Lee Valley & Veritas

Gardening Newsletter
  Volume 9, Issue 2 - February 2014  
 
Living Fossils in the Garden
Monkey puzzle tree
The distinctive leaves of the monkey puzzle tree, a living fossil that dates back to the Triassic period (about 250 to about 200 million years ago).
 
When discussing living fossils, it’s necessary to take a look at the long-distant past. The oldest life forms date back about 3.5 billion years and were found in marine sediments. Land remained uninhabited until the Silurian period (a geological period dating from about 443 to about 416 million years ago), which saw the first clear evidence of terrestrial plant life.

These simple terrestrial plants developed and diversified during the next geological period, the Devonian (about 417 to about 359 million years ago). Initially, the land was “greened” with primitive ferns and horsetails, both members of the large family that reproduced by spores. Today’s horsetails (Equisetum spp.) are truly living fossils as they are the only surviving genus of the entire family. The feathery common horsetail (Equisetum arvense) is a well-known, pesky weed. Though it doesn’t grow taller than about 40cm, some of its long-extinct relatives grew into large trees that are abundant in coal deposits from the next period, the Carboniferous (about 359 to 299 million years ago).
 
Cycad (Dioon sonorense)
This extremely rare cycad (Dioon sonorense) superficially resembles ferns or palms.
 
The plant life of this next period was extensive and lush. It included impressive fern-like trees, giant horsetails and tree-like ancestors of club mosses. Additionally, the first primitive conifers, true ferns and seed ferns appeared. The seed ferns provided the beginning of a new group of plants, the cycads, which appeared at the onset of the next period, the Permian (about 299 to about 250 million years ago). Although these plants once covered much of the planet, their range is now limited to the tropics. Today’s cycads are among the rarest plants on earth and are thereby in danger of extinction. Fortunately, there are many efforts to conserve and protect them. Cycads are commonly mistaken for tree ferns or palms, but they’re actually early conifers. They have distinctive traits from other seed plants, such as motile sperm cells and coralloid roots.
 
Monkey puzzle tree   New growth
The monkey puzzle tree   New growth on the monkey puzzle tree
 
Young female seed-bearing cones   Scaly trunk
The tree's young female seed-bearing cones   The tree’s scaly trunk
 
The Permian period ended with the largest mass extinction in Earth’s history, known as “The Great Dying”, during which more than 90% of species became extinct. The recovery in the following period, the Triassic (about 250 to about 200 million years ago), brought two new conifers, the monkey-puzzle tree (Araucaria araucana) and the Japanese umbrella pine (Sciadopitys verticillata). Although close relatives of the monkey puzzle tree already existed during the Carboniferous period, the tree as we now know it appeared in the early Triassic. This distinctive, pyramidal, coniferous evergreen is often described as beautiful but bizarre. Its trunk is scaly and ridged with a diamond pattern that resembles a pineapple's peel. The tree’s dense, triangular leaves overlap to completely cover each branch, creating a somewhat reptilian appearance. Perhaps this growth habit developed as a deterrent to grazing dinosaurs.

The relatively younger Japanese umbrella pine appeared in the fossil record dating to the mid-Triassic period. It’s an evergreen conifer but not a pine, and is the only living member of its genus. At first glance, a young umbrella pine looks like a little plastic Christmas tree. It grows slowly, forming a dense, pyramidal shape with glossy, dark-green needles. Each season, its stems produce a set of needles that spread out in whorls like the spokes of an umbrella.
 
Japanese umbrella pine   Japanese umbrella pine needles
A Japanese umbrella pine ready to send new shoots in the spring.   The arrangement of the needles resemble the spokes of an umbrella.
 
The flora of the next period, the Jurassic (about 199 to about 146 million years ago) was tropical in nature. Conifers, mostly cycads, were the predominant plants during this period. In the early Jurassic, the ginkgos became abundant, though the earliest fossil record of these primitive conifers dates back to the Permian period. The entire family was thought to be extinct until a German botanist named Engelbert Kaempfer “rediscovered” the ginkgo (Ginkgo biloba) in China in 1691. Cycads are probably its closest living relative, though the tree shows several significant differences. It has deciduous leaves instead of evergreen foliage, and its seeds are enclosed by a fleshy, fruit-like structure instead of by cones.

