Hydnophytum kajewskii (above), a species of ant-plant from Bougainville island, has the most elaborate tuber structure known, and must rank as one of the most elaborate and bizarre vegetative structures in the entire plant kingdom. The boat-shaped tuber, which grows up to 25 cm in length, and 12 cm in width, looses its symmetry with age. The tuber-cavities each open by a pair of large, lipped entrance holes which are aligned along the upper edge of the tuber. The tuber may contain ants, or a range of other invertebrates, from spiders, scorpions, cockroaches and myriopods. New cavities are added one at a time to the apex of the tuber.

Project Background

Hydnophytum is the largest of the five genera of ‘ant-plants’ in the Rubiaceae. These plants are almost exclusively epiphytic, and develop chambered tubers at the base of their stems, which act as homes to ants or other creatures – a remarkable symbiotic relationship in which the ant colony gets a home, and leaves behind detritus that helps to feed the plant.

The other four genera (Myrmecodia, Myrmephytum, Squamellaria and Anthorrhiza) have been revised (Huxley & Jebb, 1991b, 1991c and 1993; Jebb, 1991b, 1993). Of the 108 species of Hydnophytum that have been published, 33 have been retained in this revision, and a further 22 species are described as new. Eleven species remain known from their holotype alone, a problem with many New Guinea centred genera. Six species are inadequately known, either through loss of the type, or paucity of material, and these are retained as ‘little known species’. Five names are excluded from the genus. Fifty-five species are therefore recognised, of which 22 are described as new. Forty-four species are found in New Guinea, or its offshore islands, and of these, 42 are endemic. Two species are found in the Fijian islands, one in Vanuatu, three in the Solomon islands, five in Indonesia, and two in Australia. The Royal Society of London gave a grant towards preparing drawings of all the species, and these were done by Rosemary Wise of Oxford.

 

The diversity of tuber structure within Hydnophytum is in marked contrast to that seen in the other genera, and suggests that while the other genera are certainly monophyletic, Hydnophytum is a paraphyletic grouping (Jebb 1991a).

References

Huxley, C.R. & M.H.P. Jebb. 1990. New taxa in the myrmecophilous  Psychotrieae (Rubiaceae). Bull. Jard. Bot. Nat. Belg. 60: 420–421.
Huxley, C.R. & M.H.P. Jebb. 1991a. The tuberous epiphytes of the Rubiaceae 1: A new subtribe – The Hydnophytinae. Blumea 36: 1– 20.
Huxley, C.R. & M.H.P. Jebb. 1991b. The tuberous epiphytes of the Rubiaceae 2: The new genus Anthorrhiza. Blumea 36: 21–41.
Huxley, C.R. & M.H.P. Jebb. 1991c. The tuberous epiphytes of the Rubiaceae 3: A revision of Myrmephytum to include Myrmedoma. Blumea 36: 43–52.
Huxley, C.R. & M.H.P. Jebb. 1993. The tuberous epiphytes of the Rubiaceae 5: A revision of Myrmecodia. Blumea 37:271–334.
Jebb, M.H.P. 1991a. Cavity structure and function in the tuberous Rubiaceae. In C.R.Huxley & D.F.Cutler, Ant-plant Interactions: 374 –389. Oxford Univ. Press.
Jebb, M.H.P. 1991b. The tuberous epiphytes of the Rubiaceae 4: A revision of Squamellaria. Blumea 36: 53–61.
Jebb, M.H.P. 1993. Anthorrhiza camilla — A new species of Rubiaceous ant–plant. Blumea 37: 341–344.


CHECKLIST of the rubiaceous Ant-Plants (Dec 2018)

Anthorrhiza C.R.Huxley & Jebb
Anthorrhiza areolata
C.R.Huxley & Jebb
Anthorrhiza bracteosa C.R.Huxley & Jebb
Anthorrhiza caerulea C.R.Huxley & Jebb
Anthorrhiza camilla Jebb
Anthorrhiza chrysacantha C.R.Huxley & Jebb
Anthorrhiza echinella C.R.Huxley & Jebb
Anthorrhiza mitis C.R.Huxley & Jebb
Anthorrhiza recurvispina C.R.Huxley & Jebb
Anthorrhiza stevensii C.R.Huxley & Jebb

