Evolution of Land Plants
Sources: Freeman (2002), Purves et al (2001)
Prior to the origin and diversitication of green plants in the mid-Silurian
(~450 mya), multicellular life was virtually entirely adapted to, and
confined to, aquatic lifestyles
Continental land Masses virtually unoccupied by multicellular organism –
multicellular-based ecosystems constituted tremendous potential for
adaptive radiation
Terrestrial life in a gaseous medium required evolutionary solutions to
structural, physiological and ecological challenges; Many of these
innovations can be regarded as exaptations of pre-existing traits of green
algae from which green plants diverged
Artist’s rendering of Carboniferous forest in a tropical river delta. Most of
the plants depicted here were nonseed tracheophytes 10 to 20 meters tall.
In the distance, early seed plants up to 40 meters tall towered over the
forest.
Sources: Freeman (2002), Purves et al (2001)
Kingdom Plantae is monophyletic assemblage,
descended from Green algae
Chlorophyll a and b are homogous in Chlorophyta,
Charaphyta and Plantae
Currently includes over 250,000 described species
classified in 12 monophyletic phyla
Most are terrestrial, some are secondarily aquatic
Ie, “true”
vasular
tissue
Diversification in plants involved successive
adaptive radiations following evolution of key
innovations that increased efficiency in a gaseous
(air) and solid (Earth) environment
Major problems were posed by gravity and by
water loss/availability
-maintain body structure in air (and with
increasing body size) – resist gravity
-obtain, transport and retain water
-fertilize eggs and produce and protect
embryos
Major evolutionary innovations included
Green algae of the lineage that includes Chara sp., are
most likely ancestors of plants. Copyright BPS.
-dimorphic body
-waxy cuticle and stomata
- true vascular tissue;
-life history dominated by sporophyte
generation
-jacketed sex organs; antheridia and archegonia
-seeds; embryo with nutritive tissue in
protective covering
-flowers; vehicles for pollination strategies
Sources: Freeman (2002), Purves et al (2001)
Sources: Freeman (2002), Purves et al (2001)
20
140
First extensive
grassland
First Flowering
Plant
First nectar-drinking
insects
First vessels
Carboniferous
(lycopods, seed ferns,
and horsetails
abundant)
280
360
410
1st seeds
1st vascular plant leaves
1st wood
1st roots
1st vascular tissue
1st stomata
1st megafossils (small club
mosses and other extinct
groups 1st lycopod leave
460
1st evidence of land plants
Sources: Freeman (2002), Purves et al (2001)
A primer on terminology
associated with vascular tissue
Vascular tissue; tissue involved in
transport of materials (water,
minerals…) in plants -- we’re focusing
on water transport in this discussion
Tracheids specialized cells for water
transport; first “true” vascular cells.
Tracheophytes are plants with
Tracheids
Mosses have cells that have a vascular
function, hence its not entirely correct to
refer to them as “nonvascular”, but they
are definitely “non-tracheophyes”, as
are liverworts and hornworts
Tracheophytes have two vascular tissue
types, each composed of several cell
types
Mature vessel elements
in Zea mays; open
tracheids
perforation plate allows
vessel to act as a water
pipe. SEM. Copyright
John N. A. Lott/BPS.
Vessel
elements
xylem; transports water and
dissolved minerals; cell types are
tracheids and, in flowering
plants, vessel elements
phloem; transports sugars, ie,
products of photosynthesis;
minerals too; sieve-tube
members and companion cells
A primer on reproductive cells, embryos, seeds, and
life cycles
Alternation of generations occurs in all plant life cycles,
but not all Charorphyceans; this trait evolved
independently as a derived characteristic of land plants
In some algae with alternation of generations,
sporophytes and gametophytes look similar; not so in
land plants – in all species sporophytes and
gametophytes are very different morphologically
I
Marchantia, a common liverwort. The sporophytes are born within the
tissues of the umbrella shaped structures that arise from the surface
of the flat, green, creeping gametophyte
A primer on reproductive cells, embryos, seeds, and life
cycles
spores are 1n cells that can divide mitotically, with no syngamy,
to produce individuals
gametes are 1n cells that undergo syngamy to produce a (2n)
multicellular individual
embryo embryonic plant that develop from zygotes within
tissues of the female parent (which provides nutrients)
seed Unique structure in “seed plants”; key structure in
domination of terrestrial habitats by plants; plant embryo and its
food supply, packaged in a protective coat. gymosperms
(conifers and their relatives) produce “naked” seeds in that they
are not born in protective chambers. angiosperms produce
seeds
alternation of
generations
Embryo of Marchantia,
a liverwort
Embryo of shepherd’s
purse an angiosperm
Sources: Freeman (2002), Purves et al (2001)
Three ways of expressing (the
same!!) phylogenetic
relationships among major
plant lineages
Cladogram to the left is
particularly useful in that it shows:
-extinct non-seed tracheophyte
lineage Rhyniopsida
-origin of important innovations,
including independent origins -homoplasies
Rhynie in the Grampian
Region of Scotland has
become famous as one of
the most important
palaeobotanical localities
in the world. In 1912 the
Scottish geologist
William Mackie
discovered an occurrence
of Lower Devonian
plant-bearing cherts near
this small village.
