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By studying these various types of fossils, scientists have pieced together the following record of the appearance of terrestrial plants:

Era	Period	Million Years Ago (mya)	Plant Life on Land
Precambrian		3800? to 543
Paleozoic		543 to 248	The first land plants appeared, including mosses, horsetails (~400 mya) and ferns (~350 mya).
Mesozoic	Triassic	248 to 206
	Jurassic	206 to 144	First seed-bearing plants emerged, including conifers such as bald cypress, ginkgos, and cycads (~200 mya)
	Cretaceous	144 to 65	True flowering plants appeared, including magnolias and palms (~140 mya)
Cenozoic		65 to present

(Dates provided by the Geologic Time Scale from the Geological Society of America)

Evolution of Plants
Plant reproductive structures have changed significantly over time and are a good indicator of evolutionary progress. The first land plants, including horsetails and ferns, produced new plants via spores. (See Lesson 1 for an exploration of fern reproduction.) Gymnosperms were the next major group of plants to evolve. They produced true seeds in cone-like structures. After that came the angiosperms – plants with “true flowers” that produce seeds within protected ovaries (fruits). This innovation gave angiosperms an adaptive advantage over naked-seeded gymnosperms, and now they're the most abundant type of plant on the earth. Lesson 2 compares these latter two plant classes.

Dino Plants for Your Garden
Here are descriptions of some plants with prehistoric origins you can use to recreate a Mesozoic environment in your youth garden…shhh…did you see a triceratops over there behind the ferns?

Spore-Bearing Vascular Plants do not have seeds, but instead reproduce through spores in alternating generations. They can also propagate asexually from their underground stems.

Ferns were once the primary vegetation covering the earth! The ancient species were probably similar to the tree ferns, now found only in some tropical regions. These dominant plants of the dinosaur era decomposed to become a major component of coal deposits, an important energy source for us today.

The ability of ferns to adapt and evolve has resulted in more than 12,000 known living species growing in climates from the tundra to the tropics. Some of the earliest species include the maidenhair ferns (Adiantum species), lady ferns (Athyrium species), and autumn fern (Dryopteris erythrosora). The leaves of ferns are borne on feathery fronds arising from rhizomes (underground stem structures that grow just below the soil surface). Ferns range in size and shape from low mounding ground covers to the tree ferns mentioned above. Most ferns grow in woodlands and are well adapted to shady beds and indoor plantings.

The life cycle of ferns varies from the cycle of other common garden plants. Ferns reproduce from spores produced over two distinct generations. The part of the cycle we can easily observe is the development of the green fronds. On the undersides of delicate fern fronds, microscopic, dust-like spores are encased in structures called sporangia. Clusters of sporangia called sori are the scale-like bumps one can see on the underside of the fronds. When the sori turn brown (in natural settings, this is typically after midsummer), they are ripe and ready to release spores. Use a hand lens to look closely at sori – those that are ragged looking have probably already opened and released their spores.

The spores fall to the ground and sprout when temperature and moisture conditions are right. But instead of producing fronds, spores develop into small, green heart-shaped plants known as prothallia. This is the gametophyte generation because male and female reproductive organs produce gametes, akin to pollen and ovaries in seed-bearing plants, that combine with the help of moisture to form spores. It's easy to miss this part cycle because prothallia are tiny and lie close to the ground. When spores are released, they grow into the familiar frond-bearing plant (the sporophyte generation).

For images of the fern lifecycle, visit the Lewis and Clark College Web site or the Fern Site of the University of the West Indies.

Horsetails (Equisetum species) are among the oldest plants in existence. Like their close relatives, the ferns, horsetails reproduce via spores rather than seeds, and horsetail species are also adapted to grow around the globe. They grow in marshy areas and sport two different types of vertical, hollow stems. The first stems appear in the spring and look something like asparagus topped with brown cone-like structures that bear the spores. Later in the year larger stems with stringy, tough leaves emerge, and these give plants a feathery appearance (like a horse’s tail). If planted in a favorable location, horsetails spread quickly — in fact, they are considered invasive weeds in some areas. Check with local native plant organizations or your state's conservation agency about the invasive status of horsetails in your region before planting them in your school landscape.

Another common name for horsetails is scouring rush. This gives away one if its important uses. Horsetails have very fibrous stems that contain silica crystals, making the stems an excellent material for cleaning pots and pans. Historically, people tied bunches of horsetail stems together to form homemade scouring pads for cleaning dishes. Furniture makers also used them to polish their wares. Even though steel wool and sandpaper have replaced them in most places, there are some cultures that still use horsetails for cleaning and polishing.

