The Plant KingdomNon-vascular plants – the mossess

&Seedless Vascular plants – the ferns

• 1.2 billion years ago (BYA) – appearance of cyanobacteria on land• 500 million years ago (MYA) – appearance of plants, fungi and animals• more than 290,000 known plant species today• plants inhabit all but the harshest environments

– such as some mountaintops, deserts areas and polar regions

• many plants have returned to their aquatic “roots”– e.g. some species of sea grasses

• most present-day plants are terrestrial• presence of plants has enabled other life forms to survive on land

– through their production of O2

Adaptations by Land plants

• plants evolved from algae• advantages of a terrestrial life:

– stronger exposure to sunlight for photosynthesis– atmosphere offered more CO2 for photosynthesis– soil rich in nutrients– initially relatively few herbivores

• movement onto land would require protection of the zygote from drying out

• movement onto land resulted in the development of specific adaptations– facilitated survival and reproduction on land– e.g. development of a structural system to withstand the forces of gravity– e.g. changes adapting to the relative scarcity of water

• botanists do not use the term phyla when classifying the plant kingdom – use divisions

• currently accepted organization: development of two lineages or divisions: non-vascular and vascular (390 MYA)

• called the Bryophyta (non-vascular) and Tracheophyta (vascular)

Classifying the Plant Kingdom

** plants can be divided into 2major categories1. non-vascular2. vascular – subdivided into 2 more categories:

a. seedlessb. seed

Non-Vascular Plants

• Bryophytes: term used to refer to all non-vascular plants– do not have a single ancestor– known popularly as the mosses,

liverworts and hornworts– is a debate as to how they are

related to each other and how they evolved

– don’t possess the advanced adaptations of vascular plants (e.g. roots & leaves)

Ancestralgreen alga

Origin of land plants(about 475 mya)

Origin of vascular plants(about 420 mya)

Origin of seed plants(about 360 mya)

Land plants

Vascular plants

Seed plantsSeedless vascular plantsBryophytes

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Non-vascular plants

• the bryophytes are made up of 3 phyla

• three phyla:– 1. Phylum Hepatophyta: liverworts

• e.g. Marchantia– 2. Phylum Anthocerophyta –

hornworts– 3. Phylum Bryophyta – mosses

e.g. Mnium Marchantia polymorpha = liverwort

Plagiochila deltoidea = liverwort

Non-vascular plants: Mosses

• moss life cycle is dominated by the gametophyte stage– gamete forming stage– anchored to the ground by rhizoids – long tubular single cells– NOT roots – not composed of tissues (cells only), lack specialized conducting cells and

are not responsible for water and mineral absorption• some mosses are NOT mosses at all – Irish moss (red seaweed), reindeer moss

(lichen), club mosses (seedless vascular plant)

the gametophyte of mossesis the actual moss!!

Alternation of Generations in Plants• life cycle of a moss alternates between a multi-cellular

gametophyte (n) and a multi-cellular sporophyte (2n) • This alternation is known as ALTERNATION OF GENERATIONS

Bryophyte General Life Cycle• The Gametophyte is haploid and makes haploid gametes by MITOSIS• The gametes fuse to make a diploid Zygote (fertilization)• The zygote develops into a multi-cellular Sporophyte by mitosis• The Sporophyte is diploid and makes spores by MEIOSIS• The spores germinate into new Gametophytes

the gametophyte the mossis the actual moss!!

The Moss Gametophyte• located in the gametophyte are the reproductive structures that make the

gametes = gametangia (singular = gametangium)• male gametangium – antheridium (plural = antheridia)

– makes sperm by mitosis• female gametangium – archegonium (plural = archegonia)

– makes eggs by mitosis

antheridium gametangium with sperm

archegonium gametangium

egg

production of the gametes is by mitosis since the gametophyte is haploid already!!!

The Moss Sporophyte• the sporophyte is very small in the non-vascular plant• fertilization is followed by development of the embryo within the archegonium• the embryo develops into a small sporophyte (diploid) - remains attached to the

archegonium for absorption of nutrients• the sporophyte is comprised of:

– 1. seta (stalk) – 2. sporangium surrounded by a capsule

• haploid spores develop in this sporangium via meiosis

moss

Seedless Vascular Plants

• bryophytes prominent during the first 100 million years of plant evolution– but they are not very tall– rarely over 20 cm in height

• those plants that could achieve heights would have better access to sunlight, better spore dispersal

• height would mean the need for a transport system for water and nutrients

• would also need a structural support system• ferns are example of the evolution of plants that began to

develop height and a vascular system• fossils of present day vascular plants date back 425 MYA!!!

Seedless Vascular plants

• two clades: – Phylum Lycophyta and Phylum Pterophyta

• both have modified leaves called sporophylls that bear sporangia for making spores

• two types of sporophylls: microphylls and megaphylls• microphyll – needle-like• megaphyll – e.g. fern frond

Seedless Vascular plants

• Phylum Pterophyta – ferns, horsetails and whisk ferns– the pterophytes are divided by some botanists into separate phyla:

• phylum Sphenophyta – horsetails• phylum Psilophyta – whisk ferns and relatives• phylum Pterophyta – ferns

Equisetum – horsetail fern Psilotum – whisk fern

Seedless Vascular plants

• Phylum Lycophyta – club mosses, spike mosses and quillworts– examples of small sporophylls called microphylls

Club mossSelaginella

QuillwortIsoetes

Phylum Pterophyta• ferns

– leaves are known as megaphylls– fern sporophyte is comprised of underground,

horizontal stems called rhizomes – from these come vertical shoots that give rise to

large megaphylls called fronds – frond is divided into pinna (or leaflets)– frond grows as the fiddlehead– megaphyll is a compound leaf with a center

rachis and multiple pinna• the pinna itself may be may up of small pinnules

– although some fern species – e.g. staghorn fern – have a simple leaf structure

mature frond is called a megaphyll

– gametophyte is underground and very small– dies after the young sporophyte fern begins to develop– the sporophyte is diploid & bears sporangia (singular = sporangium) – sporangia are clustered under the frond in structures called sori (singular

= sorus)– one sorus is made up of multiple sporangia

Phylum Pterophyta

the fern is the sporophyte

Spore

Sperm

Antheridium

Egg

Haploid (n)Diploid (2n)

Key

Younggametophyte

Sorus

Sporangium

MEIOSIS

FERTILIZATION

Archegonium

Zygote

Newsporophyte

Maturesporophyte

Sporangium

Gametophyte

Fiddlehead

Fern Life Cycle• in the mature fern (the sporophyte) – presence of multiple sori - each

comprised of many sporangia • inside each sporangium – meiosis haploid spore production• spores released from the sori • land on moist soil germination into the gametophyte

• most fern gametophytes

are dieocious – bothmale and female gametangia

Fern Life Cycle• bisexual gametophyte develops male and female gametangia

– male antheridium – for sperm production– female archegonium - for egg development

• sperm are released and swim to the egg within the archegonium – fertilization and development into a diploid zygote

Fern Life Cycle

• the zygote develops into a new diploid sporophyte – emerges from the gametophyte

• growth of the sporophyte produces the fern – young, developing frond is called the fiddlehead

• gametophyte disappears• fronds develop sporangia for the production of spores (via meiosis)

http://www.youtube.com/watch?v=9c9Zi3WFVRc