Recent radiometric
datings of these rocks
give an age of396 ± 12
million years
Rhynie Chert cut perpendicularly to the
stratification showing successive
horizons
Nature 389, 33 - 39 (1997) © Macmillan Publishers Ltd.
The origin and early evolution of plants on land
PAUL KENRICK AND PETER R. CRANE
the Swedish Museum of Natural History, Box 50007, S-10405, Stockholm, SwedenThe Field Museum,
Roosevelt Road at Lake Shore Drive,
Chicago, Illinois60605, Department of the Geophysical Sciences, University of Chicago, USA.
The origin and early evolution of land plants in the mid-Palaeozoic era, between about 480 and 360 million
years ago, was an important event in the history of life, with far-reaching consequences for the evolution of
terrestrial organisms and global environments. A recent surge of interest, catalysed by palaeobotanical
discoveries and advances in the systematics of living plants, provides a revised perspective on the
evolution of early land plants and suggests new directions for future research.
Our current understanding of Plant
phylogenetic relationships is based on
analysis of both morphological and
molecular characters
•SSU rRNA and Rubisco
•presence/absence of vascular tissue,
leaves, seeds…
The broad picture of plant
macroevolutionary patterns includes…
•Divergenge of entire clade from green algae
•All Plantae lineages; cellulose-based cell
walls, chlorophyll a and b, starch as storage
molecule in chloroplasts
•Two of the three earliest lineages (nontracheophytes) lack water transport cells;
mosses have have limited numbers of them
•Seedless vascular plants (nonseed
tracheophytes) have vascular tissue and
leaves, but reproduce by making spores; no
seeds
Gymnosperms and Angiosperms have
vascular tissue, they have complex leaves,
and they produce seeds.
Rubisco catalyzes a reaction in the CalvinBenson cycle of photosynthesis in which
carbon from CO2 is added to a five-carbon
chain.
Early lineages dependent on wet habitats
and more recent ones not – adaptive
radiations into mesic and xeric conditions
Dense matt of mosses colonizes old lava in
Iceland. Copyright BPS
Leafy liverwort (Lophocolea bidentata),
showing overlapping leaves
andcreeping growth form. Copyright
BPS.
Leafy liverwort (Lophocolea bidentata),
showing overlapping leaves and creeping
growth form. Copyright BPS.
Marchantia, a common liverwort. The
sporophytes are born within the tissues of
the umbrella shaped structures that arise
from the surface of the flat, green,
creeping gametophyte
Hornwort sporophytes. Unlike
other Bryophytes, hornwort
sporophytes are photosynthetic
Gametophytes of Sphagnum moss growing in a bog in central
Newfoundland. Copyright BPS.
Order Lycopodiales:
club moss
(Lycopodium
annotinum); Denali
National Park and
Preserve, AK.
Copyright BPS.
Fern (Blechnum magellanicum)
in rain forest of Chile's
Patagonian coast. Copyright
Alejandro Frid/BPS.
Tree ferns (Dicksonia
antarctica), in a forest of
Eucalyptus regnans;
Australia. Copyright
BPS.
Club Moss Big leaf
maples hung with
epiphytes, most of
which are club
mosses; Hoh Rain
Forest, WA. Copyright
BPS.
Simple determinate
inflorescence of shooting star
(Dodecatheon meadia).
