Origin of Land Plants (Embryophytes)
Origin of Land Plants (Embryophytes)
Origin of Land Plants (Embryophytes)
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<strong>Origin</strong> <strong>of</strong> <strong>Land</strong> <strong>Plants</strong> (<strong>Embryophytes</strong>)<br />
Why?<br />
Ancestors=Green algae=Chlorophyta<br />
Chlorophyll a & b-used in photosynthesis<br />
Carotenoids & xanthophylls-accessory pigments<br />
Starch (stored carbohydrate) in chloroplasts<br />
Cellulose cell walls<br />
Oogamy<br />
Phragmoplast<br />
Cell plate<br />
Alternation <strong>of</strong> generations life cycle – sporophyte &<br />
gametophyte<br />
Green algae very diverse unicells, colonies<br />
spherical balls <strong>of</strong> cells, coencytic filaments, 2D &<br />
3D branched forms,
Which group <strong>of</strong> green algae is the<br />
closest to land plant origins?<br />
Class: Charophyceae<br />
Order: Coleochaetales<br />
Family: Coleochaetaceae<br />
Genus: Coleochaete<br />
cell plate<br />
phragmoplast<br />
plasmodesmata (multicellular growth)<br />
lignin-like compounds (found in secondary wall<br />
thickenings in vascular plants)<br />
sporopollenin (found in pollen & spores <strong>of</strong> vascular<br />
plants)<br />
suberin-like compounds (found in casparian strip <strong>of</strong><br />
endodermis in vascular plants and in bark (phellem)
Cooksonia<br />
Upper Silurian –earliest vascular plant
Cooksonia sprg<br />
Dianne Edwards, UK<br />
Cooksonia tracheid
Tetrads <strong>of</strong> four spores<br />
Products <strong>of</strong> meiosis
Brochotriletes<br />
Sporae<br />
Dispersae<br />
Genera<br />
From<br />
Rhynie<br />
Chert<br />
Apiculiretusispora<br />
Emphanisporites<br />
Dictyotriletes
Upper Silurian landscape-Cooksonia
Dawson 1859<br />
Described early land plants from the Lower<br />
Devonian <strong>of</strong> New Brunswick and Quebec-<br />
Gaspé Bay-compression/impressions<br />
Dichotomizing axes, some with spine-like<br />
projections, sprg<br />
Ignored until 1917 Kidston and Lang started<br />
to publish on the plants from the Rhynie<br />
Chert
Rhynia gwynne-vaughanii<br />
Vascular plants in the<br />
Rhynie Chert
Rhynia gwynne-vaughanii
Rhynia gwynne-vaughanii<br />
Stomatal apparatus<br />
Ridged cuticle surface<br />
Epidermal cells
Rhynia gwynne-vaughanii<br />
Tracheids with annular secondary wall thickenings<br />
Sporangium with abscission zone
Rhynia<br />
gwynne-vaughanii<br />
Sporangia
Rhynia gwynne-vaughanii<br />
Growth habit<br />
Rhizoids on hemispherical projections<br />
New reconstruction<br />
Sporangia shed<br />
Plant branches below sprg
Rhynie Chert landscape reconstruction
Vascular plants described by<br />
Kidston and Lang<br />
1. Rhynia gwynne-vaughanii<br />
2. *(=Rhynia major) now Aglaophyton major<br />
3. Asteroxylon mackiei<br />
(note part <strong>of</strong> this plant is now Nothia)<br />
4. *Hornea lignieri now Horneophyton lignieri<br />
now<br />
5. *Nothia aphylla El Sadadawy & Lacey 1979<br />
(Lyon 1964 recognized problem)<br />
6. Trichopherophyton teuchansii Lyon &<br />
Edwards 1991<br />
7. Ventarura lyonii Powell et al. 2000
Aglaophyton major x.s.<br />
Now not considered to be a vascular plant
