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| Disepalum rawagambut Randi, D.C.Thomas & Wijedasa, in Randi, Wijedasa & Thomas, 2022. photos by A. Randi. facebook.com/RandiAgusti |
Disepalum Hooker (1860: 156) is a small genus of nine species of trees and shrubs distributed from southern China to western Malesia (Peninsular Malaysia, Sumatra and Borneo; Johnson 1989, Li et al. 2015, Li et al. 2017). The genus has characteristic carpophores derived from receptacle tissue, whereas the vast majority of Annonaceae genera have monocarp stalks derived from carpel tissue (Van Setten & Koek-Noorman 1992). Johnson (1989) provided detailed species descriptions in his revision of the genus, and the phylogenetic relationships, intergeneric classification, morphological character distribution and evolution and historical biogeography of Disepalum were studied by Li et al. (2015, 2017). Phylogenetic analyses placed Disepalum in tribe Annoneae (Annonaceae) and indicate a sister relationship with the Neotropical genus Asimina Adanson (1763: 365; Erkens et al. 2014; Li et al. 2015).
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Three of the nine Disepalum species have been reported from the Indonesian island of Sumatra (Johnson 1989, Li et al. 2015, Li et al. 2017, POWO 2019), all subgenus Disepalum, and two of these endemic (Table 1). This new fourth Sumatran species has flowers with two sepals, four connate petals and persistent sepals in fruit, which clearly place it in D. subgen. Disepalum (Johnson 1989, Li et al. 2015). Terminology largely follows Beentje (2010). We provisionally assess the conservation status of the new species following IUCN criteria (IUCN 2019).
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| Disepalum rawagambut Randi, D.C.Thomas & Wijedasa. A. Flower with pedicel (side view). B. Flower (top view). C. Flower (side view). D. Infructescence. E. Carpophore and monocarp.F. Immature monocarp (longitudinal section). G. Mature monocarp (longitudinal section) and seeds. All photos by A. Randi from the holotype (Randi GB-035) |
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| Disepalum rawagambut Randi, D.C.Thomas & Wijedasa. A. Trunk and stilt roots on old tree. B. Twig with flowers and infructescence. C. Close-up of twig. D. Adaxial surface (upper) and abaxial surface (below) of leaves. All photos by A. Randi from the holotype (Randi GB-035). |
Disepalum rawagambut Randi, D.C.Thomas & Wijedasa, sp. nov.
Disepalum rawagambut has flowers with two sepals and four relatively short, spatulate corolla lobes that are thickened in the distal part with blunt apices similar to those of D. anomalum (Borneo) and D. longipes (Malay Peninsula, Sumatra). The new species can be differentiated by a combination of characters including its habit, large sepals, smaller corolla lobes and larger fruit (larger torus, longer carpophores, and larger monocarps; Table 1).
Etymology:— The species epithet refers to the specific habitat of the new species in Bahasa Indonesia: rawa gambut (peat swamp).
Agusti Randi, Lahiru S. Wijedasa and Daniel C. Thomas. 2022. Disepalum rawagambut (Annonaceae), A New Tree Species from Peat Swamp Forest of Sumatra, Indonesia. Phytotaxa. 530(1); 121-126. DOI: 10.11646/phytotaxa.530.1.14
Keywords: Annonaceae, Disepalum rawagambut, peat swamp, rawa gambut, Sumatra, plant taxonomy, Magnoliids
