1

Overview of Plant Diversity

Chapter 29

2

The Evolutionary Origins of Plants• Defining characteristic of plants is protection of their

embryos. Land plants can be divided into two groups based on

the presence or absence of vascular tissue.

3

The Evolutionary Origins of Plants

• Adaptations to land– protected from desiccation - waxy cuticle

gas exchange- stomata– evolution of leaves increased

photosynthetic area

• Alternates Generations • diploid generation alternates with haploid

generation

4

Plant Life Cycles• diploid generation alternates with haploid

generation– diploid sporophyte produces haploid spores by meiosis

– Spores divide by mitosis, producing haploid gametophyte.

– haploid gametophyte is the source of gametes

– gametes fuse to form diploid zygote

5

Mosses, Liverworts, and Hornworts

• Bryophytes - avascular plants– sporophytes are attached to and

nutritionally dependent on gametophytes– require water to reproduce sexually– most are small

6

Features of Vascular Plants

• Vascular tissues– xylem– phloem

– Earliest vascular plants lacked seeds

Seedless Vascular Plants - Ferns

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• Ferns are the most abundant group of seedless vascular plants.

– greater development, independence, and dominance of fern’s Sporophyte

Fern sporophytes have underground stem, the rhizome.sporangia in clusters, sori, on back of frondsDiploid spore mother cells in each sporangium undergo meiosis, producing haploid spores

8

Seed Plants• Seed Plants first appeared about 425 mya.

– drought protection– enhanced dispersal– dormant phase increase embryo survival

by waiting for favorable environmental conditions

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Gymnosperms• Seeds but lack flowers and fruits of

angiosperms• Four living groups

– conifers– cycads– gnetophytes– Ginkgo

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Angiosperms

• Ovules are enclosed within diploid tissues at time of pollination

– carpel, modified leaf encapsulating seed, develops into fruit

• Monocots and eudicots– eudicots and monocots differ in:

number of cotyledons leaf venation presence lateral meristems number of flower parts

12

13

Angiosperms

• Structure of flowers

14

Typical Angiosperm Lifecycle

polar nucleiegg

pollinationpollen pollen tubesperm

double fertilization zygote 2nendosperm 3n