How Plants Colonized Land
 For the first 3 billion years of Earth’s history, the terrestrial surface was lifeless
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About 500 million years ago plants, fungi, and animals began existing on land
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There are about 290,000 living species of land plants
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Plants have enabled other life-forms to survive on land because they supply our atmosphere with oxygen, stabilize landscapes, and are the ultimate providers of food.
29.1: Land Plants evolved from green algae
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The green algae called charophyceans are the closest relatives of land plants
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Plants and protists (especially green algae) share many characteristics, including that they are: multicellular, eukaryotic, photosynthetic autotrophs, have cell walls of cellulose, and have chlorophylls a and b .
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There are four key characteristics that plants only share with the charophyceans, however.
1.
Rose-shaped complexes for cellulose synthesis (See Figure 29.2 page 574)
2.
Peroxisome enzymes
3.
Similar structure of the flagellated sperm
4.
Formation of a phragmoplast , which is an alignment of cytoskeletal elements and Golgiderived vesicles across the midline of the dividing cell.
 An international study called “Deep Green” has shown that plants and charophyceans share similar nuclear and chloroplast genes.
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Finally, charophyceans have a durable polymer layer called sporopollenin that helps prevent their zygotes from drying out. An ancestral form of sporopollenin may have been the precursor to the tough walls that encase plant spores. This polymer layer allowed plants to live above the waterline.
29.2: Land Plants possess a set of derived terrestrial adaptations
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The dividing line between plants and algae is a bit fuzzy, but most scientists group plants with the embryophytes (See Figure 29.4, page 575)
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There are five key traits that appear in nearly all land plants that are not found in the charophyceans (See Figure 29.5, pages 576-577):
1.
Apical Meristems
2.
Alternation of Generations
3.
Walled spores produced in sporangia
4.
Multicellular gametangia
5.
Multicellular and dependent embryos
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Other key traits found in many land plants include:
1.
An epidermal covering called a cuticle that prevents plants from desiccation (drying out)
2.
Secondary compounds-chemicals such as alkaloids, terpenes, tannins, flavenoids, and phenolics that help plants defend against predators and parasites.

The precise age of plants is still undecided, although many estimate that they are between
475-700 million years old, based on fossil evidence (Figure 29.6, pg 578)
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There are currently Ten Phyla of extant plants (See Table 29.1 on page 578 and Figure 29.7 on page 579 for GREAT INFORMATION)

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Plants are divided into major groups: o Vascular Tissue (Xylem and Phloem)-Vascular Plants
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Seed Plants-have an embryo packaged with a supply of nutrients inside a protective coat
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Angiosperms: Flowering plants (Roses)
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Gymnosperms: Naked seed plants (Conifers)
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Seedless Vascular Plants-Lycophytes and pterophytes o Non-Vascular Tissue-Bryophytes (Liverworts, Hornworts, and Mosses)
29.3: The life cycles of mosses and other bryophytes are dominated by the gametophyte stage

There are three major phyla of Bryophytes (See Figure 29.9, page 582):
1.
Liverworts (Hepatophyta): Gametophytes are liver-shaped
2.
Hornworts (Anthocerophyta): Gametophytes grow horizontally & Sporophyte stage resembles a blade of grass
3.
Mosses (Bryophyta): Gametophytes grow vertically
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Bryophyte gametophytes are larger and longer-living than sporophytes (See Fig. 29.8, pg.
581)
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Mosses are found around the world. They are very versatile because of their lightweight spores. They are common in forests and wetlands, but they are also found on mountaintops, in the tundra, and deserts.
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Peat moss can form widespread deposits of partially decayed organic material called peat.
Peat bogs can preserve mummified corpses for thousands of years and they store 400 billion tons of organic carbon to stabilize atmospheric levels of CO
2
. Peat is also used as a fuel source and soil conditioner (See Figure 29.10, page 583).
29.4: Ferns and other seedless vascular plants formed the first forests
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Vascular plants dominate most landscapes today
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Vascular plants truly diversified during the Carboniferous period
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Vascular plants have key characteristics:
1.
Life Cycles with dominant Sporophytes (See Figure 29.12, page 585)
2.
Transport in Xylem and Phloem: a.
Xylem conducts water and minerals. Xylem contains tracheids , which are tubeshaped cells that carry material up from the roots. Tracheids are dead cells with walls strengthened by lignen . b.
Phloem is living sugar-conducting cells arranged into tubes. Phloem transports sugars, amino acids, and other organic products from the shoots to the roots.
3.
Roots: organs that anchor vascular plants and enable them to absorb water and nutrients from the soil.
4.
Leaves: organs that increase the surface area of vascular plants, which allow plants to capture more cellular energy for photosynthesis (Fig. 29.13, page 586). a.
Microphylls : small spine-shaped leaves with a single vein (found in lycophytes) b.
Megaphylls: large leaves with a highly branched vascular system
5.
Sporophylls : modified leaves that bear sporangia a.
Sori : fern sporophylls made of clusters of sporangia b.
Strobili : lycophytes and gymnosperm sporophylls that form cones