Hydnophytum Jack
Hydnophytum acuminicalyx
Jebb & C.R.Huxley
Hydnophytum albertisii Becc.
Hydnophytum alboviride Merr. & L.M.Perry
Syn: Hydnophytum crassicaule P.Royen
Syn: Hydnophytum vaccinifolium P.Royen
Hydnophytum angustifolium Merr.
Hydnophytum archboldianum Merr. & L.M.Perry
Hydnophytum bracteatum Valeton
Hydnophytum buxifolium Merr. & L.M.Perry
Hydnophytum caminiferum Wistuba, U.Zimm., Gronem. & Marwinski
Hydnophytum confertifolium Merr. & L.M.Perry
Hydnophytum cordifolium Valeton
Hydnophytum dauloense Jebb & C.R.Huxley
Hydnophytum davisii Jebb & C.R.Huxley
Hydnophytum decipiens Merr. & L.M.Perry
Hydnophytum dentrecastense Jebb & C.R.Huxley
Hydnophytum ellipticum Merr. & L.M.Perry
Hydnophytum ferrugineum P.I.Forst.
Hydnophytum formicarum Jack; Syn: Lasiostoma formicarum (Jack) Spreng.
Syn: Hydnophytum amboinense Becc.
Syn: Hydnophytum andamanense Becc.
Syn: Hydnophytum blumei Becc.
Syn: Hydnophytum borneense Becc.
Syn: Hydnophytum coriaceum Becc.
Syn: Hydnophytum formicarum Kurz
Syn: Hydnophytum gaudichaudii Becc.
Syn: Hydnophytum inerme (Gaudich.) Bremek.; Myrmecodia inermis Gaudich.
Syn: Hydnophytum intermedium Elmer
Syn: Hydnophytum leytense Merr.
Syn: Hydnophytum membranaceum Merr.
Syn: Hydnophytum mindorense Merr.
Syn: Hydnophytum montanum Blume
Syn: Hydnophytum montanum Scheff.
Syn: Hydnophytum nitidum Merr.
Syn: Hydnophytum orbiculatum Elmer
Syn: Hydnophytum selebicum Becc.
Syn: Hydnophytum sumatranum Becc.
Hydnophytum fusiforme Jebb & C.R.Huxley
Hydnophytum grandiflorum Becc.
Syn: Myrmecodia vitiensis Gaudich. nom. nud.
Syn: Squamellaria jebbiana Chomicki
Hydnophytum grandifolium Valeton
Hydnophytum hailans Jebb & C.R.Huxley
Hydnophytum hellwigii Warb.
Syn: Hydnophytum parvifolium Valeton
Syn: Hydnophytum punamense Lauterb.
Hydnophytum heterophyllum Merr. & L.M.Perry
Hydnophytum kebarense Jebb & C.R.Huxley
Hydnophytum lauterbachii Valeton
Hydnophytum linearifolium Valeton
Syn: Hydnophytum dolichophyllum Valeton
Hydnophytum longiflorum A.Gray
Syn: Hydnophytum horneanum Becc.; Syn: Hydnophytum borneanum sphalm.
Syn: Hydnophytum tenuiflorum Becc.; Squamellaria tenuiflora (Becc.) Chomicki
Syn: Hydnophytum wilkinsonii Horne ex Baker; Squamellaria wilkinosii (Horne ex Baker) Chomicki
Hydnophytum lucidulum Valeton
Hydnophytum magnifolium Merr. & L.M.Perry
Hydnophytum magnirubrum Jebb & C.R.Huxley
Hydnophytum mamberamoense Jebb & C.R.Huxley
Hydnophytum mayuense Jebb & C.R.Huxley
Hydnophytum microphyllum Becc.
Hydnophytum minirubrum Jebb & C.R.Huxley
Hydnophytum morotaiense Jebb & C.R.Huxley
Hydnophytum moseleyanum Becc.
Syn: Hydnophytum agatifolium Valeton
Syn: Hydnophytum brachycladum Merr.
Syn: Hydnophytum brassii S.Moore
Syn: Hydnophytum camporum S.Moore
Syn: Hydnophytum capitatum Valeton
Syn: Hydnophytum crassifolium Becc.
Syn: Hydnophytum cuneatum Valeton
Syn: Hydnophytum forbesii Hook.f.
Syn: Hydnophytum laurifolium Warb.
Syn: Hydnophytum longistylum Becc.
Syn: Hydnophytum loranthifolium (Benth.) Becc.; Lasiostoma loranthifolium Benth.
Syn: Hydnophytum macrophyllum Warb.
Syn: Hydnophytum mindanaense Elmer
Syn: Hydnophytum moseleyanum var. teysmannii Becc.
Syn: Hydnophytum oblongum (Benth.) Becc.; Lasiostoma oblongum Benth.
Syn: Hydnophytum papuanum Becc.
Syn: Hydnophytum papuanum Becc.
Syn: Hydnophytum philippinense Becc.
Syn: Hydnophytum robustum Rechinger
Syn: Hydnophytum stewartii Fosberg
Syn: Hydnophytum subfalcifolium Valeton
Syn: Hydnophytum subrotundum Valeton
Hydnophytum multituberosum Jebb & C.R.Huxley
Hydnophytum myrtifolium Merr. & L.M.Perry
Hydnophytum orichalcum Jebb & C.R.Huxley
Hydnophytum ovatum Miq.
Hydnophytum pauper Valeton ex Jebb & C.R.Huxley
Hydnophytum petiolatum Becc.
Hydnophytum petiolatum var. argentatum Jebb & C.R.Huxley
Hydnophytum petiolatum var. auridemens Jebb & C.R.Huxley
Hydnophytum petiolatum var. contortum (Merr. & L.M.Perry) Jebb & C.R.Huxley; Hydnophytum contortum Merr. & L.M.Perry
Hydnophytum petiolatum var. lacum Jebb & C.R.Huxley
Hydnophytum petiolatum var. ledermannii (Valeton) Jebb & C.R.Huxley; Hydnophytum ledermannii Valeton
Hydnophytum petiolatum var. nigrescens (Merr. & L.M.Perry) Jebb & C.R.Huxley; Hydnophytum nigrescens Merr. & L.M.Perry
Hydnophytum petiolatum var. petiolatum Becc.
Syn: Hydnophytum kochii Valeton
Hydnophytum puffii Y.W.Low, Sugau & K.M.Wong
Hydnophytum radicans Becc.
Syn: Hydnophytum albense Valeton
Syn: Hydnophytum amplifolium S.Moore
Syn: Hydnophytum keiense Becc.
Syn: Hydnophytum kejense Becc.
Syn: Hydnophytum kelelense Valeton
Syn: Hydnophytum montis-kani Valeton
Syn: Hydnophytum normale Becc.
Syn: Hydnophytum simplex Becc.
Syn: Hydnophytum subnormale K.Schum.
Hydnophytum ramispinum Merr. & L.M.Perry
Hydnophytum reevii Jebb & C.R.Huxley
Hydnophytum spathulatum Valeton
Hydnophytum stenophyllum Valeton
Hydnophytum subsessile Valeton
Hydnophytum terrestris Jebb & C.R.Huxley
Hydnophytum tetrapterum Becc.
Hydnophytum tortuosum Becc.
Hydnophytum trichomanes Jebb & C.R.Huxley
Hydnophytum valetonii Jebb & C.R.Huxley
Hydnophytum virgatum Valeton
Hydnophytum vitis-idaea Merr. & L.M.Perry
Hydnophytum zippelianum Becc.

