Kalanchoe

K. longiflora K. longiflora
K. longiflora Schltr.

This is a very confusing species from S. Africa probably Natal region. The photo shown above is that of the type species. The stem is sharply 4-angled. The leaf margins turn reddish on exposure to strong sunlight.
Below are two photos by contributed by Yale Sedman. On the left is the photo of probably the same plant but with redder margins (probably triggered by low night temperatures, to produce more intense coloration).

Also see: K. sexangularis
K. longiflora
Photo: Yale Sedman