I've been growing lowii for years, and have multiple clones from multiple locations,
including Mts. Trus Madi, Kinabalu and Mulu. To date, I've found that this species,
apparently regardless of location, is *largely* unperturbed by overnight temps even as
high as 18 C, and some of my plants are quite large now. It is also a fairly easy
species to root, taking about three months to produce sufficient roots for planting.
However, I would not grow it as a true lowlander, nor would I grow it with overnight lows
of 18 C for any *real* length of time. It can tolerate it, but my suspicion, based upon careful
observation, is that it does not prefer such treatment, and it seems plausible that
such stress might weaken it enough for disease to take hold. After all, the altitudinal range
for this plant is 1600 to 2600 m, so it really is a true highlander.
Also, keep in mind that small plants are sometimes much more forgiving of high temperatures
than are adult specimens! So, if your temps are high, watch for a decline as plants get larger
and be prepared to act!