Morphological and Leaf Anatomical Variation in the Genus Schefflera J.R.Forst. & G.Forst. (Araliaceae) along an Altitudinal Gradient in Gunung Mulu, Sarawak

Siti Noor Aishah, Binti Mohd Noor (2019) Morphological and Leaf Anatomical Variation in the Genus Schefflera J.R.Forst. & G.Forst. (Araliaceae) along an Altitudinal Gradient in Gunung Mulu, Sarawak. Masters thesis, Universiti Malaysia Sarawak (UNIMAS).

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Abstract

Genus Schefflera J.R.Forst. & G.Forst. is a genus in family Araliaceae (Ginseng family), which can be found abundant in high elevations and are usually can be found as shrub, epiphyte, climber, and small tree. With 1412 species worldwide, this genus is considered as the biggest genus in family Araliaceae. However, the systematic study of Schefflera in Borneo generally and Sarawak specifically is never being done and poorly understood. In this study, there was a total of 20 Schefflera taxa that have been documented in Gunung Mulu National Park, which is one of the World Heritage Site listed by UNESCO and the largest national park in Sarawak. Gunung Mulu National Park consists of three mountains namely, Gunung Mulu (2376 m), Gunung Api (1710 m) and Gunung Benarat (1615 m). This national park also has a broad range of rainforest structures on several types of soil. Out of 20 Schefflera taxa documented for Gunung Mulu National Park, 12 taxa were recorded on Gunung Mulu alone. A key is provided for all 20 Schefflera taxa in Gunung Mulu National Park. Anatomical observations were conducted on species found and collected from Gunung Mulu. The present study reveals that Schefflera had variety of morphological and anatomical characteristics along the altitudinal gradient of Gunung Mulu. In terms of morphology, some taxa in low elevation tend to have thinner lamina and larger leaves size. On the other hand, some taxa in higher elevation tend to have hairs on the abaxial surface, revolute leaf margin, thicker lamina, smaller leaves size and glossy leaves surface. In terms of anatomy, additional sclerenchyma layer which present between the collenchyma layer and parenchyma cortex layer can only be observed in very low elevation taxa only (less than 100 m) such as S. mangiferifolia D.G. Frodin & A.Puad, S. brookeana ined. and Schefflera cf. hexaphylla. Other characteristics such as thin cuticle and chlorenchyma layers, thick epidermis, high stomata density and low leaf mass area (LMA) value also have been observed in low elevation taxa. In contrast, characteristics such as thick cuticles and chlorenchyma layers, thin epidermis, low stomata density and high LMA value have been observed in high elevation taxa. The morphological and anatomical characteristics each of Schefflera taxa studied show that this genus is adapted well in their respective habitats, thus improve the efficiency of the physiological processes. Schefflera mjoebergii Merr. was the only species with trichomes on its abaxial surface of its lamina and petiole. Other taxon such as Schefflera cf. remotiserrata can be discriminated by the absence of hypodermis at its lamina and the occurrence sinuous pattern of anticlinal walls at the adaxial layer. There were also some common anatomical characteristics of this genus that have been observed in this study such as the presence of stomata at the abaxial surface only, occurrence of anisocytic stomata, occurrence of the sunken stomata, presence of aerenchyma cells at the spongy mesophyll layers, presence of druses and secretory canal at midrib and petiole. The anatomical keys have been constructed for ten taxa studied based on the arrangements of the vascular bundles in midrib and petiole. Keywords: Anatomy, elevations, Gunung Mulu National Park, morphology, Schefflera.

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