adam et al., 2020). In India, a total of 44 species of carnivorous plants under 5 genera belonging to 3 families, they are Droseraceae, Lentibulariaceae and Nepenthaceae, were reported, viz. Utricularia (38 species), Drosera (3 species), Nepenthes (1 species), Pinguicula (1 species) and Aldrovanda (1 species) (Santapau and Henry, 1976; Singh and Sanjappa, 2011; Zaman et al., 2011; Kamble et al., 2012). In Karnataka, 2 families of carnivorous plants are reported, i.e. Droseraceae and Lentibulariaceae. Droseraceae represents 3 species. Flora of Bangalore district by Ramaswamy and Razi, (1973) documented a total 2 species, under 1 genus, D. burmanni and D. indica. Flora of Hassan district by Cecil J. Saldanha and Dan H. Nicolson, (1976) recorded 3 species under 1 genus, D. burmanni, D. indica and D. pelteta. A Synoptic Flora of Mysore district by Rao and Razi, (1981) reported species 3 under 1 genera, D. burmanni, D. indica and D. peltata. Flora of Chikmagalur district, Karnataka, India by Yognarsimhan et al., 1981 have listed 2 species under 1 genus D. burmanni and D. peltata. Flora of Karnataka Analysis by Sharma et al., (1984) has 3 species under the 1 genus, D. burmanni, D. indica and D. pelteta. Flora of Eastern Karnataka written by N. P. Singh, (1988) reported 2 species, 1 genus, D. burmanni and D. indica. Flora of Coorg (Kodagu) Karnataka, India by Keshava Murthy and Yoganarasimhan, (1990) have reported the 3 species, D. burmanni, D. indica and D. peltata under 1 genus. Flora of Gulberga district by Seetheram et al., (2000) has not reported any species. Flora of Shivmogga district by Ramaswamy et al., (2001) has reported 2 species under 1 genus, D. burmanni and D. indica. Flora of Udupi district by Gopalkrishna Bhat, (2003) reported 2 species under 1 genus, D. burmanni and D. indica. Flora of Anshi National Park by Laxminarasimhan and Punekar, (2011) have reported 2 species under 1 genus, D. burmanni and D. indica. Flora of Tumkur district by Baskar and Kushalappa, (2014) have reported 2 species, under 1 genus, D. burmanni and D. indica Flora of South Kanara has not reported any species.

Flowering plants of Western Ghats, India by Nayar et al., (2014) have reported 3 species, under 1 genus, D. burmanni, D. indica and D. pelteta.  Flora of Gadag district by Kotresha and Kambhar, (2016) have reported 2 species under 1 genus, D. burmanni, D. indica. Flora of Haveri have reported 1 species, under 1 genus, D. indica. Flora of Bidar district, Karnataka by Seetharam et al., (2018) have reported 1 species under 1 genus, D. indica. Flora of Kolar district by Yoganarsimhan et al., (2018) have reported 1 species under 1 genus, D. burmannii. Floristic diversity status and utility in Raichur district by Savita and Kotresha reported 2 species under 1 genus, D. buramnnii and D. indica. Numerous floristic studies have documented the occurrence of Drosera species across Karnataka and other parts of South India (Ramaswamy and Razi, 1973; Saldanha and Nicolson, 1976; Rao and Razi, 1981; Sharma et al., 1984; Nayar et al., 2014). However, these studies primarily focused on taxonomy, distribution of species and comparative pollen and seed morphometric analyses remain limited. SEM Photographs of pollen and seed provide taxonomic evidence for species.

Pollen and seed morphometric works

The genus Drosera has pollen with a proximal aperture and an extremely peculiar structure (Kuprianova, 1973). The heteropolar pollen grains of Drosera (Droseraceae) are united into permanent tetrads. These tetrads have unique, complex internal set-ups, the apertures (pores) are situated equatorially and show protrusions along the borders of adjoining pollen grains, which are enclosed by a thick intine and emerge from the apertures. The tetrahedral tetrads sometimes are shifted to a small degree, mimicking tetragonal tetrads depending on the species and degree of hydration. Pollen ornamentation in all investigated Drosera species is echinate with numerous small bacula or clavae between the echini. Number and length of the echini differ considerably in a species-to-species manner. Pollen tetrad in Drosera seems to be one of the most intricate pollen grains in angiosperms. Drosera burmanni has pollen grains similar to those of Drosera sessilifolia, showing no developed cross wall, possession of aperture type 6, but the processes of the former are somewhat differentiated into the larger (0.4 µm in diameter) and the smaller ones (less than 0.2 µm in diameter). On examining the pollen grain under a light microscope; D. burmannii has 20-30 proximal pores per unit area and absence of cross wall. Pores lining along the connection area, about 15 in number arranged in a whorl. In electron microscope, spinules are 1.9 µm long and 0.4-0.7 µm wide at the base; about 100 in number per unit area. The shape of spine-like projections is variable from specimen to specimen. Whereas, D. indica pollen grains observed under a light microscope show united tetrahedral tetrads by cross wall cohesion. Each grain provided with one central pore, 8-12 developed channels and has type 7 aperture and the pollen grain processes pinular layer 1.5-1.9 µm thick. In electron microscope, spines l.8-2.3 µm long and 0.7 µm wide at base, 5-8 in number per unit area. Spinules 0.5 um long and 0.2 µm wide at base, drumstick in shape, 100 or more in number per unit area and basal layer 1 µm thick (Takarashi and Sorma, 1982). The present study provides a comparative scanning electron microscopy SEM investigations of pollen and seed analysis of all three Drosera species occurring in South India, namely D. burmannii, D. indica and D. peltata. Provided morphometric data helps to evaluate interspecific variation and to identify characters useful for species identification. The present study provides a comparative SEM-based evaluation of pollen tetrads, seed and testa cell patterns of D. burmanii, D. indica and D. peltata.

Material and methods

Study area:  South Indian states include Andhra Pradesh, Telangana, Karnataka, Kerala and Tamil Nadu. Karnataka, Kerala and Tamil Nadu records Western Ghats side by Arabian sea. Andhra Pradesh, Telangana and Tamil Nadu records Eastern Ghats. Western Ghats covers evergreen, semi-evergreen, moist deciduous, shola grasslands, riparian vegetation and scrubby forests. Eastern Ghats covers tropical evergreen, semi-evergreen, and moist deciduous to dry savannah and scrub forests.

Micro (pollen) and macroscopic (seed) analysis:   Fresh flowers and mature fruits of each species were collected during field surveys. Pollen grains were examined under a light microscope for preliminary observations, while mature seeds were used for scanning electron microscopic (SEM) analysis. Seed samples were mounted on aluminium stubs using double-sided carbon adhesive tape, sputter-coated with gold and examined under SEM following the procedure described by Deshi et al., (2025).

Scanning electron microscopy (SEM) and morphometric analysis of pollen and seeds: For each of the three Drosera species, three mature flowering individuals collected from natural populations were examined. Herbarium specimens were prepared following standard herbarium techniques (Rao and Jain, 1976) and deposited in the Herbarium of Karnatak Science College, Dharwad (HKSCD).