A little background for you: I grew up in the eastern United States. Raised in Florida, frequently vacationing in or near Shenandoah National Park, and earning my Master’s degree in east Tennessee, I’m used to a certain way things are ‘supposed to’ look. I’ve never been a botanist, but what I associate with ‘normal’ is a kind of deciduous forest. The one time I visited coastal California, I thought I had stepped off the plane in Australia. Everything looked so weird! I didn’t recognize any of the trees.
Flash forward a couple of years, and I find myself working in China for the summer. And let me tell you, China looks ‘normal’ to me. As it so happens, East Asia has a kind of deciduous forest as well.
I’m not the first to notice this similarity. In fact, this strange distribution of seemingly similar plants was one of the first observed cases of disjunct distribution.
The Eastern Asian – Eastern North American Disjunct (EA–ENA disjunct): The observation that many taxa (primarily plants) are found in both Eastern Asia and Eastern North America, but nowhere else.
My interest in this phenomenon goes beyond my observations as a tourist (and academic nomad). Signs of this pattern can be seen in a fossil site I’m interested in, as well as in a recently-discovered living salamander. But that’s for another day!
A Brief History
The forest of Japan, central China, and the southern Appalachians have particularly similar ecologies, and early work focused on botanical expeditions in Japan. Carl Linnaeus’s student, Jonas P. Halenius, was the first to publish this observation in 1750, though the findings were probably written by Linnaeus himself (see Graham, 1966). A number of other botanists commented on the similarity, but it was the work of Asa Gray that drew the attention of scientists, and his letters brought this problem to the attention of Charles Darwin. (Boufford and Spongberg, 1983). The unexpected conclusions of these early studies were that the flora, or plant diversity, of eastern North America (ENA) is more similar to eastern Asia (EA) than to western North America.
Sassafras (Sassafras spp.)
There are three Sassafras species in the world. Two are in Asia (Sassafras randaiense in Taiwan and sassafras tzumu in southeastern China) and one can be found throughout the eastern United States (Sassafras albidum, range map).
Ginseng (Panax spp.)
American ginseng (Panax quinquefolius) is one of 11 species of Ginseng, a group that can be found in colder climates of northeast China, Korea, Bhutan, and eastern Siberia as well as many parts of eastern North America.
Trumpet Creeper (Campsis spp.)
Our familiar Trumpet Creeper (Campsis radicans), which is native to eastern North America but has been naturalized in western states, is one of two species in the genus Campis. The other species (Campsis grandiflora) is native to China and Japan.
More Fun Facts
- 67% of seed-plant genera found in Maine also occur on Japan’s Honshu Island (Qian, 2002).
- The same disjucnt pattern has been found among fungi, arachnids, millipedes, insects, and freshwater fish (Wen, 1999).
Why do these plants show a disjunct pattern in distribution? Do we see this in vertebrate animals? To find out, stay tuned for Parts 2 and 3!