BIODIVERSITAS ISSN: 1412-033X Volume 17, Number 1, April 2016 E-ISSN: 2085-4722 Pages: 192-199 DOI: 10.13057/biodiv/d170128 Flowering, fruiting, seed germination and seedling growth of Macaranga gigantea DWI SUSANTO 1,♥ , DADDY RUCHIYAT 2 , MAMAN SUTISNA 2 , RUDIANTO AMIRTA 2 1 Department of Biology, Faculty of Mathematics and Natural Sciences, Mulawarman University. Jl. Barong Tongkok No. 4, Gunung Kelua, Samarinda Ulu, Samarinda-75123, East Kalimantan, Indonesia. Tel./Fax.: +62-541-749140, 749152, 749153,  email: susantodwiki@yahoo.com 2 Faculty of Forestry, Mulawarman University. Jl. Ki Hajar Dewantara, Kampus Gunung Kelua, Samarinda-75123, Indonesia Manuscript received: 31 December 2015. Revision accepted: 3 March 2016. Abstract. Susanto D, Ruchiyat D, Sutisna M, Amirta R. Flowering, fruiting, seed germination and seedling growth of Macaranga gigantea. Biodiversitas 17: 192-199. The stages of flower and fruit development of Macaranga gigantea, its seed germination behavior in nature and from fruit harvesting, as well as the process of raising its seedlings in the laboratory were studied to determine the potential for production of M. gigantea seedlings. Five reproductive trees of M. gigantea were chosen as sources of seed. To estimate natural germination rates, four sample plots of 1 x 1 m 2 in four cardinal directions below the crown of every tree were set up. In addition, dry and wet extraction processes were carried out to determine, which the more effective method for germination of M. gigantea seeds. The results showed that the time required from flower development to fruit ripening in M. gigantea flowers was 5-6 months. The flower buds initiated in the dry season (August 2011) and the fruits ripened in the rainy season (December 2011-January 2012). The seeds that fell under the parent tree germinated in approximately 24 days with an average seedling density of 75-267 per m 2 . The germination in laboratory showed that the percentage and the rate of germination of the seeds extracted through the wet extraction process were higher than those extracted through the dry extraction process. The highest rate of germination (65%) is by the combination of seeds extracted through wet extraction process and grown on compost media. The relative growth rate of seedlings planted on mushroom spawn waste media was the highest rate (0.36 0.42%), followed by those planted on compost media (0.150.09%), top soil media (0.100.04%) and sand media (0.100.07%). Keywords: Germination, Macaranga gigantea, pioneer species, seedling growth INTRODUCTION The giant mahang (Macaranga gigantea) has not been recognized as an important commodity with a high economic value. M. gigantea wood is light, soft and flimsy that it is not good for construction wood. However, Amirta (2010) reported that enzymatic hydrolysis process of M. gigantea wood produces the highest reducing sugar content (82.47% based on the weight of resultant pulp) compared to other types of fast growing woody species such as Paraserianthes falcatria and Acacia mangium and this plant has the potential to be used as raw material for bioethanol in the near future. Liquid bioethanol generated from wood is long lasting providing that the forest where it grows is preserved (sustainable) and it does not affect the production of food and the increasing price of food materials. M. gigantea has not yet been cultivated and information about the stages of its flower and fruit development, seed germination in nature, as well as the process of raising its seedlings is still very limited. In order to have M. gigantea seedlings ready for cultivation, a source of seeds harvested from physiologically mature fruits is needed. Seed extraction is required to remove the seeds from other parts of the fruit (skin, flesh, wings, stalks), and if the seeds are not appropriately extracted, their germination viability will decrease. In nature, M. gigantea plant is abundant in open mixed dipterocarp forests after extensive disturbances such as wood harvesting, forest fires, and shifting cultivation (Lawrence 2001; Silk et al. 2003; Lawrence 2005; Eichhorn 2006; Silk et al. 2008). After a great forest fire in East Kalimantan (1982-1983), M. gigantea and M. triloba simultaneously spread over and covered the canopy gaps of the destroyed forest, believed that seeds of M. gigantea and M. triloba might be buried in the soil before the forest fires and then they germinated immediately after the fires. However, Kiyono and Hastaniah (1997) reported that a careful observation indicated that Austroeupatorium inulifolium and some of wild bananas (Musa sp.) had been growing before the seedlings of M. gigantea and M. triloba grew and spread over the forest. They speculate that there were a considerable number of M. gigantea and M. triloba seed-trees that survived. Seeds of M. gigantea were reported to have low water content of 8.23% and the seeds with low water content were commonly orthodox (Suita and Nurhasybi 2009). M. gigantea seeds resulting from dry extraction from mature fruits have low germination rates of 2-10%, but soaking the seeds into a solution of 0.2% potassium nitrate for 20 minutes before spreading on sand media can increase germination rates of seeds up to 20% (Mindawati et al. 2010). It is necessary to conduct a study on the stages of flower and fruit development of M. gigantea, its seed germination behavior in nature, its seed germination rates from the fruit harvesting, as well as the process of raising