Copyright J. Robert
Stottlemyer/BPS.
Family Arecaceae: desert
fan palm (Washingtonia
filifera); Colorado Desert,
CA. Copyright Jon Mark
Stewart/BPS.
Family Pinaceae: Colorado
blue spruce (Picea
pungens). Copyright
Pollock/BPS.
Family Pinaceae: Pinus
ponderosa, ponderosa pine,
is widespread in the
American West. Copyright
20
First extensive
grassland
The Transition to Land involved evolution of three Sources: Freeman (2002), Purves et al (2001)
important steps
Preventing cell dessication
Transporting water from cells in plant body with direct
access to water, to cells without
Transporting gametes by a mechanism other than
floating or swimming in water
140
First Flowering
Plant
First nectar-drinking
insects
First vessels
Carboniferous
(lycopods, seed ferns,
and horsetails
abundant)
270
360
410
460
fossilized spores in tetrads
1st seeds
1st vascular plant leaves
1st wood
1st roots
1st vascular tissue
1st stomata
1st megafossils (small
club mosses and other
extinct groups and 1st
lycopod leave
First evidence of plants
The earliest interval of plant
evolution on our time scale
has yielded fosils of:
-spores surrounded by tough
membrane made of
sporopollenin
-sheets of a waxy material –
cuticle
-small tubes
Fragment of plant cuticle
Sources: Freeman (2002), Purves et al (2001)
20
140
First extensive
grassland
First Flowering
Plant
Leaf epiderm of dayflower
(Commelina sp.), a monocot. LM.
Copyright Alfred Owczarzak/BPS.
First nectar-drinking
insects
Cross-section of a modern leaf (eudicot)
First vessels
Carboniferous
(lycopods, seed ferns,
and horsetails
abundant)
270
360
410
460
Waxy cuticle solved one problem
and caused another – it impeded
uptake of carbon dioxide
1st seeds
1st vascular plant leaves
1st wood
1st roots
1st vascular tissue
1st stomata
1st megafossils
(small club mosses
and other extinct
groups
1st lycopod leave
modern plants have specialized cells
that solve this problem; two specialized
guard cells form a stoma (pore) that
can be open or closed.
Stomata occur in some extant basal
lineages -- hornworts and mosses
Stomata are known from 385 million
years ago, from a fossil Rhyniopsid
Stomata in leaf of corn, a monocot.
Copyright John N. A. Lott/BPS
20
140
First extensive
grassland
First Flowering
Plant
First nectar-drinking
insects
First vessels
Carboniferous
(lycopods, seed ferns,
and horsetails
abundant)
270
360
410
460
1st seeds
1st vascular plant leaves
1st wood
1st roots
1st vascular tissue
1st stomata
1st megafossils
(small club mosses
and other extinct
groups
1st lycopod leave
Stomata in leaf of corn, a monocot.
Copyright John N. A. Lott/BPS
Sources: Freeman (2002), Purves et al (2001)
Early Devonian rhyniophyte fossils. f. Stomate with
tworeniform guard cells (stippled
Key evolutionary innovations solved the problems
of structural support and internal water transport
First land plants probably were low, sprawling
before evolution of rigid body support, algal-like tissue
could not grow erect, resist gravity
Dense matt of mosses colonizes old lava in
Iceland may be remniscent of early plant life
forms – low and sprawling. Copyright BPS
Before evolution of internal water transport system,
virtually entire plant had to communicate directly with
water
Among communities of low, sprawling plant – growing
horizontally in a sense, competition for space and light
was probably intense –intense selection for erect growth
forms
Transition to terrestrial life required
-internal water transport to high and dry parts of
plant, against the force of gravity
-rigidity of body in order to resist forces of gravity
and wind
Artist’s rendering of Carboniferous forest in a
tropical river delta. Most of the plants
depicted here were nonseed tracheophytes
10 to 20 meters tall. In the distance, earl
seed plants up to 40 meters tall towered over
the forest.
20
140
First extensive
grassland
First Flowering
Plant
First nectar-drinking
insects
Cross section of
vascular bundles from a
eudicot stem; nutrientconducting phloem,
water-conducting xylem.
LM. Copyright James
Solliday/BPS.
Water-conducting xylem
vessels in a cucumber. LM.
