The Plant Kingdom: Flowering Plants Chapter 25

LEARNING OBJECTIVE 1 Summarize the features that distinguish flowering plants from gymnosperms

KEY TERMS ANGIOSPERM Traditional name for flowering plants A large, diverse phylum of plants that form flowers for sexual reproduction and produce seeds enclosed in fruits

Flowering Plants Like gymnosperms: Unlike gymnosperms: Flowering plants have vascular tissues and produce seeds Unlike gymnosperms: Ovules of flowering plants are enclosed within an ovary

KEY TERMS OVULE Structure in the ovary that contains a female gametophyte and develops into a seed after fertilization OVARY Base of a carpel or fused carpels that contains ovules and develops into a fruit after fertilization

Orange Fruit Development

LEARNING OBJECTIVE 2 Describe the ecological and economic significance of the flowering plants

Ecology and Economy Our survival as a species depends on flowering plants Major food crops Products Cork, rubber, tobacco, coffee, chocolate, aromatic oils for perfumes Valuable lumber Fibers and medicines

Economic Botany Subdiscipline of botany that deals with plants of economic importance Most of these are flowering plants

LEARNING OBJECTIVE 3 Distinguish between monocots and eudicots, the two largest classes of flowering plants Give specific examples of each class

KEY TERMS COTYLEDON The seed leaf of a plant embryo, which may contain food stored for germination

KEY TERMS MONOCOT One of two main classes of flowering plants; monocot seeds contain a single cotyledon Monocots have floral parts in threes Monocots include grasses, orchids, irises, onions, lilies, palms

KEY TERMS EUDICOT One of two main classes of flowering plants; eudicot seeds contain two cotyledons Eudicots have floral parts in fours or fives Eudicots include oaks, roses, mustards, cacti, blueberries, sunflowers

Monocots and Eudicots

(a) Monocots, such as this nodding trillium Petal Sepal Anther of stamen Stigmas of pistil Figure 25.2: The two largest classes of flowering plants. (a) Monocots, such as this nodding trillium (Trillium cernuum), have their floral parts in threes. Note the three green sepals, three white petals, six stamens, and three stigmas (the compound pistil consists of three fused carpels). Fig. 25-2a, p. 488

(b) Most eudicots such as this Tacitus Petal Anther of stamen Pistils Figure 25.2: The two largest classes of flowering plants. (b) Most eudicots such as this Tacitus bellus have floral parts in fours or fives. Note the five petals, 10 stamens, and five separate pistils. Five sepals are also present but barely visible against the background. Fig. 25-2b, p. 488

LEARNING OBJECTIVE 4 Briefly explain the life cycle of a flowering plant Describe double fertilization

Life Cycle Flowering plants undergo an alternation of generations: Sporophyte generation is larger and nutritionally independent Gametophyte generation is reduced to only a few microscopic cells

KEY TERMS DOUBLE FERTILIZATION A process in the flowering plant life cycle in which there are two fertilizations One results in formation of a zygote Second results in formation of endosperm

KEY TERMS ENDOSPERM The 3n nutritive tissue formed at some point in the development of all angiosperm seeds

Life Cycle: Flowering Plants

6 5 3 7 2 4 8 1 Pollination Developing pollen tube of mature male gametophyte Each microspore develops into a pollen grain 6 Embryo sac (mature female gametophyte) 5 Pollen grain (immature male gametophyte) Microspore Tetrad of microspores Pollen tube 3 Polar nuclei Megaspore Egg nucleus Two sperm cells HAPLOID (n) GAMETOPHYTE GENERATION Meiosis Ovary Double fertilization DIPLOID (2n) SPOROPHYTE GENERATION Megaspore mother cell Endosperm (3n) 7 2 4 Zygote (2n) Megasporangium (ovule) Figure 25.3: A generalized life cycle of flowering plants. The most distinctive feature of the flowering plant life cycle is double fertilization, in which one sperm cell unites with the egg to form a zygote, and the other sperm cell unites with the two polar nuclei to form a 3n cell that gives rise to endosperm. See text for a detailed description. Fruit 8 Embryo Seed Microspore mother cells within microsporangia Seed coat 1 Seedling Anther Flower of mature sporophyte Fig. 25-3, p. 490

Pollen Grains

LEARNING OBJECTIVE 5 Discuss some of the evolutionary adaptations of flowering plants

Adaptations of Flowering Plants 1 Reproduce sexually by forming flowers Form seeds within fruits after double fertilization

