Systematic Study of Genus Nepenthes L. (Nepenthaceae) in Western Sarawak, Borneo

NURUL NABILAH HUDA, MOHD HISHAM (2024) Systematic Study of Genus Nepenthes L. (Nepenthaceae) in Western Sarawak, Borneo. Masters thesis, Universiti Malaysia Sarawak.

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Abstract

Nepenthes is the sole genus of the monotypic family known as Nepenthaceae, under the order of Caryophyllales. This genus is native to Southeast Asia with Borneo and Sumatra being the centre of its diversity. Nepenthes are known as highly studied carnivorous plants for their unique morphological characteristics, ecology, carnivorous syndrome, ethnobotanical, phytochemical, and pharmacological properties. Hence, this study focused on revising and comparing the morphological characteristics of Nepenthes that are distributed particularly in western Sarawak as well as identifying the anatomical, micromorphological, and palynological characteristics of the Nepenthes studied. Distribution and ecology of each Nepenthes taxa were also studied. A total of eighteen taxa were recorded from western Sarawak (Samarahan, Kuching, Serian, and Samarahan). Most of the taxa were examined based on fresh samples collected from the field; Nepenthes albomarginata, N. ampullaria, N. gracilis, N. hirsuta, N. hispida, N. mirabilis, N. mirabilis var. echinostoma, N. nazreeana sp. nov. ined., N. rafflesiana and others. The remaining five taxa; N. bicalcarata, N. northiana, N. veitchii, N. tentaculata, and N. x bauensis were examined based on herbarium specimens deposited in SAR. The morphological examination revealed that the Nepenthes studied has interspecific and intraspecific variation among the taxa. The anatomical studies of 13 collected Nepenthes taxa under the light microscope were focused on two parts; the epidermal layers, and the midrib. The stomatal complex type of Nepenthes studied are all anomocytic either with straight, or sinuous type of anticlinal walls on their abaxial or adaxial surfaces. Additional data from Field Scanning Electron Microscopy revealed that the stomata have three types of formation; sunken, raised, and semi-raised. They are developed in various sizes and densities among the polygonal epidermal cells. The sessile glands also were noticed to appear mostly on the adaxial surfaces of leaves. Meanwhile, the midrib cross section shows four types of outer shapes with different vascular bundle arrangements and have a complex closed vascular system with consistent closed, collateral vascular bundles. The micromorphological characteristics were observed mainly on the epidermal layers of the leaves, and the pitchers of Nepenthes under FESEM. Trichomes were present mostly on the abaxial surfaces of the leaves compared to the adaxial surfaces. More than five types of trichomes were identified and all of them were categorised into two which are glandular trichomes and non-glandular trichomes. The examination of the inner surface of the pitcher depicted a variety of features such as the lunate cells and the digestive glands. The lunate cells were found distributed abundantly on the upper part of the pitcher body which is known as the waxy zone. Ten taxa from the 13 Nepenthes studied own these features that are formed in a crescent-like shape which bends downwards and elongate horizontally in various lengths. Meanwhile, the digestive glands were observed present on the inner surface of the pitcher of all 13 Nepenthes studied. Most of them are developed in the basal half of the pitcher, known as the digestive zone. The digestive glands are conspicuously different in sizes and density among the 13 taxa studied. The palynological study focused on six Nepenthes taxa; N. ampullaria, N. gracilis, N. mirabilis, N. nazreeana sp. nov. ined., N. rafflesiana, and N. reinwardtiana are tetrahedral tetrad and inarpeturate with echinate-microechinate ornamentation. The sizes of the pollen tetrads of the six Nepenthes studied are slightly varied between 17.02-19.91 µm in diameter, and all of them were identified as small size which falls between 10-25 µm. The pollen characteristics are homogenous among the six Nepenthes taxa studied. Therefore, they are not possessing any taxonomic value that can help in delimiting the taxa in the genus. But, they can be differentiated by their sizes, which can be influenced by the environment or the methods used to observe the pollen.

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