Copyright J. Robert
Waaland/BPS.
First vessels
Carboniferous
(lycopods, seed ferns,
and horsetails
abundant)
270
360
410
460
1st seeds
1st vascular plant leaves
1st wood
1st roots
1st vascular tissue
1st stomata
1st megafossils
(small club mosses
and other extinct
groups
1st lycopod leave
Mature vessel elements
in Zea mays; open
perforation plate allows
vessel to act as a water
pipe. SEM. Copyright
John N. A. Lott/BPS.
Modern day tracheids (left) and
vessel elements (right)
Sources: Freeman (2002), Purves et al (2001)
Sources: Freeman (2002), Purves et al (2001)
20
tracheids
First extensive
grassland
Water transport and structural
support
pits
Rhynie chert (~400 mya) bears fossil
plants in an erect, upright postion –
fossils suggest many or most plants
grew erect
140
First Flowering
Plant
Kenrick and Crane identifed four types
of water-conducting cells in the Rhynie
chert (not tracheids or vessel elements)
– some with lignified rings that may
have allowed plants to assume an
upright life form (lignin; strong,
lightweight 6-carbon polymer
vessels
First nectar-drinking
insects
First vessels
Carboniferous
(lycopods, seed ferns,
and horsetails
abundant)
280
360
410
460
top; picture of some of the
first tracheids 380 mya
from the fossil record;
diagram shows tracheids
1st seeds
from modern plant
1st vascular plant leaves
bottom; photo of 50 my old
1st wood
vessels and diagram of
1st roots
modern vessels. Vessels
1st vascular tissue
1st stomata
are shorter and fatter than
1st megafossils
tracheids, and stacked end
(small club mosses
to end. Water flows up
and other extinct
vessels directly, and
groups
laterally, from vessel to
1st lycopod leave
vessl, as well, through
perforations in primary and
above waterconducting
cells from
rhynie chert
By about 380 mya, fossil record bears
tracheids; advanced water conducting
cells found in all modern phyla of
vascular plants. Later tracheids with
extensive lignification and thickened
secondary walls
Wood develops from “secondary
xylem”, and arose independently in
several lineages by about 380 mya.
First trees appear in fossil record some
370 mya
Evolution of heterospory
and male and female
gametophytes
The earliest tracheophytes
were homosporous.
Heterospory evolved multiple
times in tracheophytes in
early evolution of land plants
(occurs in Rhyniophyte
lineage)
Multiple evolutionary origins
suggests heterospory affords
selective advantages;
Later tracheophytes,
especially seed plants, show
ever greater specialiation of
the heterosporous condition
Homosporous plants have a single type of
spore that gives rise to a single type of
gametophyte, which bears two types of sex
organs
Heterosporous plants have two types
of spores, each of which develops into
male or female gametophytes, each of
which produces eggs or sperm
20
First extensive
grassland
Protecting and transporting Embryos: Evolution of seed and pollination
All land plants have life cycles with alternation of generations.
Relationship between gametophyte and sporophyte varies among lineages in terms
of size, dependence, dominance in life cycle
Mosses: sporophyte is small and depends on gametophyte for nutrition
140
First Flowering
Plant
Ferns; sporophyte is larger than gametophyte and is autotrophic
(photosynthesizes its own food)
Seed plants (gymnosperms and angiosperms); sporophyte is dominant;
-male gametophyte is reduced to pollen grain
-female gametophyte to a small structure that holds the egg or eggs
First nectar-drinking
insects
First vessels
Carboniferous
(lycopods, seed ferns,
and horsetails
abundant)
270
360
410
460
1st seeds
1st vascular plant leaves
1st wood
1st roots
1st vascular tissue
1st stomata
1st megafossils (small
club mosses and other
extinct groups and 1st
lycopod leaves
First evidence of
land plants
Gametophytes (green) of the star moss
produce non-photosynthetic stalked
sporophytes with caplike sporangia at their
tips (Campbell 2002)
20
First extensive
grassland
Protecting and transporting Embryos: Evolution of pollen, pollination and seed and seed
dispersal
Seed plants (gymnosperms and angiosperms); sporophyte is dominant;
-male gametophyte is reduced to pollen grain
-female gametophyte to a small structure that holds the egg or eggs
140
First Flowering
Plant
Selection favored male gametophytes highly reduced in size and encased in
sporopollenin; pollen grains are the consequence of that bout of mutation and
selection
Pollen grains survive for prolonged periods in dry environments without
becoming dessicated
Pollen grains can be transported by wind, gravity or animals; through pollen
grains, seed plants lost dependence on water for fertilization
First nectar-drinking
insects
First vessels
Carboniferous
(lycopods, seed ferns,
and horsetails
abundant)
270
360
410
460
1st seeds
1st vascular plant leaves
1st wood
1st roots
1st vascular tissue
1st stomata
1st megafossils (small
club mosses and other
extinct groups and 1st
lycopod leaves
First evidence of
land plants
Pollination. Carrion plant (left) has foul odor that attracts carrion flies.
