Monanthocitrus paludosa (Lauterb.) Stone (1985: 217). Citrus paludosa Lauterbach (1918: 263). Type:— PAPUA NEW GUINEA. East Sepik Province: Sepik River (mouth), swampy coastal forest with sago palms and rattans, 1 May 1912, Ledermann 7173 (holotype B, lost; isotype K, fide Stone 1985). Additional specimens examined: — PAPUA NEW GUINEA. East Sepik Province: April River, lower slopes of Kamelsrücken, opposite Natawe, swampy forest, 4°35'S, 142°33'E, 70 m, 27 November 2007, Takeuchi, Towati & Ama 22418 B (A!, CANB!, LAE!); Sepik River, downstream from Aprilfluss junction, alluvial swamp forest, 4°15'S, 142°30'E, 40 m, 29 November 2007, Takeuchi, Towati & Ama 22419 B (A!, BO!, CANB!, L!, LAE!). Previously found only by the Kaiserin-Augusta-Fluss Expedition, Monanthocitrus paludosa occurs in scattered populations along the Sepik channel, primarily in backswamps and scrolls bordering the riverbed meanders. These habitats are understandably among PNG's least explored places because of an intrinsic abundance of malarial mosquitos, leeches, crocodiles, and snakes. Given its prolonged absence from the scientific record, M. paludosa is an ironically common species of the Sepik wetland. The taxon's poor representation in world herbaria is a result of historical collecting patterns rather than biological rarity. New Guinea Aurantioideae were not previously regarded as myrmecophytic but the latest specimens of Monanthocitrus paludosa are clearly ant-inhabited. Although lacking the juice-filled vesicles of a true citrus, the remarkably orange-like fruits are sweet-tasting and somewhat like an apple (Fig. 6).