Garden geography

One of the things that I find interesting about gardening is something that many gardeners probably don't think very much about - where the plants in the garden originally came from. Most garden plants, whether flowers, herbs, or vegetables, have been selectively bred to some degree to produce larger flowers or leaves or roots, but most of them still have a lot in common with their wild ancestors. So, in a sense, even an average suburban garden is a sort of herbarium or botanical garden with specimens that originate in various parts of the world. Here are just a few samples from my particular garden:

Dicentra eximia - Wild bleeding heart; native to
eastern United States, mainly Appalachian mountains

Syringa vulgaris - Common lilac; native to the
Balkan peninsula of southeastern Europe

Podophyllum peltatum - Mayapple; native to
eastern United States

Cercis canadensis - Eastern redbud; native to
eastern United States (but not Canada, in spite of the name)

Centaurea cyanus - Cornflower or Bachelor's button; native to
most parts of Europe

Rosa carolina - Pasture rose or Carolina rose; native
to eastern United States and southeastern Canada

Rudbeckia hirta - Black-eyed susan; native to
central and eastern United States and Canada

Athyrium niponicum - Japanese painted fern; native to
Japan (duh!), northern China, Korea, Taiwan

Leucanthemum x superbum - Shasta daisy; hybrid of two species
native to Europe -- with Apis mellifera - Honey bee; native to parts of Asia,
Africa, and Europe

Dicentra spectabilis - Bleeding heart or Lyre-flower; native to
southeastern Siberia, northern China, Korea, and Japan

Rhododendron maximum - Great rhododendron; native to
eastern United States and southeastern Canada

You may notice that all of these plants are natives of either eastern North America, Europe, or the northern China-Korea-Japan area. This isn't an accident - the northeastern part of the United States has a type of climate sometimes known as humid continental. There are three large areas of land on earth that have this climate:

Image from here on Wikipedia - see this article.

The native ranges of most of the common (and quite a few of the less common) garden plants that grow in the northeastern United States fall mostly within one of these three zones.