Hi John,
During the time I've been in Sarawak (going on 4 months), I've
noticed a gradual increase in the number of species in flower to
a peak around late May. When I first arrived, it was apparent
from the old, dried inflorescences (several internodes below the
growing tip) that many species of Nepenthes hadn't flowered for
quite awhile. Possibly these dried stalks were from the same
time last year. Right now the flowers of most species are in
decline and seed pods are swelling.
We are very close to the equator but it seems that the slightly
increasing daylength has corresponded with the flowering cycles.
Tom Kahl's observations appear to aggree with this as well.
Perhaps a field trip now to Nepenthes south of the equator would
provide some interesting observations. I'm sure there are other
factors besides photperiod which are involved, though.
Also, it appears that in the case of lowland species, hot dry
weather induces the ripe seed capsules to burst. I have observed
numerous ripe seed capsules which have remained unopened during
wet, rainy weather. However after a few hot dry days, the pods
split (probably due to dessication) and the seed is released.
This would seem advantageous to the dispersal of seed since those
released during a rainstorm would be washed into the rivers
rather than being scattered by wind to more suitable habitats.
Thus it would make sense for plants to flower at the very
beginning of the dry season.
Best wishes,
Ch'ien