MORPHOLOGICAL STRUCTURES OF RHIZOPHORA APICULATA BLUME. and RHIZOPHORA MUCRONATA LAM

aDepartment of Plant Science, Kulliyyah of Science, International Islamic University Malaysia, Kuantan, Pahang, Malaysia b International Institute for Halal Research and Training (INHART), International Islamic University Malaysia, Kuantan, Pahang, Malaysia c Department of Marine Science, Kulliyyah of Science, International Islamic University Malaysia, Kuantan, Pahang, Malaysia *Corresponding Author Email: firdawila@iium.edu.my


INTRODUCTION
The mangrove forest is one of the plant ecosystems that thrive in the moist soil of tidal zones. A group researchers identified over 30 families of mangrove plants (Minobe et al., 2010). They acknowledged their ecological and economic values in a multitude of aspects, including timber and firewood sources, ideal habitats for diverse wildlife, biological defense from tsunami and storm, and erosion mitigation (Ong et al., 2004;Hashim et al., 2010). The mangrove ecosystem is found along the intertidal areas with high salinity and high tidal conditions (Sheue et al., 2013). Due to extreme high salinity conditions and tidal water in the coastal areas, the mangrove forests have evolved, making them unique mangrove species with adaptation abilities that can withstand the harsh conditions (Mohd-Arrabe and Noraini, 2013;Samaddar and Jayakumar, 2015). The mangrove family, Rhizophoraceae, consists of 16 genera and 149 species worldwide that tend to thrive in tropical and subtropical coastal mangrove ecosystems (Balasubramanian et al., 2015). Rhizophoraceae is the most diverse mangrove family, consisting of four exclusive genera: Rhizophora, Bruguiera, Ceriops and Kandelia. They are classified as true mangrove species, distributed mainly in the intertidal zones (Sheue et al., 2013;Setyawan and Ulumuddin, 2012). Rhizophora is the largest genus in the Rhizophoraceae family, consisting of three main species: R. mucronata, R. stylosa and R. apiculata, as well as two hybrids species: R. x lamarckii and R. x annamalayana (Setyawan and Ulumuddin, 2012).
Previous research on the medicinal value and usefulness of R. apiculata has been extensively published, as reported, that communities in Malaysia utilized R. apiculata with high tannin content to cure immunological disorders (Balasubramanian et al., 2015). Furthermore, as mentioned that the leaves of R. mucronata were utilized by the Indian Sundarban communities residing near mangrove areas to relieve angina (Abdul-Malik et al., 2015). This species is also economically significant as commercial mangrove wood and timber supplies in the Asia-Pacific regions. Its timber is primarily utilized to produce fishing stakes, wood pilings, charcoals, and wood chips, which are then converted into rayon (Ong et al., 2004). Rhizophora species is easily recognized morphologically by apparent features of its viviparous seed and pneumatophore roots. The viviparous seed is the most distinct characteristic of true mangrove species that allows it to adapt to water with high saline conditions. For adaptation purposes, the genus Rhizophora also possesses unique features that distinguish it from terrestrial plants, such as stilt root, succulent leaves with black dots beneath the leaves, and viviparous fruits (Mohd-Arrabe and Noraini, 2013). Morphological characteristics are among the most significant components considered by biologists in plant identification and classification for systematic studies. It is the simplest conventional method, performed based on observation on parameters such as root habit, stem habit, in addition to leaf, flower and fruit variations. Rhizophora species appears to be well-known; nevertheless, there is insufficient information on its distribution in Peninsular Malaysia in terms of morphological structures. Thus, the purpose of this research was to record and observe the morphological variations of R. apiculata and R. mucronata in selected locations across Peninsular Malaysia.

