The generic Campion name comes from the Greek word lychnos or lamp, describing the bright flowers atop the soft colored leaves and stems. According to "Armitage's Manual of Annulas, Biennials, and Half-Hardy Perennials", they used to be called Champions referring to their use in garlands given to victors in public contests.
There are many Lychnis species and a few Lychnis have been moved into the Silene family so you may see references calling some of them one or the other.
One of the other common ones is Lychnis chalcedonica or Maltese Cross. Wikipedia says it is from Europe, China and Russia. The one we grow so easily is a European variety, Lychnis coronaria or Rose Campion
|Rose campion in February|
They prefer moist soil but tolerate poor soils with some dryness. Missouri Botanical Garden says, "A short-lived perennial that may be best grown as a biennial or annual. Freely self-seeds. Deadheading flowers from plant immediately after bloom will prevent any unwanted self-seeding."
Oh, yes deadheading is what I should do to prevent those large areas of seedlings. Maybe I'll pull the rest of them this afternoon but it's already pretty late since dozens of new plants have come up already this spring.
Here in zone 7 Rose Campion needs afternoon shade. The plants that are still in bloom get a full half day shade. In all the years I've grown them, they have never been bothered by insects chewing them or diseases attacking them.
Interestingly, there isn't much information about the hybrids but they are probably worth looking for if you prefer to avoid the seeding problem.
Some of the other Lychnis -
Lumina series has larger split flowers.
Angel Mix is a seed mix of peach, rose and blue.
Candida is all white.
Peach Blossom has peachy pink flowers.
Rose Angel has a dark eye in a rose flower.
Jozef Babij has beautiful photos of some varieties on his Plant Gallery blog.
Rich Farm Garden sells seeds for a cool pink and white flowering Lychnis.