Taxonomy
The Philippines is the centre of diversity for the genusRafflesia with 16 species recognized, including the species we describe here: Rafflesia balatociana. Nine of these occur on Luzon Island. The taxonomy of the Rafflesia of Luzon has been confused and in a state of flux, despite nearly a century and a half of documented botanical exploration in the region. For example R. banahawensis Madulid, Villariba–Tolentino & Agoo (Madulid et al. 2008) [as R. philippensis in Barcelona et al.2009b; Blanco 1845] in the Banahaw–San Cristobal Protected Landscape (Barcelona et al. 2008b; Madulid et al. 2006; Pelseret al. 2013) and R. panchoana Madulid, Buot & Agoo in the Mount Makiling Forest Reserve (Madulid et al. 2007, 2012) [asR. manillana in Fernando & Ong 2005a; as R. lagascae in Barcelona et al. 2009c, 2011; Pelser et al. 2013] were both overlooked until recently, and synonymised under R. manillana , a distinct species from Basey, Samar Island (Madulid & Agoo 2007). More recently, R. banaoana Malabrigo, was first described in 2010 (Malabrigo 2010), synonymized with R. leonardi Barcelona & Pelser (Barcelona et al. 2011), and then recently reinstated (Tobias et al. 2023). Traditionally, Rafflesiaspp. in the Philippines have been described with emphasis on various diagnostic characters including habit, flower color and size, wart ornamentations on the perigone lobes, color and surface of diaphragm, diaphragm aperture, types of ramenta and number of anthers. Recently, we emphasized the importance of stable yet hitherto neglected features such as the stigmatic fascia surface, disk shape, process structure, annulus interior and exterior distinction, and ovary shape (Tobias et al . 2023). Meijer (1997), in his monograph of the genus, also highlighted the significance of annulus structure in classifying Rafflesia,as well as their ramenta. Since then, authors across Southeast Asia have placed varying emphasis on different characters, leading to inconsistent descriptions that are challenging to compare objectively. Some of these – specially size- and colour-related, are continuously variable, so must be considered alongside more stable characters, such as the shape of the processes and their apical indumentum, disk undersurface, rim extension and margin of the disk, structure of the anther attachment to the sulci, structure of the lamella and grooves on the annulus interior and shape of the ovary. Accordingly, R. balatociana should be distinguished by its combination of stable characters, especially the double-dentate disk rim and the strap-shaped lacuna on the annulus interior.
Key to the Rafflesia species of the Cordillera Central
1. Flower large, typically 35-50 cm across, reddish–orange with paler warts; disk weakly domed ………………..………………..…………………………………………………..…