The Plant Kingdom
Non-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
–
•
many plants have returned to their aquatic “roots”
–
•
•
such as some mountaintops, deserts areas and polar regions
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
Classifying the Plant Kingdom
• 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)
** plants can be divided into 2
major categories
1. non-vascular
2. vascular – subdivided into 2
more categories:
a. seedless
b. seed
Non-Vascular Plants
Land plants
Vascular plants
Origin of seed plants
(about 360 mya)
Origin of vascular plants
(about 420 mya)
Origin of land plants
(about 475 mya)
Ancestral
green alga
Angiosperms
Gymnosperms
Seedless vascular plants Seed plants
Pterophytes
Mosses
Hornworts
Liverworts
Charophyceans
– 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)
Bryophytes
Lycophytes
• Bryophytes: term used to refer to
all non-vascular plants
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
Plagiochila deltoidea = liverwort
Marchantia polymorpha = 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 mosses
is 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 moss
is 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
production of the gametes is by
mitosis since the gametophyte is
haploid already!!!
antheridium gametangium with
sperm
egg
archegonium gametangium
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 moss
Selaginella
Quillwort
Isoetes
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
Phylum Pterophyta
–
–
–
–
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
the fern is the sporophyte
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
Key
Haploid (n)
Diploid (2n)
Spore
Antheridium
Young
gametophyte
MEIOSIS
Sporangium
Sperm
Archegonium
Egg
Sporangium
Mature
sporophyte
New
sporophyte
Zygote
FERTILIZATION
Sorus
Gametophyte
Fiddlehead
• most fern
gametophytes
are dieocious – both
male 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