354 CHAPTER 12 Classifying Plants

Seedless Nonvascular PlantsIf you were asked to name the parts of a plant, you probably

would list roots, stems, leaves, and flowers. You also mightknow that many plants grow from seeds. However, some plants,called nonvascular plants, do not have all of these parts and don’tgrow from seeds. Figure 7 shows some types of common non-vascular plants.

Nonvascular plants usually are just a few cells thick and only 2 cm to 5 cm in height. Most have stalks that look like stems andgreen, leaflike growths. Instead of roots, threadlike structurescalled rhizoids (RI zoydz) anchor them where they grow. Mostnonvascular plants grow in places that are damp. Water isabsorbed and distributed directly through their cell membranesand cell walls. Nonvascular plants also do not have flowers orcones that produce seeds. They reproduce by spores. Mosses, liv-erworts, and hornworts are examples of nonvascular plants.

Mosses The largest group of nonvascular plants are themosses, like the ones in Figure 7. They have green, leaflikegrowths arranged around a central stalk. Their rhizoids aremade of many cells. Sometimes stalks with caps grow from mossplants. Reproductive cells called spores are produced in the capson these stalks. Mosses often grow on tree trunks and rocks orthe ground. Although they commonly are found in damp areas,some are adapted to living in deserts.

■ Distinguish between characteris-tics of seedless nonvascularplants and seedless vascularplants.

■ Identify the importance of somenonvascular and vascular plants.

Seedless plants are among the first to grow in damaged or disturbedenvironments and help build soil forthe growth of other plants.

Seedless Plants

Close-up of moss plants

Figure 7 The seedless nonvas-cular plants include mosses, liver-worts, and hornworts.

Close-up of a hornwortClose-up of a liverwort

Benchmarks—SC.F.1.3.1 Annually Assessed (pp. 354–356): The student understands that living thingsare composed of major systems that function in reproduction, growth, maintenance, and regulation;SC.F.2.3.4 (p. 357): knows that the fossil record provides evidence that changes in the kinds of plantsand animals in the environment have been occurring over time.

Also covers: SC.D.1.3.4 Annually Assessed (p. 355), SC.H.1.3.5 Annually Assessed (p. 355)

Review Vocabularyspore: waterproof reproductivecell

New Vocabulary• rhizoid

• pioneer species

(l)Larry West/Bruce Coleman, Inc., (c)Scott Camazine/Photo Researchers, (r)Kathy Merrifield/Photo Researchers

SECTION 2 Seedless Plants 355

Liverworts In the ninth century, liverworts were thought tobe useful in treating diseases of the liver. The suffix -wort means“herb,” so the word liverwort means “herb for the liver.”Liverworts are rootless plants with flattened, leaflike bodies, asshown in Figure 7. They usually have one-celled rhizoids.

Hornworts Most hornworts are less than 2.5 cm in diameterand have a flattened body like liverworts, as shown in Figure 7.Unlike other nonvascular plants, almost all hornworts have onlyone chloroplast in each of their cells. Hornworts get their namefrom their spore-producing structures, which look like tinyhorns of cattle.

Nonvascular Plants and theEnvironment Mosses and liverworts

are important in the ecology of many areas. Although theyrequire moist conditions to grow and reproduce, many ofthem can withstand long, dry periods. They can grow in thin soil and in soils where other plants could not grow, as shown in Figure 8.

Spores of mosses and liverworts are carried by the wind.They can grow into plants if they settle where growing condi-tions are right. Mosses often are among the first plants to growin new or disturbed environments, such as lava fields or after aforest fire. Organisms that are the first to grow in new or dis-turbed areas are called pioneer species. As pioneer plants growand die, decaying material builds up. This, along with the slowbreakdown of rocks, builds soil. When enough soil has formed,other organisms can move into the area.

Why are pioneer plant species important in disturbed environments?

Figure 8 Mosses can grow inthe thin layer of soil that coversthese rocks.

Measuring WaterAbsorption by a MossProcedure

1. Complete a safety worksheet.

2. Weigh a self-sealing plas-tic bag and then place ahandful of Sphagnum mossinto it. Wash your handsafter handling the moss.

3. Weigh the bag and mossand then calculate theweight of the moss.

4. Pour 200 mL of room-temperature water intothe bag and seal it. Place the bag on thecounter for 15 minutes.

5. Hold the bag over a con-tainer, and use scissors tocut off about one-half inchof one corner. Allow theunabsorbed water to drain from the bag into the container.

