LM, Micromorphology, SEM of Leaf and Molecular Characterization of the Genus Cinnamomum (Family Lauraceae) Found in Sri Lanka: Taxonomic Significance

Abstract

Family Lauraceae is one of the most important plant families since members of this important family are used for different purposes such as food, spices and medicines. Sri Lanka is the principal global true cinnamon (C. zeylanicum) producer (80-90%) in the world. Apart from C. zeylanicum, there are seven underutilized Cinnamomum species. For efficient utilization approaches of the Cinnamomum species and proper conservation purposes, correct identification and characterization of these species are very important. Environmental plasticity may greatly influence the plants' morphology making it difficult to rely only on vegetative morphology and may not be a reliable source of information to differentiate the Cinnamomum species. Flowers are rarely found and flowering time varies among the species. Therefore, this study aimed to examine the leaf anatomy using standard protocols for light microscopy and scanning electron microscopy (SEM) of the eight species of Cinnamomum that occur in Sri Lanka to evaluate their potential utility in taxonomic differentiation. Moreover, molecular characterization of this genus using different universal barcoding regions of the cpDNA (trnL intron, the trnT-trnL, trnL-trnF, and trnH-psbA intergenic spacers) and internal transcribed spacer (ITS) of nuclear ribosomal DNA (rDNA) to check whether these sequences are reliable for species discrimination. Internal anatomy and leaf surface micromorphology were studied using standard light microscopy and scanning electron microscopy respectively. Some key petiole anatomical characteristics were stone cell characters, the structure of vascular bundle, the presence or absence of winged extensions, the presence or absence of trichomes, and the shape and outline of the petiole. Leaves were hypostomatic with no special arrangement for epidermal pavement cells. Simple, unicellular, unbranched, solitary and non-glandular trichomes were observed in different species on both surfaces of the leaves. Both adaxial and abaxial surfaces in C. dubium and C. rivulorum were densely covered with simple, unicellular/falcate, long and thin trichomes. Transverse sections of leaves along the midrib were different in shape (symmetrical, asymmetrical, boat, irregular, saucer). The midrib contained one open arch, a central vascular bundle that was with different in shape (oval, elongated, irregular, ‘V’, partially dissected into 2 or 3 segments) in different species. Micromorphology of cuticular materials on both abaxial and adaxial surfaces was different within and between species. Both abaxial and adaxial surfaces had undulating, thick cuticles with different patterns of wax deposition. Although it was possible to identify the single nucleotide polymorphism (SNP) of different universal barcoding regions of the cpDNA of different species, no sufficient sequence data were obtained to discriminate the species correctly.