Spore Production (Page 586): a.
Homosporous : have one type of sporophyll producing one type of spore b.
Heterosporous: has two types of sporophyll and produces two types of spores
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There are two Clades of Seedless Vascular Plants (See Figure 29.14, page 587)
1.
Lycophyta: Club Mosses, Spike mosses, and Quillworts. They are the most primitive of the vascular plants. Many grow on trees as epiphytes (plants that use other plants as a substrate but are not parasites).
2.
Pterophyta: Ferns, Horsetails, and Whisk Ferns (See Figure 29.14, page 587) Ferns are the most widespread seedless vascular plants (they even made the cover of your book

)

During the Carboniferous Period, seedless vascular plants formed the first forests (Figure
29.15, page 588). These plants accelerated the rate of photosynthesis, which greatly dropped the level of CO
2 in the atmosphere. These first forests eventually formed coal (a critical fossil fuel whose burning has contributed to Global Warming)
The Evolution of Seed Plants

Fossils and studies of living plants show that the origin of seed plants occurred some 360 million years ago.
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Seeds enabled plants to become the dominant producers in most of the terrestrial ecosystems and to make up the vast majority of plant biodiversity
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The domestication of seed plants has helped create a dominant human society
30.1: The reduced gametophytes of seed plants are protected in ovules and pollen grains
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There are five common characteristics of seed plants:
1.
Reduced Gametophyte: The tiny gametophytes can develop from spores held inside the sporangia of the parental sporophyte. This protects the female gametophyte from environmental stresses, such as drought and UV radiation. It also provides the gametophyte with nutrients (See Figure 30.2 page 592 for the evolution of gametophyte/sporophyte relationship)
2.
Heterospory: Seed plants are heterosporous. The megasporangia in megasporophylls produce megaspores which give rise to female gametophytes. The microsporangia in microsporophylls produce microspores that give rise to the male gametophyte.
3.
Ovules: Seed plants retain the megaspore within the parent sporophyte. Layers of sporophyte tissue called integuments surround and protect the megasporangium. The megasporangium, megaspore and their integument is called an ovule (Fig. 30.3, pg. 593)
4.
Pollen: Microspores develop into pollen grains, which contain the male gametophytes of seed plants. Protected by a tough coat containing sporopollenin, pollen grains can be carried away from their parent plant by wind, animals, etc. The transfer of pollen to the part of a seed plant containing ovules is called pollination . The sperm of seed plants to not require water or flagella to move toward the female gametophyte, which is a key adaptation for life on land.
5.
Seeds: A seed consists of the embryo, along with a food supply, packaged within a protective coat derived from the integuments. A seed forms when sperm fertilizes the egg of a seed plant and the zygote grows into the embryo. Seeds allowed plants to resist harsh environments and to disperse more widely. Because seeds are multicellular, they are very complex and can remain dormant for long periods of time.

