The term "umbrella" is probably not very appropriate, and I think
"tuba" shaped is a better description (are we talking about the same
thing?). When these pitchers develop, the "normal" slit present in
the _Heliamphora_ pitcher is not present as a slit, it is wide open.
Hence water just runs straight out and does not accumulate as in a
healthy pitcher. Clear as mud??
--Cheers Terry