6. Measure the amount ofwater in the container.

Analysis1. In your Science Journal, cal-

culate the amount of waterabsorbed by the moss.

2. What is the amount ofwater absorbed per unit ofmoss weight?

SC.H.1.3.5

Michael P. Gadomski/Photo Researchers

356 CHAPTER 12 Classifying Plants

Seedless Vascular PlantsFerns and mosses are alike in one way. Both reproduce by

spores instead of seeds. However, ferns, like the one in Figure 9,are different from mosses because they have vascular tissue. Thevascular tissue in seedless vascular plants, like ferns, is made up oflong, tubelike cells. These cells carry water, minerals, and food tocells throughout the plant. Why is vascular tissue an advantage toa plant? Nonvascular plants like the moss are usually only a fewcells thick. Each cell absorbs water directly from its environment.As a result, these plants cannot grow large. Vascular plants, on theother hand, can grow bigger and thicker because the vascular tis-sue distributes water and nutrients to all plant cells.

What is the value of rain forests?

Deforested annually (km2)more than 15,0002,000 to 14,800100 to 1,900

Topic: Florida FernsVisit fl7.msscience.com for Weblinks to information about fernsnative to Florida.

Activity In your Science Journal,list three native fern species.Describe the growing conditionsfor each species.

Throughout history, cultures have usedplants for medicines. Some cultures used

willow bark to cure headaches. Willow barkcontains salicylates (suh LIH suh layts), themain ingredient in aspirin. Heart problemswere treated with foxglove, which is themain source of digitalis (dih juh TAH lus), adrug prescribed for heart problems. Have allmedicinal plants been identified?

Identifying the Problem Tropical rain forests have the largest

variety of organisms on Earth. Many plantspecies are still unknown. These forests arebeing destroyed rapidly. The map below showsthe rate of destruction of the rain forests.

Some scientists estimate that most tropicalrain forests will be destroyed in 30 years.

Solving the Problem1. What country has the most rain forest

destroyed each year? 2. Where can scientists go to study rain

forest plants before the plants aredestroyed?

3. Predict how the destruction of rainforests might affect research on newdrugs from plants.

LA.B.2.3.4

LA.A.1.3.4

SECTION 2 Seedless Plants 357

Types of Seedless Vascular PlantsBesides ferns, seedless vascular plantsinclude ground pines, spike mosses, andhorsetails. About 1,000 species of groundpines, spike mosses, and horsetails areknown to exist. Ferns are more abundant,with at least 12,000 known species. Manyspecies of seedless vascular plants are knownonly from fossils. They flourished during thewarm, moist period 360 million to 286 mil-lion years ago. Fossil records show that somehorsetails grew 15 m tall, unlike modernspecies, which grow only 1 m to 2 m tall.

Ferns The largest group of seedless vascu-lar plants is the ferns. They include manydifferent forms, as shown in Figure 10. They have stems, leaves,and roots. Fern leaves are called fronds. Ferns produce spores instructures that usually are found on the underside of theirfronds. Thousands of species of ferns now grow on Earth, butmany more existed long ago. From clues left in rock layers, sci-entists infer that about 360 million years ago much of Earth wastropical. Steamy swamps covered large areas. The tallest plantswere species of ferns. The ancient ferns grew as tall as 25 m—taller than the tallest fern species alive today. Most mod-ern tree ferns are about 3 m to 5 m in height and grow in trop-ical regions of the world.

Figure 9 Mosses and ferns areseedless plants and grow in similarenvironments. Explain why ferns can grow tallerthan mosses.

Figure 10 Ferns have manydifferent shapes and sizes.

The sword fern has a typical fernshape. Spores are produced in struc-tures on the back of the frond.

This fern grows on other plants, not in the soil. Infer why it’s called the staghorn fern.

Tree ferns grow in tropical areas.

(t)Farrell Grehan/Photo Researchers, (bl)Steve Solum/Bruce Coleman, Inc., (bc)R. Van Nostrand/Photo Researchers, (br) Inga Spence/Visuals Unlimited

Club Mosses Ground pines and spike mosses aregroups of plants that often are called club mosses.They are related more closely to ferns than to mosses. These seedless vascular plants have needle-like leaves. Spores are produced at the end of thestems in structures that look like tiny pine cones.Ground pines, shown in Figure 11, are found fromarctic regions to the tropics, but rarely in large num-bers. In some areas, they are endangered becausethey have been over collected to make wreaths andother decorations.

