Question: what does it mean when the leaves change dark brownish and fall off?
Answer: Columnea could lose foliage this way if kept in too much direct sun, if overwatered, or if the air is too dry. It likes bright but indirect light, high humidity, and moist but not sopping wet soil.
Q&A Library Searching Tips
When singular and plural spellings differ, as in peony and peonies, try both.