MATERIALS AND METHODS
The plant samples were collected in three different locations in Peninsular Malaysia: (1) Sungai Kong Kong, Masai, Johor, (2) Sungai Kemaman, Kemaman, Terengganu, and (3) Cherating and Sungai Pahang, Pahang. The collected sample processed as voucher herbarium specimen. The morphological structures of R. apiculata and R. mucronata were studied based on the descriptions provided (Duke and Bunt, 1979;Mathew, 1994;

RESULTS AND DISCUSSION
The vegetative and reproductive structures of R. apiculata and R. mucronata from three locations were recorded and annotated. The recorded parameter was summarised in (Table 1 and Table 2). Following rigorous examinations, it was determined that morphological structures or features could be utilized to distinguish R. apiculata ( Figure 1) from R. mucronata ( Figure 2). According to the available data, both species may reach a height of 30 metres in all study locations. R. apiculata and R. mucronata have fissure stem habit. However, the distinction between these two is that fissure in R. apiculata is vertical but horizontal as far as R. mucronata is concerned. Furthermore, R. apiculata has a dark grey stem, but R. mucronata has a dark black stem, which distinguishes them (Setyawan and Ulumuddin, 2012). Morphological studies on the tree stem habit are prominent in taxonomy; studied plant structured to identify woody plant species (Cantrill and Poole, 2005;Yunus et al., 1990). In terms of locations, there were no variations in the parameter for both species. R. apiculata has a narrowly elliptic-oblong leaf shape. These findings were consistent with (Haining and Boufford, 2007;Ragavan, 2015).
Stipules serve as sturdy enclosures for young shoots in Rhizophoraceae species. This structure is crucial in plant identification and classification. According to a study, the morphology of stipules may be utilised to differentiate plant species in the Rhizophoraceae family from other plant genus and to classify all Rhizophora species owing to stipule variations  (Sheue et al., 2012). This research discovered that R. apiculata and R. mucronata had distinct coloured stipules. Thus, the colour of stipules distinguished them. Based on the observations, R. apiculata had red stipules, but R. mucronata had light green stipules, and this finding was supported (Sheue et al., 2012). The stipule and its morphological characteristics are important in the taxonomic study; investigated stipules in the Coccocypseleae and Kandelia genus studies, respectively (Piesschaert et al., 2000;Sheue et al., 2003).
R. apiculata has 2-flower cymes per peduncle in terms of inflorescence, but R. mucronata has 2-5-flower cymes per peduncle. Both species have four sepals and four petals per flower; however, the colours of the sepal distinguish these two species. R. apiculata has yellow sepals, but R. mucronata has creamy white sepals. Some researchers supported the comparison of flower characteristics between R. apiculata and R. Mucronata (Setyawan and Ulumuddin, 2012;Ragavan, 2015). The significance of flower morphological characteristics in the systematic study, nevertheless, was not only limited to Rhizophora species.
In fact, according to some study also, the floral structure of Zingiberaceae was the most significant plant part for observation and analysis (Box and Rudall, 2006;Sakai and Nagamasu, 2000). One of the distinguishing features of the Rhizophora genus is that it is viviparous (Tomlinson and Cox, 2000). R. mucronata was recorded to have a bigger hypocotyl size compared to R. apiculata. R. mucronata may grow and reach approximately 60 cm long, whereas R. apiculata may grow to be 35 cm long. The morphology shape of hypocotyl varies for R. apiculata and R. mucronata. R. apiculata was confirmed to have a cylindric-clavate shape, but it was a long cylindrical shape for R. Mucronata (Setyawan and Ulumuddin, 2012;Ragavan, 2015).

CONCLUSION
These findings supported the hypothesis that morphological structures were beneficial in identifying, classifying, and differentiating R. apiculata and R. mucronata. Both exhibit morphological variations in selected vegetative and reproductive features such as stem, leaf, and flower parts. This research established that there were no distinguishing characteristics of morphological structures of R. apiculata and R. mucronata collected from three locations. However, the data revealed quantitative data variations in morphological structures, such as the height and width of the species samples. In conclusion, the data presented in this study could be utilised to supplement future Rhizopora species studies.

ACKNOWLEDGEMENT
We thank the financial support by the grant research of International Islamic University Malaysia (LL(R2) -ECC/2(UIAM-17).
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