Hummingbird pollinated flower (middle) produces nectar. Many arge,
complex flowers (eg sunflower, right) attract a host of species that act
as pollinators
20
First extensive
grassland
Evolution of seeds and flowers
Seeds enclose and protects embryo, and has a stockpile of nutrients
Seeds are often attached to a structure that facilitates dispersal by wind, water or
animals
dispersal by wind
140
First Flowering
Plant
First nectar-drinking
insects
First vessels
Carboniferous
(lycopods, seed ferns,
and horsetails
abundant)
270
360
410
460
dispersal by animals
1st seeds
1st vascular plant leaves
1st wood
1st roots
1st vascular tissue
1st stomata
1st megafossils (small
club mosses and other
extinct groups and 1st
lycopod leaves
First evidence of
land plants
dispersal by water
Extra slides
Sources: Freeman (2002), Purves et al (2001)
2
20
First extensive grassland
Overview of the evolutionary history of plants
Consider five intervals of evolutionary history, each defined
by at least one major evolutionary innovation
Archaefructus, an early flower
140
First Flowering Plant
Cones from Araucaria mirabilis, an early gymnsperm
First nectar-drinking insects
Carboniferous
(lycopods, seed ferns,
and horsetails
abundant)
First vessels
Fossil frond of fern (Asterotheca
arborescens); late Carboniferous.
Copyright Barbara J. Miller/BPS.
270
Seed fern leaves
360
410
1st seeds
1st vascular plant leaves
1st wood
1st roots
1st vascular tissue
1st stomata
1st megafossils
(small club
mosses and
other extinct
groups
460
1st lycopod
leave
Fragment of plant cuticle
Fossil stem of oldest known
lycopod genus (Bothrodendron
minutifolium); late Devonian. LM.
Copyright Phil Gates/BPS.
Cells in fossil stem of Rhynia
major (extinct Phylum
Rhyniophyta); late Silurian and
Devonian. LM. Copyright Phil
Gates/BPS.
Spores in fossil Rhynia major; late
Silurian and Devonian. LM.
Copyright Phil Gates/BPS
20
140
First extensive
grassland
First Flowering
Plant
First nectar-drinking
insects
First vessels
Carboniferous
(lycopods, seed ferns,
and horsetails
abundant)
270
360
410
460
1st seeds
1st vascular plant leaves
1st wood
1st roots
1st vascular tissue
1st stomata
1st megafossils (small
club mosses and other
extinct groups and 1st
lycopod leaves
First evidence of
land plants
Key Evolutionary Innovations and Trends in the
Transition of Plants to Land
-reducing water loss; cuticle and stomata
-transporting water; vascular tissue and wood
-transporting gametes and prtoecting embryos;
pollination mechanisms and nutrititive, protective
seeds
Key evolutionary innovations and trends for
capturing energy from sunlight
-Photosynthetic Pathways C3 and C4
-Crassulacean acid metabolism
-growth habits and life forms
Minimizing water loss and regulating gas exchange
Nature 389, 33 - 39 (1997) © Macmillan Publishers Ltd.
The origin and early evolution of plants on land
PAUL KENRICK AND PETER R. CRANE
the Swedish Museum of Natural History, Box 50007, S-10405, Stockholm, SwedenThe Field Museum,
Roosevelt Road at Lake Shore Drive,
Chicago, Illinois60605, Department of the Geophysical Sciences, University of Chicago, USA.
