Taxodium Family

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Economic Plant Photographs #40

The Taxodium Family: Taxodiaceae

Beautiful Trees Of Shady Forests

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The traditional taxodium family (Taxodiaceae) contains ten genera and 16 species of cone-bearing trees native to North America, Asia and Tasmania. Because of their scale-like leaves, seed cones and other characteristics, some botanists have consolidated the Taxodiaceae with the cypress family (Cupressaceae). In fact, the seed cones of bald cypress (Taxodium) certainly resemble those of the true cypress (Cupressus). Leaves of the Cupressaceae are opposite in four ranks or whorled, while those of the Taxodiaceae are mostly alternate; however, vegetative characteristics are not reliable for differentiation between families. Modern taxonomists use DNA sequencing and computers to generate phylogenetic "trees" called cladograms. The protein-coding RBCL chloroplast gene is often used at the family level to show relationships between genera and species within a family. The results of these studies indicate that a number of genera formerly assigned to the Taxodiaceae now belong in the Cupressaceae. The principle exception is the genus Sciadopitys (Japanase umbella pine), which was found to be completely unlike the Cupressaceae, and is now placed in the monotypic family Sciadopityaceae. Much to the chagrin of some botanists, sweeping changes are being proposed in the field of conifer taxonomy in order to provide a consistent method of plant classification at the family level. Some drastic changes in the classification of traditional flowering plant families have also been proposed, including the placement of all duckweeds in the arum family (Araceae). If accepted by the botanical community, the incorporation of these changes into botany textbooks, floras, checklists and herbarium collections will be a formidable task.

Sequencing Chloroplast DNA Using PCR Tecnique

Many economically important species belong to the taxodium family, including cultivated ornamentals and timber trees. They are dominant trees in several ecosystems, including temperate forests and swamps. Most of the species are evergreen, but some are deciduous and drop their leaves during the fall months. In addition, the most massive and tallest trees in the world belong to this remarkable plant family. Abundant fossil evidence of these magnificent trees dating back more than 100 million years has been found in north America. Some of today's species look remarkable similar to fossilized trees that lived when dinosaurs walked on the earth.

Sequoiadendron, Sequoia and Metasequoia

A. Giant sequoia (Sequoiadendron giganteum), the world's most massive tree. B. Coast redwood (Sequoia sempervirens), the world's tallest tree, rivaled only by the Australian Eucalyptus regnans. C. Dawn redwood (Metasequoia glyptostroboides), a forest tree of China that once flourished in North America. In Montana, petrified cones from the Eocene Epoch (40-50 million years ago) are remarkably similar to our present-day dawn redwood (red arrow).

Prior to the discovery of ancient bristlecone pines and creosote bush rings, the world's record for longevity went to the magnificent giant sequoia (Sequoiadendron giganteum) of the western slopes of the Sierra Nevada. The greatest authenticated age of a giant sequoia, derived from counting annual rings on a cut stump, was nearly 3,200 years. Several specimen trees of Fitzroya cupressoides, a related conifer in southern Chile and Argentina, are more than 3,500 years old. Although it may fall short of the world's oldest, the giant sequoia has the undisputed record for the world's most massive living thing. The largest tree, named General Sherman, is 275 feet tall with a massive trunk 35 feet in diameter and 102 feet in circumference at the base. Even more remarkable is the fact that at a point 120 feet in the air the trunk of General Sherman is still 17 feet in diameter. It has been estimated to contain over 600,000 board feet of timber, enough to build 120 average-sized houses. In fact, a single giant sequoia may contain more wood than is found on several acres of some of the finest virgin timberland in the Pacific Northwest. The trunk of General Sherman alone weighs nearly 1400 tons. By way of comparison, this is roughly equivalent to 15 adult blue whales, 8 diesel-electric train locomotives, or 20 M-60 battle tanks. It is quite remarkable when you realize that this enormous tree started out about 2,000 years ago as a tiny embryo with a seed only 1/4 of an inch (6 mm) long.

Giant sequoias (Sequoiadendron giganteum) in King's Canyon National Park. The approximate height of a six foot human is shown in red.

