Rafflesia is a holoparasitic plant that depends solely on its host for its nutrients, given that during the early stage of its life, this parasite lives inside the host vine. The lack of host specificity and preference information for Rafflesia can largely be attributed to the absence of a comprehensive taxonomic study in Tetrastigma . Without the host, the Rafflesia will not be able to survive. Therefore, this research was conducted to study the host-parasitic relationships between the two species using anatomical dissection and micrographic images using a light microscope (LM) and scanning electron microscope (SEM). The anatomical study consisted of three stages of Rafflesia buds; the emergence of cupule stage, cupule-bract transition stage, and bract stage ­­attached with the host. All samples underwent sliding techniques and were observed using LM and SEM. Based on the results, the anatomical characteristics of the host-parasite for the cupule stage evidenced penetration of the parasite-affected tissues inside the vascular bundles with the visibility of the flower bud. However, during other stages, the penetration of parasite-affected tissues to the vascular bundles was disrupted and cannot be seen using this sliding technique. The endoparasite of Rafflesia invades the host only towards the phloem region in the early stage. In contrast, in late buds for both species, the Rafflesia tissue invaded both the host xylem (proximal region) and phloem. The parasite intrusion movement for both Rafflesia species showed a pointed tissue towards the host as this was believed to minimise the damage of the host plant. A new method using the paraffin wax technique might improve the sectioning and provide a more precise relationship dissection. The information from this study is expected to provide baseline information and an understanding of the host-parasitic relationship between the species. In addition, further anatomical studies with the different stages of buds will offer a better understanding of their relationship with the host.

• Aiman Hanis, J., Abu Hassan, Nurita, A. T., & Che Salmah, M. R. (2014). Community structure of termites in a hill dipterocarp forest of Belum-Temengor Forest Complex, Malaysia: Emergence of pest species. The Raffles Bulletin of Zoology, 62, 3-11.

• Bell, T. L., Adams, M. A., & Rennenberg, H. (2011). Attack on all fronts: Functional relationships between aerial and root parasitic plants and their woody hosts and consequences for ecosystems. Tree Physiology, 31(1), 3-15. https://doi.org/10.1093/treephys/tpq108

• Cameron, D. D., & Seel, W. E. (2007). Functional anatomy of haustoria formed by Rhinanthus minor: Linking evidence from histology and isotope tracing. New Phytologist, 174(2), 412-419. https://doi.org/10.1111/j.1469-8137.2007.02013.x

• Cocoletzi, E., Angeles, G., Ceccantini, G., Patrón, A., & Ornelas, J. F. (2016). Bidirectional anatomical effects in a mistletoe-host relationship: Psittacanthus schiedeanus mistletoe and its hosts Liquidambar styraciflua and Quercus germana. American Journal of Botany, 103(6), 986–997. https://doi.org/10.3732/ajb.1600166

• Crang, R., Lyons-Sobaski, S., & Wise, R. (2018). Plant anatomy: A concept-based approach to the structure of seed plants. Springer.

• Hibberd, J. M., & Jeschke, W. D. (2001). Solute flux into parasitic plants. Journal of Experimental Botany, 52(363), 2043-2049. https://doi.org/10.1093/jexbot/52.363.2043

• Lopes, W. A., Souza, L. A., Moscheta, I. M., Albiero, A. L., & Mourão, K. S. (2008). A comparative anatomical study of the stems of climbing plants from the forest remnants of Maringa, Brazil. Gayana Botanica, 65(1), 28-38. http://doi.org/10.4067/S0717-66432008000100005

• Malaysian Nature Society. (2013). About Belum Temengor and MNS. https://mnshornbillvolunteerprogramme.wordpress.com/about/

• Marcati, C. R., Longo, L. R., Wiedenhoeft, A., & Barros, C. F. (2014). Comparative wood anatomy of root and stem of Citharexylum myrianthum (Verbenaceae). Rodriguesia, 65(3), 567–576. https://doi.org/10.1590/2175-7860201465301

• Mursidawati, S., & Irawati (2017). Biologi konservasi Rafflesia [Conservation Biology Rafflesia]. LIPI Press.

• Mursidawati, S., & Sunaryo (2012). Studi anatomi endofitik Rafflesia patma di dalam inang Tetrastigma sp. [Study of the endophytic anatomy of Rafflesia patma in the host Tetrastigma sp.]. Buletin Kebun Raya, 15(2), 71-80.