The origin and early evolution of land plants in the mid-Palaeozoic era, between about 480 and 360
million years ago, was an important event in the history of life, with far-reaching consequences for
the evolution of terrestrial organisms and global environments. A recent surge of interest, catalysed
by palaeobotanical discoveries and advances in the systematics of living plants, provides a revised
perspective on the evolution of early land plants and suggests new directions for future research.
Figure 1 Morphological diversity among basal living land plants and potential land-plant sister groups.
a,Coleochaete orbicularis (Charophyceae) gametophyte; magnification × 75 (photograph courtesy of L.
E.Graham). b, Chara (Charophyoceae) gametophyte; magnification × 1.5 (photograph courtesy of M.Feist).
c, Riccia (liverwort) gametophyte showing sporangia (black) embedded in the thallus; magnification× 5
(photograph courtesy of A. N. Drinnan). d, Anthoceros (hornwort) gametophyte showing
nbranchedsporophytes; magnification × 2.5 (photograph courtesy of A. N. Drinnan). e, Mnium (moss)
gametophyteshowing unbranched sporophytes with terminal sporangia (capsule); magnification × 4.5
(photographcourtesy of W. Burger). f, Huperzia (clubmoss) sporophyte with leaves showing sessile yellow
sporangia;magnification × 0.8. g, Dicranopteris (fern) sporophyte showing leaves with circinate
vernation;magnification × 0.08. h, Psilotum (whisk fern) sporophyte with reduced leaves and spherical
synangia(three fused sporangia); magnification × 0.4. i, Equisetum (horsetail) sporophyte with whorled
branches,reduced leaves, and a terminal cone; magnification × 0.4. j, Cycas (seed plant) sporophyte
showing leavesand terminal cone with seeds; magnification × 0.05 (photograph courtesy of W. Burger).
Figure 2 a, Longitudinal section of part of a silicified early fossil gametophyte (Kidstonophyton discoides
from the Rhynie Chert). Antheridia (male sexual organs) are located on the upper surface of the branch;
magnification × 3.4. b, Longitudinal section of antheridium of Lyonophyton rhyniensis from the Rhynie
Chert; magnification × 40. c, Longitudinal section of archegonium (female sexual organ) of Langiophyton
mackiei from the Rhynie Chert; magnification × 80. a–c are from the Remy Collection (slides 200, 90 and
330), Abteilung Paläobotanik, Westfälische Wilhelms-Universität, Münster, Germany (photographs
courtesy of H. Hass and H. Kerp). d, Scanning electron micrograph of Tetrahedraletes medinensis
showing a spore tetrad of possible liverwort affinity from the Late Ordovician (photograph courtesy of W.
A. Taylor); magnification × 670.
Figure 3 Sporophyte diversity in Early Devonian rhyniophyte fossils. a, Cooksonia pertoniiapiculispora:
sporophyte (incomplete proximally) with terminal sporangium15; magnification × 15. b,Tortilicaulis offaeus:
sporophyte (incomplete proximally) with terminal sporangium81; magnification × 40.c. Tortilicaulis offaeus:
sporophyte (incomplete proximally) with terminal bifurcating sporangium81;magnification × 30. d, Transverse
section of sporangium showing thick wall and central spore mass;magnification × 70. e, Details of epidermis at
rim of sporangium; magnification × 45. f, Stomate with tworeniform guard cells (stippled); magnification × 120.
Figure 5 Diversity of water-conducting cells (tracheids) in early land plants (median
longitudinal sectionthrough cells, basal and proximal end wa. lls not shown; cells are 20–40
m diameter). a, Top,bryophyte hydroid; bottom, details of hydroid wall showing distribution of
plasmodesmata-derivedmicropores (10–50 nm diameter; stipple)84. b, Top, S-type tracheid
(fossil) of Rhyniopsida; bottom,details of S-type cell wall showing distribution of
plasmodesmata-derived micropores (stipple) and'spongy' interior to thickenings19. c, Top,
G-type tracheid (fossil) of basal extinct eutracheophytes, whichclosely resemble the
tracheids of some living vascular plants; bottom, details of G-type cell wall showingpores
distributed between thickenings19. d, Top, scalariform pitted P-type tracheid (fossil) typical
oftrimerophyte grade plants (euphyllophytes); bottom, details of P-type cell wall showing pit
chambers andsheet with pores that extends over pit apertures26.