Another conifer species called the Montezuma bald cypress (Taxodium mucronatum) occasionally grows into a huge tree. One enormous specimen of this tree grows in the churchyard of Santa Maria de Tule near Oaxaca, Mexico. Called "El Gigante" by the locals, it is one of the most massive of all living things, with a trunk circumference of nearly 118 feet (36 m), larger than the General Sherman giant sequoia. If the perimeter measurement includes the bays and prominences of the buttressed trunk, the circumference exceeds 150 feet (46 m). With a diameter greater than 40 feet (12 m), the trunk of this spectacular tree is literally the size of a house. This gigantic tree was once thought to be 10,000 years old, but botanists now consider it to be a youngster of only 1,500 to 2,000 years. Scientists once thought "El Gigante" was multiple trunks fused together, but recent DNA evidence indicates that this is indeed a single individual.

The world's record for the tallest tree goes to another cone-bearing tree native to California, the coast redwood (Sequoia sempervirens). In fact, this is the state tree of California. The tallest living redwood on record stands 379 feet (116 m), 64 feet (20 m) taller than the Statue of Liberty (from the base to the torch). Redwoods are native to a narrow strip of land (fog belt) from southern Monterey County to the southwestern corner of Oregon. Only about 15 percent of the redwood forests are protected within state and national parks. California redwoods are rivaled in size by the amazing flowering Australian tree (Eucalyptus regnans). The record for the tallest tree of all time has been debated by botanists for centuries. Some amazing claims for towering Douglas fir (Pseudotsuga menziesii) and E. regnans exceeding 400 feet (122 m) have never been substantiated by a qualified surveyor. In 1872, a fallen E. regnans 18 feet (5.5 m) in diameter and 435 feet (132 m) tall was reported by William Ferguson, making it the tallest (or perhaps longest) dead tree. According to the monograph on Eucalyptus by Stan Kelly (Volume 1 of Eucalypts, 1977), trees of E. regnans well over 300 feet (91 m) tall have been measured, but the tallest tree known to be standing at present is 322 feet (98 m). The redwood shown in the left image is over 250 feet tall (76 m), roughly twice the height of the tallest tree in San Diego County.

Giant coast redwoods (Sequoia sempervirens) at Henry Cowell Redwoods State Park and Big Basin Redwoods State Park in Santa Cruz County, California. The largest trees are over 300 feet (91 m) tall and 17 feet (5.2 m) in diameter. They sprouted from seeds the size of oatmeal flakes nearly 2000 years ago, and grew into giants as tall as the Statue of Liberty (from the foundation of pedestal to torch).

California redwoods are named for the color of their bark and heartwood. The high tannin content imparts the reddish coloration and gives the wood a remarkable resistance to fungal rot and insect infestations. The thick, fibrous bark has an even higher tannin content, and insulates the inner cambium layer from occasional natural fires. Giant sequoias of the Sierra Nevada have similar red heartwood and fire-resistant bark. Fire-scarred trunks on old patriarch trees are evidence that they survived many fires during the past 20 or 30 centuries.

A redwood block showing the light sapwood and reddish heartwood.

Redwoods and giant sequoias were once classified in the same genus Sequoia. In 1939 botanist J.T. Buchholz placed the giant sequoia in its present genus of Sequoiadendron. There are a number of substantial taxonomic differences between the two species, including their chromosome numbers. The giant sequoia has a diploid number of 22 with two sets of chromosomes, while redwoods have a hexaploid number of 66 with six sets of chromosomes. In addition, redwoods commonly sprout from adventitious buds in their root crowns. Cut stumps can resprout at any season of the year within one month. Botanists have theorized that redwoods originated from hybridization between a Metasequoia and another extinct conifer during the late Mesozoic era (70-120 million years ago).

Petrified California Redwoods:

Approximately three million years ago, redwoods (Sequoia sempervirens) in the coast ranges of northern California (west of present-day Calistoga) were leveled by a powerful volcanic eruption from the direction of Mt. St. Helena seven miles (11.3 km) to the northeast. The blast knocked the trees down and covered them with volcanic ash. Over the centuries, woody tissue in the trees was permeated by water-laden silicates. The hollow xylem cells were gradually replaced with crystalized silica until the entire trees were converted into stone. The petrified wood also contains veins of quartz or druzy quartz which gives the wood a sparkly appearance. Unlike petrified trees of other regions, the trees are light-colored due to the sandy, creamy-white ash. At the time of their deaths, the largest trees were nearly 2,000 years old. [During the Mt. St. Helens eruption in southern Washington in 1980, most of the conifers were knocked down but not buried, so they will not be petrified.]

