Here's a classic shrub, Rhododendron maximum var. 'Roseum' growing in the Liz Christy Garden.
Rhododendron is an amazing genus, with over 900 species and countless hybrids. One reason there are so many cultivars is because this plant can cross pollinate within the genus. You see, most plants can only create seeds, or offspring, with another individual of its species. But, Rhododendron maximum, for example, could 'mate' very easily with Rhododendron catawbiense to make a new hybrid.
Despite the fact that this plant is so damn fertile, it can be really tough to grow. It's part of the lovely Ericaceae family, which includes Kalmia latifolia (mountain laurel), Oxydendron arboreum (sourwood), as well as Erica and Vaccinium species (heathers and blueberries, respectively). If you know plants, you may note a trend: all of those plants prefer or even, insist upon, great drainage and acidic soil. ...Ericaceous plants are beautiful, but like so many beautiful things, they are high, high maintenance.
-dendron, as you may guess, means 'tree.' Rhodo- means 'rose.' The genus name is thus essentially 'rosetree' referring to the large lustrous flowers. Though it always strikes me as odd since the flowers look so much more like a trumpet lily than a rose.