There are few things on a hike that get me pumped more than hearing someone call out "Hey, I found something weird over here!" It's even more exciting when that person knows what they are talking about. Sometimes that "something" is a familiar species in a strange spot, or growing in a strange way. Sometimes, however, it is something new and exciting that you have been wanting to encounter for years.
This is how I finally met the American climbing fern (Lygodium palmatum). Tangled among the branches of a shrub was indeed a strange site. The tiny, palmate pinnules are not a dead giveaway as to its true identity. Regardless of looks, this is in fact a fern. It is the only member of this genus native to North America. Its cousins, the Japanese climbing fern (Lygodium japonicum) and the Old World climbing fern (Lygodium microphyllum) can also be found on this continent but they have become very invasive in the southeast.
I know what some of you may be thinking, "if this is a fern then where are the fronds?" This was my first thought as well. My first guess was aimed at each palmate leaf. Wrong. The correct answer is the whole vine! Each climbing vine of this fern is a single frond. The palmate leaves are actually the pinnules. The stem, or rachis as it is called in ferns, twines around branches and stems in a vine-like fashion, unfurling pinnules as it goes. What is most impressive is that these fronds can grow as long as 15 feet. Quite impressive by North American fern standards. Fertile pinnules form at the ends of these fronds. Their lacy appearance is quite beautiful juxtaposed with the hand-like, sterile pinnules.
The American climbing fern can be found growing throughout eastern North America. It is a fern of wet places, enjoying acidic soils and bright sunlight. Unfortunately its preference for wetlands has landed it on threatened and endangered lists throughout its range. Our nasty habit of draining, farming, and developing wetlands means that the American climbing fern (as well as many of the other species it shares its habitat with) is losing habitat at an alarming rate.
Further Reading:
http://plants.usda.gov/core/profile?symbol=LYPA3