Admittedly, kalmia is a bit tricky to grow and not inclined to flower well in our cooler, relatively sunless summers. But kalmia is enjoying a bit of a comeback. Newer varieties from the US seem to be more likely to flower as young plants and are in general much more floriferous. They are also generally smaller in size and this is probably linked to earlier flowering.
Just like heathers, rhododendrons and pieris, the flowers are open, rounded bells. Not immediately linked to heathers or rhododendrons, but a kind of half-way house between the two – bigger than heathers, but more bell shaped and not as open or as big as most rhododendrons. Carried in big bunches similar to rhododendrons, as is the size of the leaf, which varies depending on the species and variety, but can be as long as 15cm.