Where are spores in club mossesproduced?

Spike mosses resemble ground pines. One species of spikemoss, the resurrection plant, is adapted to desert conditions.When water is scarce, the plant curls up and seems dead. Whenwater becomes available, the resurrection plant unfurls its greenleaves and begins making food again. The plant can repeat thisprocess whenever necessary.

Horsetails The stem structure of horsetails is unique amongthe vascular plants. The stem is jointed and has a hollow centersurrounded by a ring of vascular tissue. At each joint, leavesgrow out from around the stem. In Figure 12, you can see thesejoints. If you pull on a horsetail stem, it will pop apart in sec-tions. Like the club mosses, spores from horsetails are producedin a conelike structure at the tips of some stems. The stems ofthe horsetails contain silica, a gritty substance found in sand.For centuries, horsetails have been used for polishing objects,sharpening tools, and scouring cooking utensils. Another com-mon name for a horsetail is scouring rush.

Importance of Seedless Plants

When many ancient seedless plants died,they became submerged in water and mudbefore they decomposed. As this plant mate-rial built up, it became compacted and com-pressed and eventually turned into coal—aprocess that took millions of years.

Today, a similar process is taking place inbogs, which are poorly drained areas of landthat contain decaying plants. The plants in bogsare mostly seedless plants like mosses and ferns.

Figure 12 Most horsetails growin damp areas and are less than 1 m tall.Identify where spores would beproduced on this plant.

Figure 11 Photographers onceused the dry, flammable spores ofclub mosses as flash powder. Itburned rapidly and produced thebright light needed to take photographs.

(t)Jo

y Sp

urr/B

ruce

Col

eman

, Inc

., (b

)W.H

. Bla

ck/B

ruce

Col

eman

, Inc

.

6. Use Fractions Approximately 8,000 species of liver-worts and 9,000 species of mosses exist today.Estimate what fraction of these seedless nonvascularplants are mosses.

SummarySeedless Nonvascular Plants

• Seedless nonvascular plants include mosses,liverworts, and hornworts.

• They are usually only a few cells thick and nomore than a few centimeters tall.

• They produce spores rather than seeds.

Seedless Vascular Plants

• Seedless vascular plants include ferns, clubmosses, and horsetails.

• Vascular plants grow taller and can live fartherfrom water than nonvascular plants.

Importance of Seedless Plants

• Nonvascular plants help build new soil.

• Coal deposits formed from ancient seedlessplants that were buried in water and mudbefore they began to decay.

Self Check1. Compare and contrast the characteristics of mosses

and ferns.

2. Explain what fossil records tell about seedless plantsthat lived on Earth long ago.

3. Identify growing conditions in which you would expectto find pioneer plants such as mosses and liverworts.

4. Summarize the functions of vascular tissues.

5. Think Critically The electricity that you use every daymight be produced by burning coal. What is the con-nection between electricity production and seedlessvascular plants?

SECTION 2 Seedless Plants 359

Peat When bog plants die, the waterlogged soilslows the decay process. Over time, these decayingplants are compressed into a substance called peat.Peat, which forms from the remains of sphagnummoss, is mined from bogs, as shown in Figure 13,to use as a low-cost fuel in places such as Irelandand Russia. Peat supplies about one-third ofIreland’s energy requirements. Scientists hypothe-size that over time, if additional layers of soil bury,compact, and compress the peat, it will become coal.

Uses of Seedless Vascular Plants Manypeople keep ferns as houseplants. Ferns also are soldwidely as landscape plants for shady areas. Peat andsphagnum mosses also are used for gardening. Peatis an excellent soil conditioner, and sphagnummoss often is used to line hanging baskets. Ferns also are used asweaving material for basketry.

Although most mosses are not used for food, parts of manyother seedless vascular plants can be eaten. The rhizomes andyoung fronds of some ferns are edible. The dried stems of one typeof horsetail can be ground into flour. Seedless plants have beenused as folk medicines for hundreds of years. For example, fernshave been used to treat bee stings, burns, fevers, and even dandruff.

Figure 13 Peat is cut from bogsand used for a fuel in some parts ofEurope.

More Section Review fl7.msscience.com

SC.F.2.3.4

SC.F.1.3.1

MA.A.1.3.1

Farrell Grehan/Photo Researchers