Myrmecodia Jack
Myrmecodia alata
Becc.
Syn: Myrmecodia aruensis Becc.
Syn: Myrmecodia prolifera Merr. & L.M.Perry
Myrmecodia albertisii Becc.
Syn: Myrmecodia albertisii Becc.
Myrmecodia albertisii subsp. incompta C.R.Huxley & Jebb
Myrmecodia albertisii subsp. valida C.R.Huxley & Jebb
Myrmecodia angustifolia Valeton
Myrmecodia archboldiana Merr. & L.M.Perry
Myrmecodia aureospina C.R.Huxley & Jebb
Myrmecodia brassii Merr. & L.M.Perry
Myrmecodia decasperma Valeton
Myrmecodia erinacea Becc.
Myrmecodia ferox C.R.Huxley & Jebb
Myrmecodia gracilispina C.R.Huxley & Jebb
Myrmecodia horrida C.R.Huxley & Jebb
Myrmecodia jobiensis Becc.
Myrmecodia kutubuensis C.R.Huxley & Jebb
Myrmecodia lamii Merr. & L.M.Perry
Myrmecodia longifolia Valeton
Myrmecodia longissima Valeton
Myrmecodia melanacantha C.R.Huxley & Jebb
Myrmecodia oblongata Valeton
Myrmecodia oksapminensis C.R.Huxley & Jebb
Myrmecodia paradoxa C.R.Huxley & Jebb
Myrmecodia pendens Merr. & L.M.Perry
Myrmecodia platytyrea Becc.
Myrmecodia platytyrea Becc.
Myrmecodia platytyrea subsp. antoinii (Becc.) C.R.Huxley & Jebb
Syn: Myrmecodia antoinei Becc.
Myrmecodia pteroaspida C.R.Huxley & Jebb
Syn: Myrmecodia pteroaspida C.R.Huxley & Jebb
Myrmecodia schlechteri Valeton
Myrmecodia schlechteri subsp. eraveensis C.R.Huxley & Jebb
Myrmecodia schlechteri subsp. kopiagoensis C.R.Huxley & Jebb
Myrmecodia schlechteri subsp. pendula (Merr. & L.M.Perry) C.R.Huxley & Jebb; Myrmecodia pendula Merr. & L.M.Perry
Myrmecodia schlechteri var. longispina (Valeton) C.R.Huxley & Jebb; Myrmecodia longispina Valeton
Myrmecodia sterrophylla Merr. & L.M.Perry
Myrmecodia tuberosa Jack; &&Lasiostoma tuberosum (Jack) Spreng.
Syn: Myrmecodia amboinensis Becc.
Syn: Myrmecodia bullosa Becc.
Syn: Myrmecodia dahlia K.Schum.
Syn: Myrmecodia echinata Antoine
Syn: Myrmecodia echinata F.Muell.
Syn: Myrmecodia echinata Gaudich.
Syn: Myrmecodia echinata Miq.
Syn: Myrmecodia hispida A.Rich.
Syn: Myrmecodia inermis Benth. & Hook.f.
Syn: Myrmecodia inermis DC.
Syn: Myrmecodia lanceolata Valeton
Syn: Myrmecodia muelleri Becc.
Syn: Myrmecodia oninensis Becc.
Syn: Myrmecodia paucispina Valeton
Syn: Myrmecodia peekelii Valeton
Syn: Myrmecodia pentasperma K.Schum.
Syn: Myrmecodia pulvinata Becc.
Syn: Myrmecodia salomonensis Becc.
Syn: Myrmecodia tuberose Becc. ex Treub
Syn: Myrmecodia vivipara Warb.