The discovery of another tree dating to the Jurassic period, the Wollemi pine (Wollemia nobilis), created a botanical sensation. It occurred in 1994 in Australia’s Wollemi National Park, located northwest of Sydney. The tree was discovered by David Noble, a park ranger. The Wollemi is an evergreen conifer but not a pine. Its closest living relative is probably the monkey puzzle tree. Today, this species faces a risk of extinction in the wild; however, there are many efforts to protect these living fossils, including establishing a stock of nursery plants. The Wollemi pine has several very distinctive features, including dark-brown knobby bark and leaves with shoots arranged in four flattened ranks. As the foliage matures, it changes from a bright lime green to an unusual yellow green.
 
Wollemi pine   New growth
An example of the Wollemi pine   New growth on the Wollemi pine
 
The Earth’s landscape changed dramatically during the next period, the Cretaceous (about 146 to about 65.5 million years ago), due to the emergence of flowering plants. They first appeared in the Lower Cretaceous 125 million years ago and developed with astonishing speed due to their fast reproduction rates, rapid growth rates and amazing adaptability. Their success contributed to a decline in less adaptable species, such as ferns and cycads. Conifers, however, remained in large numbers.

During this period, a new conifer appeared called the Dawn redwood (Metasequoia glyptostroboides). Previously, the tree had been known only from fossil records dating back 100 million years. In 1946, a few living species were found in central China. Seeds were collected and distributed to botanical gardens in the United States and Europe, where they were cultivated. Dawn redwood is a conifer but again a distinctive one due to its deciduous habit and its two-ranked, opposite, needle-like soft leaves. Its ornamental, bright-green foliage turns reddish-brown before dropping in autumn.
 
Dawn redwood bark   Dawn redwood new spring foliage
The dawn redwood trunk features cinnamon-colored bark   The tree's delicate spring foliage will eventually turn reddish brown and drop in the fall.
 
Most living fossils have remained nearly unchanged for millions of years and are therefore almost identical to their ancestors. They are long-lived, slow-growing plants, with the exception of the dawn redwood, which can reach an overwhelming size in just a couple of decades. Today, many living fossils grow in cities as ornamental trees. The most successful example is the pollution-tolerant and disease- and pest-resistant ginkgo. It’s somewhat of a paradox that the prehistoric ginkgo can grow in a modern city environment where many other trees can’t survive.

Living fossils are easy to grow in the home garden, but they range in suitability. The relatively small Japanese umbrella pine makes a good potted plant (for a period of time). Other giant specimens, such as the monkey puzzle tree and dawn redwood, are better suited to large gardens or public parks. Many nurseries offer various miniature ginkgos and umbrella pines, as well as dawn redwoods that are not dwarfs but grow to reasonable sizes. Some cycads, such as the diminutive red dwarf cycad (Zamia pygmaea), make good house plants.
 
Semi-dwarf ginkgo 'Spring Grove'
The semi-dwarf ginkgo ‘Spring Grove’ makes a wonderful addition to the home garden.
 
Having a living fossil in your garden provides a fascinating conversation piece and, in some cases, may help with the preservation of a rare or endangered species. On the downside, purchasing a living fossil may be a challenge in terms of cost and where to find one. I believe it can be worth the trouble due to the awe factor inspired by these true “life wonders”, which have survived much longer than us humans, a relatively new species.  

Text and photos by Gina Dobrodzicka

Gina Dobrodzicka is a freelance writer and trained horticulturalist who volunteered with Master Gardeners of Ottawa-Carleton for five years. Currently, she volunteers with the Vancouver Master Gardeners Chapter, the South Surrey Garden Club and Darts Hill Garden Society.Her website is www.gdgardendesign.com.
 
 
 
 
     
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