• Mursidawati, S., & Wicaksono, A. (2020). Tissue differentiation of the early and the late flower buds of Rafflesia patma Blume. Journal of Plant Development, 27, 19-32. https://doi.org/10.33628/jpd.2020.27.1.19

• Mursidawati, S., Wicaksono, A., & Teixeira da Silva, J. A. (2019). Development of the endophytic parasite, Rafflesia patma Blume, among host plant (Tetrastigma leucostaphylum (Dennst.) Alston) vascular cambium tissue. South African Journal of Botany, 123, 382-386. https://doi.org/10.1016/j.sajb.2019.03.028

• Mursidawati, S., Wicaksono, A., & Teixeira da Silva, J. A. (2020). Rafflesia patma Blume flower organs: histology of the epidermis and vascular structures, and a search for stomata. Planta, 251, 112. https://doi.org/10.1007/s00425-020-03402-5

• Nikolov, L. A., Staedler, Y. M., Manickam, S., Schönenberger, J., Endress, P. K., Kramer, E. M., & Davis, C. C. (2014a). Floral structure and development in Rafflesiaceae with emphasis on their exceptional gynoecia. American Journal of Botany, 101(2), 225-243. https://doi.org/10.3732/ajb.1400009

• Nikolov, L. A., Tomlinson, P. B., Manickam, S., Endress, P. K., Kramer, E. M., & Davis, C. C. (2014b). Holoparasitic Rafflesiaceae possess the most reduced endophytes and yet give rise to the world’s largest flowers. Annals of Botany, 114(2), 233-242. https://doi.org/10.1093/aob/mcu114

• Pace, M. R., Angyalossy, V., & Acevedo-rodr, P. (2018). Structure and ontogeny of successive cambia in Tetrastigma (Vitaceae), the host plants of Rafflesiaceae. Journal of Systematics and Evolution, 56(4), 394-400. https://doi.org/10.1111/jse.12303

• Pérez-de-Luque, A. (2013). Haustorium invasion into host tissues. In Parasitic Orobanchaceae (pp. 75-86). Springer. https://doi.org/10.1007/978-3-642-38146-1

• Razak, K. A., Che Hasan, R., Kamarudin, K. H., Haron, H. N., Sarip, S., Dziyauddin, R. A., & Fathi, S. (2015). Transroyal: Multi-inter-trans-disciplinary geo-biosphere research initiatives in the Royal Belum and Temengor Forest Complex (RBTFC) Gerik Perak. http://mjiit.utm.my/icsi2015/

• Rutherford, R. J. (1970). The anatomy and cytology of Pilostyles thurberi Gray (Rafflesiaceae). Aliso: A Journal of Systematic and Evolutionary Botany, 7(2), 263-288. https://doi.org/10.5642/aliso.19700702.13

• Susatya, A. (2020). The growth of flower bud, life history, and population structure of Rafflesia arnoldii (Rafflesiaceae) in Bengkulu, Sumatra, Indonesia. Biodiversitas Journal of Biological Diversity, 21(2), 792-798. https://doi.org/10.13057/biodiv/d210247

• Syamsurina, A. (2018). Taburan, fiziko-kimia tanah, anatomi dan mikroskopik Tetrastigma rafflesiae Planch. di Perak, Pahang, dan Kelantan [Distribution, soil physico-chemistry, anatomy and microscopy of Tetrastigma rafflesiae Planch. in Perak, Pahang, and Kelantan] [Unpublished Doctoral dissertation]. Universiti Kebangsaan Malaysia.

• Těšitel, J. (2016). Functional biology of parasitic plants: A review. Plant Ecology and Evolution, 149(1), 5-20. https://doi.org/10.5091/plecevo.2016.1097

• Tolivia, D., & Tolivia, J. (1987). Fasga: A new polychromatic method for simultaneous and differential staining of plant tissues. Journal of Microscopy, 148(1), 113-117. https://doi.org/10.1111/j.1365-2818.1987.tb02859.x

• Twyford, A. D. (2017). New insights into the population biology of endoparasitic Rafflesiaceae. American Journal of Botany, 104(10), 1433-1436. https://doi.org/10.3732/ajb.1700317

• Twyford, A. D. (2018). Parasitic plants. Current Biology, 28(16), R857-R859. https://doi.org/10.1016/j.cub.2018.06.030

• Wicaksono, A. (2015). Short Communication: Attempted callus induction of holoparasite Rafflesia patma Blume using primordial flower bud tissue. Nusantara Bioscience, 7(2), 96-101. https://doi.org/10.13057/nusbiosci/n070206