Hydnophytum
Introduction '''''Hydnophytum''''' is a genus of epiphytic myrmecophytes (ant plants) native to Southeast Asia, the Pacific region and also extending into Queensland in northern Australia. The name is derived from the Ancient Greek ''hydnon'' "tuber", and ''phyton'' "plant", after their appearance with their swollen succulent stems. The species grow in tree branches and on trunks. Like the related genus ''Myrmecodia'', they are known as antplants or ant-house plants. The type species is ''Hydnophytum formicarum'' from the Philippines. The genus contains 55 species, of which 44 are found in and around the island of New Guinea. Many are poorly known, with 11 known only from the holotype.They form a symbiotic relationship with ants. Ant plants provide habitats for ant colonies high up into the forest canopy, protecting them from the elements and also predators because of the spines. Hollow, smooth-walled tunnels form within the caudex with external entrance holes, providing an above-ground home for ant colonies. Ants likewise provide defense for the plant and prevent tissue damage, swarming to defend their home if disturbed. Ant colonies also provide nutrients to the plants by leaving wastes within the tunnels inside the caudex. Special glands lining the tunnels then absorb nutriment for the plant. This symbiosis allows the plants to effectively gather nutrients (via the ants) from a much larger area than the roots ever could cover.These plants can be grown in cultivation without the ant species being present. Two species seen occasionally in cultivation are ''Hydnophytum ferrugineum'' from the McIlwraith Ranges east of Coen on the Cape York Peninsula, and ''H. moseleyanum'', also from Cape York. The former has a spiny swollen trunk while the latter has a smooth one. ''Hydnophytum'' is one of five ant-plant genera in the family Rubiaceae, the others being ''Anthorrhiza'', ''Myrmecodia'', ''Myrmephytum'', and ''Squamellaria''.
Species The following list, which includes more than 90 species, is based on The Plant List and likely includes many synonyms. Matthew Jebb and Camilla Huxley recognise only 55 species in the genus. *''Hydnophytum agatifolium'' Valeton*''Hydnophytum albense'' Valeton*''Hydnophytum albertisii'' Becc. *''Hydnophytum alboviride'' Merr. & L.M.Perry*''Hydnophytum amboinense'' Becc. *''Hydnophytum amplifolium'' S.Moore*''Hydnophytum andamanense'' Becc. *''Hydnophytum angustifolium'' Merr. *''Hydnophytum archboldianum'' Merr. & L.M.Perry*''Hydnophytum borneanum'' Becc. *''Hydnophytum brachycladum'' Merr. *''Hydnophytum bracteatum'' Valeton*''Hydnophytum brassii'' S.Moore*''Hydnophytum buxifolium'' Merr. & L.M.Perry*''Hydnophytum caminiferum'' Wistuba, U.Zimm., Gronem. & Marwinski*''Hydnophytum camporum'' S.Moore*''Hydnophytum capitatum'' Valeton*''Hydnophytum confertifolium'' Merr. & L.M.Perry*''Hydnophytum contortum'' Merr. & L.M.Perry*''Hydnophytum cordifolium'' Valeton*''Hydnophytum coriaceum'' Becc. *''Hydnophytum costatum'' Drake*''Hydnophytum crassicaule'' P.Royen*''Hydnophytum crassifolium'' Becc. *''Hydnophytum cuneatum'' Valeton*''Hydnophytum decipiens'' Merr. & L.M.Perry*''Hydnophytum dipteropodum'' (K.Schum. & Lauterb.) Valeton*''Hydnophytum dolichophyllum'' Valeton*''Hydnophytum ellipticum'' Merr. & L.M.Perry*''Hydnophytum ferrugineum'' P.I.Forst. *''Hydnophytum forbesii'' Hook.f. *''Hydnophytum formicarum'' Jack*''Hydnophytum grandiflorum'' Becc. *''Hydnophytum grandifolium'' Valeton*''Hydnophytum guppyanum'' Becc. *''Hydnophytum hahlii'' Rech. *''Hydnophytum hellwigii'' Warb. *''Hydnophytum heterophyllum'' Merr. & L.M.Perry*''Hydnophytum inerme'' (Gaudich.) Bremek. *''Hydnophytum intermedium'' Elmer*''Hydnophytum kajewskii'' Merr. & L.M.Perry*''Hydnophytum kejense'' Becc. *''Hydnophytum kelelense'' Valeton*''Hydnophytum kochii'' Valeton*''Hydnophytum lanceolatum'' Miq. *''Hydnophytum laurifolium'' Warb. *''Hydnophytum lauterbachii'' Valeton*''Hydnophytum ledermannii'' Valeton*''Hydnophytum leytense'' Merr. *''Hydnophytum linearifolium'' Valeton*''Hydnophytum longiflorum'' A.Gray*''Hydnophytum longipes'' Merr. & L.M.Perry*''Hydnophytum longistylum'' Becc. *''Hydnophytum loranthifolium'' (Benth.) Becc. *''Hydnophytum lucidulum'' Valeton*''Hydnophytum macrophyllum'' Warb. *''Hydnophytum magnifolium'' Merr. & L.M.Perry*''Hydnophytum membranaceum'' Merr. *''Hydnophytum microphyllum'' Becc. *''Hydnophytum mindanaense'' Elmer*''Hydnophytum mindorense'' Merr. *''Hydnophytum montis-kani'' Valeton*''Hydnophytum moseleyanum'' Becc. *''Hydnophytum myrtifolium'' Merr. & L.M.Perry*''Hydnophytum nigrescens'' Merr. & L.M.Perry*''Hydnophytum nitidum'' Merr. *''Hydnophytum normale'' Becc. *''Hydnophytum oblongum'' (Benth.) Becc. *''Hydnophytum orbiculatum'' Elmer*''Hydnophytum ovatum'' Miq. *''Hydnophytum papuanum'' Becc. *''Hydnophytum parvifolium'' Valeton*''Hydnophytum petiolatum'' Becc. *''Hydnophytum philippinense'' Becc. *''Hydnophytum punamense'' Lauterb. *''Hydnophytum radicans'' Becc. *''Hydnophytum ramispinum'' Merr. & L.M.Perry*''Hydnophytum robustum'' Rech. *''Hydnophytum selebicum'' Becc. *''Hydnophytum simplex'' Becc. *''Hydnophytum spathulatum'' Valeton*''Hydnophytum stenophyllum'' Valeton*''Hydnophytum stewartii'' Fosberg*''Hydnophytum subfalcifolium'' Valeton*''Hydnophytum subnormale'' K.Schum. *''Hydnophytum subrotundum'' Valeton*''Hydnophytum subsessile'' Valeton*''Hydnophytum sumatranum'' Becc. *''Hydnophytum tetrapterum'' Becc. *''Hydnophytum tortuosum'' Becc. *''Hydnophytum vaccinifolium'' P.Royen*''Hydnophytum virgatum'' Valeton*''Hydnophytum vitis-idaea'' Merr. & L.M.Perry*''Hydnophytum wilkinsonii'' Horne ''ex'' Baker*''Hydnophytum zippelianum'' Becc.
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