Both of them are endemic to Sumatra. _N.rhombicaulis_ can be distinguished
by its stem which is angular (rhomboid in cross section). _N.spectabilis_
has large slender upper pitchers which are unusually hairy for a Sumatran
_Nepenthes_. I think they have not been confused with other species, and no
other popular name is known, yet.
>Actually, I may as well go for broke here. What can be
>said about N. Gymnamphora, N. Hirsuta, and N. Thorellii?
_N.gymnamphora_ (Sumatra and Java, syn.:_N.pectinata_ p.p.) is easily
distinguishable by its ovoid (really egg-shaped!) lower pitchers in compact
rosettes with small leaves.
_N.hirsuta_ (Borneo and adjacent islands, syn.:_N.neglecta_,
_N.leptochila_, maybe also _N.mollis_. _N.macrovulgaris_ is very closely
related) is quite unspectacular but very hairy with long, brown hairs.
These hairs may be sparse or absent on some parts.
_N.thorelii_ (Indochina) has narrow leaves with wings running down the stem
for some distance. The lower pitchers are some way reminiscent of the lower
pitchers of _N.rafflesiana_ but smaller and without the diagnostic vaulted
lid. The lid is provided with homogeneously distributed round glands
beneath.
Kind regards
Jan