The "Petrified Forest" west of Calistoga was discovered in 1870 by Charles Evans, known as "Petrified Charlie." It is privately owned and is a California Registered Historical Landmark. This is certainly one of California's little-known natural wonders, and a very rewarding field trip.

This fallen redwood tree has remained in the same position for the past 30,000 centuries. Its orientation corresponds to the force of a volcanic explosion from the direction of Mt. St. Helena that blew it over. During this time interval is has completey turned into stone, with all of its cellular detail perfectly preserved in silica. The trunk is six feet (1.8 m) in diameter and 60 feet 18.3 m) in length.

This petrified redwood has a trunk diameter of over eight feet (2.4 m). Like other petrified trees of the fallen forest, the bark and wood tissue are perfectly preserved. Called the Robert Louis Stevenson Tree, this redwood patriarch commemorates the discovery of Petrified Forest by Charles Evans in 1870, and his meeting with the famous author in 1880, immortalized in the book The Silverado Squatters.

Left: A coast live oak (Quercus agrifolia) growing up through a break in the massive petrified trunk of a California redwood (Sequoia sempervirens). Right: A piece of perfectly preserved petrified redwood. These fossil redwoods formed a thriving forest in this region about 30,000 centuries ago.

The Dawn Redwood:

Another ancient cone-bearing tree that was thought to be extinct but was later discovered growing in a remote valley of Central China is the dawn redwood (Metasequoia glyptostroboides). The genus Metasequoia was first described from fossil material by the Japanese paleobotanist Shigeru Miki in 1941. In 1948, paleobotanist Dr. Ralph Chaney of the University of California, Berkeley led a 10,000 mile expedition up the Yangtze River and across three mountain ranges to a lush, fog-shrouded valley where a thousand dawn redwoods were growing. Leaf imprints and petrified wood of ancestral dawn redwoods resembling the present-day species have been found in Cretaceous deposits throughout North America. Some of the fossils date back nearly 90 million years, from a time when the climate was much more humid than today. It has been estimated that the relict forest in China may have been surviving in this remote primeval valley for countless thousands of years. The seed cones and foliage of the dawn redwood superficially resemble our California coast redwood (Sequoia sempervirens), except that the dawn redwood is deciduous and loses its leaves during the winter months. All North American plantings of this superb cone-bearing tree came from the seeds (and their progeny) originally collected in China. Indeed this "living fossil" was brought back to its ancestral home.

The foliage and cones of the dawn redwood (Metasequoia glyptostroboides) superficially resemble the California coast redwood (Sequoia sempervirens). This lovely deciduous conifer once coexisted with dinosaurs in North America during the Cretaceous Period 90 million years ago. The cones date back to the Eocene Epoch of the Tertiary Period (about 40-50 million years ago), a time when many modern mammalian orders appeared in the fossil record. Close examination of the fossil cones reveals that they are remarkably similar to our present-day dawn redwood.

Fossil Redwoods In North America

A 25 million-year-old leaf of dawn redwood (Metasequoia) from the scenic John Day Fossil Beds National Monument in Eastern Oregon. Close examination of the needles reveals that this extinct species is not a Sequoia, but is remarkably similar to our present-day Metasequoia. The soft brown shale is from ancient Miocene lake bed sediments made from layers of volcanic ash and silt. Many conifers and broad-leaf angiosperms have been identified from this fossil-rich shale (note other leaves in photo).

Left: Present-day seed cones of the dawn redwood (Metasequoia glyptostroboides) growing at the San Diego Wild Animal Park. Right: Petrified Metasequoia seed cones from the Fort Union Formation of southeastern Montana. The cones date back to the Eocene Epoch of the Tertiary Period (about 40-50 million years ago), a time when many modern mammalian orders appeared in the fossil record. Close examination of the fossil cones reveals that they are remarkably similar to our present-day dawn redwood. Fossil evidence from cones, leaves and petrified trunks indicates that Metasequoia forests once dominated vast areas of western North America after the demise of the dinosaurs.

Lamar River Valley and Specimen Ridge, Yellowstone National Park. This beautiful mountain range contains well-preserved petrified redwood trees that are still in their original upright position. The trees in the foreground are narrow-leaf cottonwood (Populus angustifolia). In the distant foothills are quaking aspen (P. tremuloides).