Adaptations of Flowering Plants 2 Have efficient water-conducting vessel elements in xylem and carbohydrate-conducting sieve-tube elements in phloem Have pollen grains transported by wind, water, insects, other animals

KEY TERMS APOMIXIS A type of reproduction in which fruits and seeds are formed asexually

Adaptability of Flowering Plants

LEARNING OBJECTIVE 6 Trace the evolution of flowering plants from gymnosperms

Evolution of Flowering Plants Probably descended from ancient gymnosperms with specialized features leaves with broad, expanded blades and closed carpels Probably arose only once

Drimys piperita Carpel

(a) The carpel resembles a folded leaf in which the ovules borne on Fused margin Ovules Stigma Ovary Style Figure 25.6: Carpel of Drimys piperita. Stigma (a) The carpel resembles a folded leaf in which the ovules borne on its upper surface are enclosed. (b) A cross section of the carpel, cut along the dashed line in (a). Fig. 25-6, p. 493

Fossil Angiosperms

Pistils Scars on reproductive axis Carpel Ovule Figure 25.7: Fossil angiosperms. (a) The oldest known fossil angiosperm. This fossil of the extinct plant Archaefructus shows a carpel-bearing stem. It was discovered in northeastern China and is about 125 million years old. (b) The fossilized flower of the extinct plant Archaeanthus linnenbergeri, which lived about 100 mya. The scars on the reproductive axis (receptacle) may show where stamens, petals, and sepals were originally attached but abscised (fell off). Many spirally arranged pistils were still attached at the time this flower was fossilized. Fig. 25-7, p. 494

Evolution of Flowering Plants

Basal Angiosperms Core Angiosperms Evolution of vessel elements Amborella Water lilies Star anise Magnoliids Monocots Eudicots Evolution of vessel elements Evolution of flowering plants (a) One hypothesis of relationships among the flowering plants, based on fossil and molecular evidence. Amborella, water lilies, and star anise are living plants whose ancestors apparently branched off the angiosperm family tree early. These early groups were followed by the magnoliids, the monocot branch, and the eudicots. Figure 25.8: Evolution of flowering plants. Fig. 25-8, p. 495

LEARNING OBJECTIVE 7 Distinguish between basal angiosperms and core angiosperms

KEY TERMS BASAL ANGIOSPERM CORE ANGIOSPERM One of three groups of angiosperms thought to be ancestral to all other flowering plants CORE ANGIOSPERM Group including most angiosperm species Divided into three subgroups: magnoliids, monocots, and eudicots

KEY TERMS MAGNOLIID One of the groups of flowering plants Core angiosperms once classified as “dicots,” but molecular evidence indicates they are neither eudicots nor monocots Includes species in magnolia, laurel, and black pepper families, several related families

LEARNING OBJECTIVE 8 Briefly describe the distinguishing characteristics and give an example or two of each of the following flowering plant families: magnolia, walnut, cactus, mustard, rose, pea, potato, pumpkin, sunflower, grass, orchid, and agave

Flowering Plant Families 1 More than 300 families Magnolia family Important ornamentals and source of timber Examples: southern magnolia, tuliptree

Magnolia Family

Figure 25.9: The magnolia family. Fig. 25-9, p. 497

Flowering Plant Families 2 Walnut family Provides nuts for food, wood for furniture Examples: English walnut, black walnut, pecan Cactus family Important as ornamentals Examples: prickly pear, Christmas cactus

Walnut Family

Female flowers Catkin of male flowers Fruit (a drupe) Young tree Figure 25.10: The walnut family. Fruit (a drupe) Young tree Compound leaf Fruit with husk removed to show hard stone (a) The pinnately compound leaves and green fruits of black walnut (Juglans nigra) make the tree easy to recognize. Fig. 25-10a, p. 498

Figure 25.10: The walnut family. Fig. 25-10b, p. 498

Figure 25.10: The walnut family. Fig. 25-10c, p. 498

Cactus Family

(c) Cactus flowers contain numerous sepals, petals, and Stamens Stigma Petals Figure 25.11: The cactus family. (c) Cactus flowers contain numerous sepals, petals, and stamens. The compound pistil consists of two to many fused carpels. In this photo of a prickly pear cactus (Opuntia humifusa), the petals, stamens, and stigma are evident. Fig. 25-11c, p. 499

Flowering Plant Families 3 Mustard family Many important food crops Examples: cabbage, broccoli, cauliflower, turnip, mustard Rose family Commercially important fruits and ornamentals Examples: apple, pear, plum, cherry, apricot, peach, strawberry, raspberry, rose

