Noteworthy Books Related to this Subject
Native and Asian Counterparts
As you stroll through the Azalea Garden you will see a large number of Asian species that resemble North American natives. Notice on the plant labels that the genus (the generic name) of these is often the same while the species (the specific name) is different.
In botanical nomenclature, plants are identified by a two-part (binomial) name. The genus is analogous to a person's last name, denoting a group that contains one or many individuals. The species name is equivalent to a person's first name. There are many Smiths, but Jeremiah Smith refers to an individual; likewise there are many Jack-in-the-pulpits (Arisaema), yet Arisaema triphyllum refers to a specific Jack-in-the-pulpit, one of our native Arisaema.
Why do we have so many closely related species on the continents of North America and Asia? If the species were unrelated, it would be a case of convergent evolution, in which distinct lineages evolve similar traits. Many of these Asian/North American counterparts, however, come from a common genetic pool, so there must be another explanation.
One could conjecture that over time seeds were dispersed by glaciers, wind, birds or other animals. While this certainly happened, the hitch with such a hypothesis is that the seeds, then, would most likely appear on contiguous landmasses. Yet, many of the members of the same genera are found only in Asia and North America.
The most compelling theory why closely related floras are found on both of these continents is the theory of continental drifts. Millions of years ago all the continents were interconnected in one huge landmass called Pangaea (Greek for "all lands"). During the Mesozoic era (from about 250 million to 65 million years ago), the landmass began to split apart according to the theory of plate tectonics; the northern part of the hemisphere broke off into Laurasia (North America and Eurasia). Combined with prehistoric climatic changes such as global cooling that drove many species in Eurasia south, range fragmentation occurred where plant populations were separated geographically. Similarities in native North American and Asian species are seen through their shared ancestry while the glorious diversity and differences result when wild populations are isolated and are influenced by regional environmental factors (divergent evolution).
How do botanists know if plants are closely related? A look alone at the form (morphology) of a plant can be deceptive, so they collect evidence from fossil records (paleobotany) and uncover and analyze genetic relationships in molecular systematics.
Let us take a look at a few examples.
The NYBG Azalea Garden contains many interesting Asian Arisaema. While our two native species of Jack-in-the-pulpits (Arisaema triphyllum and Arisaema dracontium) thrive in moist to wet soil, the Asian counterparts, which also enjoy moisture, require good drainage. All Jack-in-the pulpits are well suited to a woodland understory, flower in spring and generally produce red berries in fall. They are also referred to as cobra-lilies, depending on the shape of the hood, and are deer resistant.
A quick lesson on the anatomy of the Jack-in-the pulpit/cobra-lily: the flower is composed of a spadix and a spathe. The spadix is the flower, the spike-like inflorescence that pokes out of the spathe; in other words, it is the Jack. The spathe is the leaf-like, hooded bract, the pulpit.
Arisaema consanguineum 'The Perfect Wave' is an adaptable cobra lily that can grow in sun or shade, moist or dry. The cultivar reaches close to a 3 feet tall with blue-gray foliage; the coloring is more pronounced in the shade. The hood (spathe) ends in a long, dangling thread.
Arisaema fargesii is easy to grow with its giant, trifoliate leaves opening in early spring and the flower appearing in June. The dramatic wine-colored and white-striped spathe looks like a cobra head with a reddish spadix poking out like a narrow tongue.
Arisaema sikokianum is probably the most sought after species on the market. It has handsome foliage: each leaf has three or five leaflets that are often mottled with silver. The spadix looks like a jumbo, white Q-tip that emerges from a deep-purple spathe. It is startling and striking combination, flowering in early spring.
Arisaema thunbergii subsp. urashima grows 15 inches tall and its foliage looks like a horseshoe with 11 to 15 narrow leaflets radiating outward. The spadix on this Arisaema looks like a whip that extends well past the spathe. The spathe is maroon with a speckled, white base.
These are just a few of many Arisaema from Japan, China and Taiwan that are in NYBG's collection. Why are there so many Asian Arisaema compared with only two native Arisaema? During the last ice age, parts of Eastern Asia were not covered by a glacier. As a result there is a greater diversity in the flora there, both greater diversity of species and in the variation found in the species.
The Azalea Garden also includes two Asian fairy bells (Disporum).
Disporum longistylum 'Night Heron' is a cultivar that emerges with chocolate-brown foliage in spring then fades to chocolate-green in summer. It can reach 4 to 6 feet tall and looks more like a dancing bamboo than a fairy bell. Later in the season, fairy bells are covered with black berries.
Disporum flavum, is a yellow fairy bell from Korea that looks similar to Solomon's seal (Polygonatum), growing 30 inches tall and producing creamy-yellow, nodding, bell-like flowers.
Another example of Asian diversity in the Azalea Garden, and a native counterpart, is the Himalayan mayapple (Podophyllum hexandrum 'Majus'), which has the typical, broad, umbrella-shaped foliage of our native mayapple (Podophyllum peltatum) with the added bonus of black-and-purple marbling and lovely pink-white, upward-facing, cup-shaped flowers in May. Another Asian mayapple (Podophyllum pleianthum) is a taller, glossier, larger-leaved version of our native, reaching 2 feet tall with 13-inch-wide foliage. Mayapples are deer resistant.