Left: A petrified redwood tree in Yellowstone National Park. The trunk has remained in its upright position since the Eocene Epoch, 50 million years ago. Right: A 50 million-year-old piece of petrified wood (possibly redwood) from nearby Lamar Valley compared with a piece of recent dead wood. Both are radial sections with parallel annual rings. Can you tell which of the two pieces is petrified?

The ancient trees in most North American petrified forests are in horizontal positions. They were carried by streams and deposited in alluvial flood plains. Petrified trees on Specimen Ridge are unusual because they are still in their upright positions. Volcanic eruptions in this region during the Eocene epoch (50 million years ago) triggered massive landslides into mountain and valley streams. The mixture of ash, water and sand buried entire forests in their original standing positions, including redwood trees very similar to those of coastal California. Before the wood decayed, silca from the volcanic mud flow replaced the cell contents (lumens), literally creating forests of stone. Unlike other petrified woods that are completely replaced with minerals, the petrified trees of this region have lignified cell walls of the original xylem tissue that are still intact.

Magnified cross section of petrified redwood from Oregon showing detail of xylem tissue (tracheids). There are five light-colored bands of larger cells representing five spring growth seasons. Four narrow, dark bands of smaller cells represent four summer seasons. Although it is as perfectly preserved as freshly cut redwood, this petrified sample is at least 15 million years old. In fact these hollow, tubular cells carried water molecules up a tree trunk about 150,000 ceturies ago.

The Bald Cypresses (Taxodium)

Three North American species of Taxodium, the type genus for Taxodiaceae: A. Pond cypress (T. ascendens), also known as T. distichum var. nutans. This species has many slender branchlets with appressed awl-shaped leaves that branch (ascend) from larger branchlets (red arrow). It apparently does not cross pollinate with the closely related T. distichum. B. Bald or Swamp Cypress (T. distichum). This species is native to swamplands of the southeastern United States along with T. ascendens. C. Montezuma bald cypress (T. mucronatum), a Mexican species native from Sonora and Coahuila south to Guatemala. It is planted in the United States and grows well in areas that are not inundated by water.

The Spanish moss that hangs from the branches of bald cypress trees (Taxodium distichum) in swamps of the southeastern United States is not a lichen or a moss. It is a flowering plant in the pineapple or bromeliad family (Bromeliaceae) named Tillandisia usneoides. The specific epithet usneoides means "usnea-like" referring to an epiphytic lichen namedUsnea (sometimes called "old mans's beard"). The right photo shows the small greenish flower of Tillandsia, proof that this epiphyte is indeed a flowering plant and not a lichen or moss.

A swamp of bald cypress (Taxodium distichum) in the Florida Everglades. The erect, woody extensions from the roots are called "cypress knees" or pneumatophores. Some botanists maintain that pores in the "knees" fascilitate gas exchange between the water-logged roots and the atmosphere, although other botanists disagree with this theory. When photographing cypress knees it is wise to be aware of nearby alligators basking along the water's edge.

Near Kupanda Falls at the San Diego Wild Animal Park, cypress knees (pneumatophores) from the bald cypress (Taxodium distichum) have developed along the rushing water near a foot bridge.

Cryptomeria and Cunninghamia

Left: Japanese cedar (Cryptomeria japonica), a tall Asian conifer with foliage similar to the California giant sequoia (Sequoiadendron giganteum). The Chinese C. fortunei grows to a height of 240 feet (73 m) and is one of the tallest trees in China. Right: Chinese fir (Cunninghamia lanceolata), a tall timber tree in China. Like the coast redwood (Sequoia sempervirens), this species commonly stump sprouts from the base of the tree.

Taiwania: A Rare Conifer Of Taiwan

Taiwania (Taiwania cryptomerioides), an interesting coniferous tree closely related to the genus Cryptomeria. It has adult scalelike leaves and juvenile awl-shaped leaves on the same plant. This photo shows the sharp-pointed awl-shaped leaves. In its native habitat of the mountains of Taiwan, this tree may reach 175 feet (53 m) in height.

Japanese Umbrella Pine (Sciadopitys)

Japanese umbrella pine (Sciadopitys verticillata), showing clusters of long, flattened leaves at the tips of branchlets. Each linear leaf arises in the axil of a minute scalelike leaf. This distinctive cone-bearing tree is native to mountains of central and southwest Japan. Its clusters of long, flattened leaves are unlike other members of the taxodium family. In fact, some references list it in the cypress family (Cupressaceae). Recent DNA studies indicate that this species belongs to its own monotypic family, the Sciadopityaceae.

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