30.2: Gymnosperms bear “naked” seeds, typically on cones
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Gymnosperm seeds are exposed on modified leaves that usually form cones (strobili)
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Gymnosperms include conifers (trees such as pines, firs, and redwoods).
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There are four phyla of gymnosperms (See pages 594-595):
1.
Cycadophyta: Large cones and palmlike leaves, they dominated the Mesozoic era
2.
Ginkophyta: Only one known species, Ginkgo biloba . The ginko has fanlike leaves that turn gold in autumn and these trees are very tolerant of air pollution.
3.
Gnetophyta: Contains three genera: Gnetum , Ephedra, and Welwitschia .
4.
Coniferophyta: The largest of the gymnosperm phyla, consisting of about 600 species of conifers. Most are evergreens and will retain their leaves throughout the year.
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The evolution of gymnosperms includes transitional species of seedless vascular plants called progymnosperms . These appear in the fossil record about 360 million years ago (Fig.
30.5, page 596).
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The life cycle of the pine tree is characteristic of gymnosperms (Figure 30.6, page 597)
30.3: The reproductive adaptations of angiosperms include flowers and fruits
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Angiosperms are the most diverse and widespread of all plants, with more than 250,000 species (about 90% of all plant species)
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All angiosperms are classified in the phylum Anthophyta
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The two main characteristics of angiosperms are flowers and fruit.
1.
Flowers: Structures specialized for sexual reproduction. A flower is a specialized shoot that can have up to four rings of modified leaves called floral organs (Fig. 30.7, pg 598): a.
Sepals : green and enclose the flower before it opens b.
Petals : brightly colored and aid in attracting pollinators c.
Stamens : Microsporophylls that give rise to pollen grains containing the male gametophytes. A stamen consists of a stalk called the filament and a terminal sac called the anther where pollen is produced. d.
Carpels : Megasporophylls which make megaspores and the female gametophytes. The tip of the carpel is a sticky stigma that receives pollen. A style leads to the ovary at the base of the carpel, which contains one or more ovules. A single carpel or a group of fused carpels is sometimes called a pistil .
***The whorls of flower organs are attached to a part of the stem called the receptacle.
2.
Fruits: A fruit typically consists of a mature ovary (Figure 30.8, page 599). The fruit begins to develop after pollination. The wall of the ovary becomes the pericarp , the thickened wall of the fruit. Mature fruits can be fleshy (oranges, strawberries, and grapes) or dry (beans, nuts, and grains). Fruit adaptations are used to disperse seeds (by wind, water, or animals). Animals will often eat the fruit, digest the fleshy part, and deposit the seeds (with a supply of fertilizer) miles from where the fruit was eaten.
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A typical angiosperm life cycle is shown in Figure 30.10, page 600. Within the anther, the male gametophytes are pollen grains. The pollen is carried to the stigma at the tip of the carpel. The pollen grain germinates and grows a tube that extends into the style and reaches the ovary, penetrating through a pore called the micropyle . The ovules have developed inside the ovary and contain the female gametophyte, called the embryo sac.
The embryo sac consists of only a few cells, one of which is the egg. The pollen tube discharges two sperm cells into the embryo sac. One fuses with the egg and the other fuses with two nuclei in the center of the embryo sac (forming a triploid nucleus). This is known as double fertilization. The ovule will mature into a seed. The zygote develops into a sporophyte

embryo with cotyledons (seed leaves: one seed leaf = monocot, two seed leaves = dicot).
The triploid nucleus gives rise to the endosperm , which is rich in starch and other food reserves.

Many plants undergo cross-pollination (the transfer of pollen from an anther of a flower on one plant to the stigma of a flower on another plant of the same species) which creates genetic variation.
Angiosperm Evolution:

Angiosperms originated at least 140 million years ago

Some fossils of angiosperms have been found (‘proto-angiosperms’ See Fig. 30.11 pg. 601).
 Botanist Michael Frohlich uses the “evo-devo” approach to say that the ancestor of angiosperms had separate pollen-producing and ovule-producing structures. As a result of a mutation, ovules developed on some microsporophylls, which evolved into carpels.
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Much remains unknown about angiosperm evolution . . .
Angiosperm Diversity:

Traditionally, most plants were divided into two groups (monocots and dicots). Current research shows that there are four groups: the monocots, eudicots, basal angiosperms, and magnolids (See Figure 30.12, page 602-603)
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Monocots and Eudicots Compared (page 603):
Monocots Eudicots
One cotyledon
Fibrous Roots
Parallel Veins
Scattered Vascular Tissue
Pollen grain w/one opening
Flowers in multiples of 3
Two cotyledons
Netlike Veins
Ringed Vascular Tissue
Taproot
Pollen grain w/three openings
Flowers in multiples of four or five
Links Between Animals and Angiosperms
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Plant-pollinator relationships have likely played a role in increasing both angiosperm and animal diversity (See Figure 30.13, page 604). This coevolution of organisms has been a powerful influence on our environment.
30.4: Human welfare depends greatly on seed plants
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No group is more important to our survival than seed plants→they are key sources of food, fuel, wood products, and medicine.
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Food: o Wheat, rice, maize, potatoes, cassava, and sweet potatoes yield 80% of the calories consumed by humans. . .WOW. o It takes 4.8 kilograms of grain to produce a kilogram of grain-fed beef o Tea and coffee are two of the world’s most popular beverages o The cacao tree gives us cocoa and chocolate (which makes for a better world) o Spices are key plant products as well!
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Medicine: About 25% of prescription drugs contain one or more active ingredients extracted from plants (See Table 30.1,page 605)
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THANK YOU PLANTS!