Myrmephytum Becc.

Myrmephytum arfakianum (Becc.) C.R.Huxley & Jebb; Myrmedoma arfakiana Becc.
Myrmephytum moniliforme C.R.Huxley & Jebb
Myrmephytum naumannii (Warb.) C.R.Huxley & Jebb; Myrmedoma naumannii Warb.
Myrmephytum selebicum (Becc.) Becc.; Myrmecodia selebica Becc.

Squamellaria Becc.

Squamellaria grayi Chomicki & Wistuba
Squamellaria guppyana (Becc.) Chomicki; Hydnophytum guppyanum Becc.
Syn: Hydnophytum hahlii Rechinger
Syn: Hydnophytum longipes Merr. & L.M.Perry
Squamellaria huxleyana Chomicki
Squamellaria imberbis Becc.
Syn: Hydnophytum wilsonii Horne ex Baker
Squamellaria kajewskii (Merr. & L.M.Perry) Chomicki; Hydnophytum kajewskii Merr. & L.M.Perry
Squamellaria major A.C.Sm.
Squamellaria thekii Jebb
Squamellaria vanuatuensis Jebb & C.R.Huxley in Chomicki and S.S.Renner

Excluded species
Non Hydnophytinae?
  Syn:  Hydnophytum lanceolatum Miq.
Psychotria dipteropoda K.Schum. & Lauterb; Hydnophytum dipteropodum (Lauterb. & K.Schum.) Valeton
Syn: Hydnophytum diplopodum Valeton
Psychotria leptothyrsa Miq.
Syn: Hydnophytum beccarii K.Schum.
Scyphiphora hydrophyllacea C.F. Gaertn.
Syn: Hydnophytum costatum Drake