Hydnophytum stenophyllum

[Derrick]

H. stenophyllum Val. (Theodoric Valeton) Just's botanischer jahresbericht. Systematisch geordnetes repertorium der botanischen literatur aller länder, vol.61, p140, (1927).
 (Bot. Jahrb. Syst.), not yet digitised. Update. Jebb & C. R. Huxley, in The tuberous epiphytes of the Rubiaceae 7: a revision of the genus Hydnophytum, Blumea 64, p85, (2019.) 
A member of their Uncertain and Little Known Species. Type, Schlechter 18173 (1908) Jebb & C. R. Huxley note “K not seen, presumed lost” Papua New Guinea, 
Madang Province, Huon Peninsula, Finisterre Mountains at 300m (984 ft.) Yet here it is. http://apps.kew.org/herbcat/getImage.do?imageBarcode=K000761951 

This specimen has distinct, long and somewhat narrow leaves.

 

Merr. & L.M. Perry note when referring to H. ramispinum. “In leaf-size and flower, this species (i.e. ramispinum) is near Hydnophytum stenophyllum Val. and 
H. punamense Lauterb. In both the latter species the leaves are either attenuate-acute or acute, and in neither is there any mention of the furfuraceous character of the young bark.
Unfortunately, many of the species have no indication of the characters of the tuberous base. (Elmer Drew Merrill & Lily May Perry) Journal Arnold Arboretum Vol 26, pp23, (1945) 
(J. Arnold Arbor.)

http://www.biodiversitylibrary.org/page/8443412#page/28/mode/1up