Mustard Family

(a) A typical mustard flower, showing the Pistil Stamen Petal Figure 25.12: The mustard family. Sepal (a) A typical mustard flower, showing the four petals arranged in the shape of a cross. Fig. 25-12a, p. 501

Mustard Family

Mustard Family

Mustard Family

Rose Family

Rose Family

Rose Family

Flowering Plant Families 4 Pea family Important food crops Examples: garden pea, chick pea, green bean, soybean, lima bean, peanut, red clover, alfalfa

Pea Family

(b) Close-up of a bean flower, showing its irregular corolla shape. Compound leaf (three leaflets) Banner Young fruit Wing Sepal Corolla Keel (two fused petals) (b) Close-up of a bean flower, showing its irregular corolla shape. Pod (fruit) Remnants of stigma and style Seeds Remnants of sepals (and sometimes petals and stamens) Figure 25.14: The pea family. (c) The bean fruit, a legume, is opened to show the seeds. (a) Part of a common bean (Phaseolus vulgaris) plant, showing flowers and developing fruits. Fig. 25-14a-c, p. 503

Pea Family

Pea Family

Flowering Plant Families 5 Potato family Important food crops and chemicals used as drugs Examples: potato, tomato, green pepper, eggplant, petunia, deadly nightshade (belladonna)

Potato Family

Flowering Plant Families 6 Pumpkin family Food crops Examples: pumpkins, melons, squashes, cucumbers, cantaloupe, honeydew, muskmelon, cucumber, watermelon

Pumpkin Family

(a) Cutaway view of a female squash flower. Note Petals fused into bell shape Stigma Style Ovary Figure 25.16: The pumpkin family. (a) Cutaway view of a female squash flower. Note the inferior ovary located beneath the point of attachment of the sepals and petals. Fig. 25-16a, p. 505

Pumpkin Family

(b) Cutaway view of a male squash flower. Note the united anthers. Figure 25.16: The pumpkin family. (b) Cutaway view of a male squash flower. Note the united anthers. Fig. 25-16b, p. 505

Pumpkin Family

Flowering Plant Families 7 Sunflower family One of the largest families of flowering plants Examples: chrysanthemums, marigolds, sunflowers, daisies, and some food plants such as lettuce, globe artichokes

Sunflower Family

a) Head of a sunflower (Helianthus annuus). Ray floret Disc floret Figure 25.17: The sunflower family. a) Head of a sunflower (Helianthus annuus). Fig. 25-17a, p. 506

(d) Bisexual disc floret. Ray floret Disc floret Stigmas Anther Corolla Figure 25.17: The sunflower family. Ovary (c) Female ray floret. (d) Bisexual disc floret. Fig. 25-17cd, p. 506

Flowering Plant Families 8 Grass family Most important family of flowering plants from the human standpoint Examples: rice, wheat, corn, oats, barley, rye, sugarcane, bamboo

Grass Family

are wind pollinated, are highly modified. Note, for example, the long, Anther Inflorescence Palea Filament Feathery stigma Ovary Blade Reduced petals Sheath Lemma Stolon Rhizome Figure 25.18: The grass family. Fibrous root system (a) The growth habit of a representative grass plant. Grass flowers, which are wind pollinated, are highly modified. Note, for example, the long, feathery stigmas, adapted to efficiently catch wind-borne pollen. Fig. 25-18a, p. 507

Flowering Plant Families 9 Orchid family One of the largest families of flowering plants; contains a greater variety of flowers than any other family Example: the vanilla orchid Agave family Best known for ornamentals Examples: century plant, sisal hemp, bowstring hemp

Orchid Family

(a) The moth orchid (Phalaenopsis hybrid) Aerial roots Figure 25.19: The orchid family. (a) The moth orchid (Phalaenopsis hybrid) has photosynthetic aerial roots. Fig. 25-19a, p. 509

(b) A Cymbidium hybrid has pseudobulbs Figure 25.19: The orchid family. (b) A Cymbidium hybrid has pseudobulbs that function as storage organs. Fig. 25-19b, p. 509

(c) Orchid flowers, such as Dendrobium, are Petal Sepal Lip (modified petal) Figure 25.19: The orchid family. (c) Orchid flowers, such as Dendrobium, are distinctive in that the third petal forms a lip. Fig. 25-19c, p. 509

Agave Family

Animation: Monocot Life Cycle CLICK TO PLAY