Geographic Diversity in the Azalea Garden: Arisaema, Disporum, and Podophyllum
Posted on June 1st, 2011
Arusaema Sikokianum
As you stroll through the Azalea Garden you will see a large number of North American native species and their closely related Asian cousins. Many of these plants share a genus, but have different species names. For example, the garden contains many interesting Asian Arisaema commonly known as Jack-in-the-pulpits.
In botanical nomenclature, plants are identified by a two-part, or binomial, name. A plants genus denotes that it belongs to one group, while the species name marks it as a member of a sub-group of the genus. There are many Arisaema in the world, yet Arisaema triphyllum refers solely to a specific Jack-in-the-pulpit, one of North Americas native Arisaema.
Why are there so many closely related species on two continents separated by a large ocean? Many of these Asian/North American counterparts come from a common genetic pool. It is possible to imagine that over time seeds have been dispersed by glaciers, wind, birds, or other animals. While this certainly has occurred it would be more likely to have happened on a contiguous landmass.
The most compelling theory for why these closely related floras are found on the opposite sides of an ocean comes from the scientific theory of continental drift, the process by which the continents have moved apart over millions of years. About 250 million to 65 million years ago, during the Mesozoic era, the landmass Pangaea began to split apart; the northern part of the supercontinent broke off into Laurasia (North America and Eurasia). As Asia and North America drifted away from each other, the plants that had been one genus began to evolve. Time, combined with changes in climate, and range fragmentation helped these once related plants to diversify and evolve into new species. Why are there so many Asian Arisaema compared with only two Arisaema native to North America? During the last ice age, parts of eastern Asia remained ice-free. This resulted in a greater diversity in the flora there.
How do botanists know that these plants are closely related? Just looking at the plants can be deceptive, so they also collect evidence from the fossil record and analyze the plants genes in order to determine relationships.
In this video Kristen Schleiter, Curator of Outdoor Gardens and Woody Plants, discusses many of the Azalea Gardens geographically diverse perennials.
Heres a closer look at some of the plants in the Azalea Garden.
Arisaema
The two species of Jack-in-the-pulpit native to North America, Arisaema triphyllum and Arisaema dracontium, thrive in moist to wet soil. Asian Arisaema also enjoy moisture, but unlike the North American natives, require good drainage. All Jack-in-the-pulpits are well suited to a woodland understory, flower in spring, generally produce red berries in fall, and are deer resistant. The common names of ArisaemaJack-in-the-pulpit and cobra-lilyrefer to the unique morphology of these plants; some look like a little preacher on his pulpit, while others look like the infamous snake. The plant is composed of a spadix and a spathe. The spathe is the leaf-like hooded bract that can be seen as a pulpit or cobras hood. The spadix is the flower, it is the spike-like thing that pokes out of the spathe, in other words, it is the Jack.
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 cotton swab that emerges from a deep-purple spathe. It is a startling and striking combination, flowering in early spring.
Disporum flavum
Disporum
The Azalea Garden also includes two Asian fairy bells (Disporum).
Podophyllum
Mayapples present another example of plant diversification from Asia to North America.
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Tags: Azalea Garden, Garden
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