Gymnosperms produce true seeds in cone-like structures. The word “gymnosperm” means “naked seed,” pointing out the fact that the seeds aren't covered with an ovary (fruit).

Bald Cypress (Taxodium distichum; USDA Zones 5-10) is a tree that can grow in both saturated and dry soils, making it a popular street tree. Bald cypress can reach 120 feet tall, and in wet areas develops distinctive “knees” (hump-shaped roots that grow out of the ground). Although many gymnosperms are evergreen, the bald cypress is deciduous and provides attractive fall color.

Bald cypress seeds are a food source for wildlife including turkeys, wood ducks, and squirrels. Some have referred to the lumber as "wood eternal,” not because the species has been in existence for ages, but because the heartwood is resistant to decay and thus is used to make docks, boats, and bridges. Historically, the Choctaw used the bark for string and rope, and the Seminoles found bald cypress useful for making houses, canoes, and ceremonial objects.

Dawn Redwood (Metasequoia glyptostroboides; USDA Zones 4-8) is another deciduous tree first identified from fossils. Scientists thought it was extinct, but during World War II a grove of surviving trees was discovered in a remote location in China. Seeds were harvested and you can now find this attractive tree in landscapes throughout the world. Dawn redwood can reach heights of more than 120 feet, and it is useful for stabilizing soil in wet areas.

Gingko (Ginkgo biloba; USDA Zones 4-9) is another deciduous landscape tree with unique fan-shaped leaves known for beautiful fall color. Until it was “discovered” growing Japan by a 17th-century Dutch botanist, Europeans believed all ginkgo species were extinct. Male and female reproductive structures form on separate trees, and because the fleshy outer layer of seeds borne on female trees gives off a putrid odor, male trees are a better choice for landscapes. Despite the smell, the seeds are a delicacy in many Asian cultures. Extract from the leaves has become a popular herbal remedy purported to improve memory.

The strobiles on this coontie resemble the plated hide of a dinosaur.

Cycads are gymnosperms that resemble palms. The cycad commonly called coontie (Zamia pumila), with its soft fern-like leaves, is a good candidate for a youth dinosaur garden. This mounding shrub reaches approximately three feet tall and sports evergreen foliage that grows well in either full sun or shade. It’s hardy only to Zone 8, but gardeners in cooler climates can grow it in a container and bring it inside during the winter. Although coontie seeds are poisonous, the Seminoles and early European settlers used the root as an ingredient to make bread.

Sago (Cycas revoluta) is another ancient cycad popular for landscape use, but its sharp-edged leaves make it a less appealing choice than coontie for a youth garden.

Dinosaur Dimensions
Lizards weren’t the only things that grew to huge sizes during the Mesozoic Era – some ancient horsetails were 30 feet tall! Even today, the cones of some cycads, which emerged during the Jurassic Period, can reach three feet in length and 95 pounds!

Angiosperms are plants that produce seeds enclosed in an ovary (fruit). This is a major feature that sets them apart from gymnosperms. (Botanically speaking, most of the "fruits" in the world do not resemble the fruits in the produce section of the grocery store -- in fact, the pips in an orange are the fruit, and the fleshy pulp is the ovary.)

Magnolias (Magnolia species; USDA Zones 4-10) are some of the earliest angiosperms. There are more than 80 different species ranging in size from small shrubs to huge trees. Some, like the southern magnolia, are evergreen, and others, like the saucer magnolia, are deciduous. All are known for their beautiful and often fragrant flowers. Look for varieties that grow well in your area.

Palms are native to tropical and subtropical areas of the globe. Even today the fruits of many palm trees are used for food (think dates and coconuts). Two of the hardiest palms to consider for your dinosaur garden are the pindo palm and the windmill palm. The pindo palm (Butia capitata; USDA Zone 8-9) has a very graceful appearance with feathery leaves that curve down towards the trunk. It also produces a healthy crop of edible orange fruit that some people use to make jelly. The windmill palm (Trachycarpus fortunei) is among the most cold-tolerant palms (hardy in USDA Zones 7b-10, and known to survive winter snow) and is a common landscape plant.

Complementary Garden Features

Here are a few additional ideas for engaging students in hands-on learning about the dinosaur age.