Asteroxylon mackiei<br />
Now considered to be a lycopod – a vascular plant
Horneophyton lignieri<br />
Now not considered to be a vascular plant
What Dawson found<br />
• Axes with terminal sporangia<br />
• Some spiny<br />
• Some with smooth surfaces<br />
• Several types
Early land plants<br />
Classification by Harlan Banks, 1968<br />
Division: Tracheophyta<br />
Subdivision: Rhyniophytina<br />
Subdivision: Zosterophyllophytina<br />
Subdivision: Trimerophytina<br />
Subdivision: Psilotophytina<br />
Psilotum and Tmesipteris
Harlan Banks
Subdivision: Rhyniophytina<br />
• Oldest known vascular plants – U. Silurian<br />
• E.g., Cooksonia, Rhynia<br />
• No roots<br />
• No leaves<br />
• Naked axes (green and photosynthetic)<br />
• Dichotomous branching<br />
• Terminal sprg<br />
• Simple, slender protosteles, centrarch<br />
maturation <strong>of</strong> primary xylem<br />
• Small plants – less than 1 m tall - @20 cm
Rhynia gwynne-vaughanii<br />
Growth habit<br />
Rhizoids on hemispherical projections<br />
New reconstruction<br />
Sporangia shed<br />
Plant branches below sprg
Tom Taylor & David Edwards<br />
Fossil fungi & Rhynia reconstructions
<strong>Plants</strong> that used to be in<br />
Rhyniophytina but have been<br />
removed<br />
• Aglaophyton major ( = Rhynia major<br />
Kidston & Lang)<br />
• Horneophyton lignieri Kidston & Lang<br />
• Nothia aphylla El-Saadawy & Lacey<br />
(Lyon 1964 did not provide a diagnosis)<br />
Unfortunately, now not classified<br />
anywhere – called “rhyniophytoid” in<br />
lab manual
Sawdonia
Sawdonia
Zosterophyllum<br />
myretonianum
Subdivision: Zosterophyllophytina<br />
• L. Devonian (or U. Silurian?)<br />
• E.g., Zosterophyllum, Sawdonia, Gosslingia,<br />
Rebuchia (see sheets)<br />
• No leaves<br />
• No roots<br />
• Some naked axes, some with enations<br />
• Dichotomous branching<br />
• Sprg are cauline (on side <strong>of</strong> stem)<br />
• Protosteles circular or elliptical- exarch<br />
• A little more robust than rhyniophytes,<br />
maybe up to 1 m tall<br />
• Sterile and fertile zones on plant<br />
• Evolved from rhyniophytes?- gave rise to<br />
lycopods
Psilophyton crenulatum Doran
Trimerophytina<br />
Trimerophyton<br />
Psilophyton
Subdivision: Trimerophytina<br />
• Middle & Upper Devonian<br />
• E.g., Trimerophyton, Psilophyton, Pertica<br />
• No leaves<br />
• No roots<br />
• Naked axes or enations<br />
• Branching more variable than other grps.<br />
– Dichotomous, trichotomous<br />
• Growth habits- monopodial, pseuomonopodial<br />
• Terminal sprg in pairs<br />
• Sterile & fertile zones<br />
• Protosteles -slender, centrarch<br />
• Larger plants than rhyniophytes<br />
• Thought to have evolved from rhyniophytes and given<br />
rise to the other groups <strong>of</strong> vascular plants
Subdivision: Psilotophytina<br />
• Psilotum<br />
• Tmesipteris<br />
• Extant plants with protosteles<br />
• Enations<br />
• Dichotomous branching<br />
• Green photosynthetic stems<br />
• Synangia (Psilotum 3 sprg, Tmesipteris 2)<br />
• No leaves, no roots<br />
• No fossil record
Aglaophyton<br />
major<br />
(=Rhynia<br />
major)<br />
px=protoxylem, 1 st formed<br />
mx=metaxylem,<br />
formed 2 nd
sporangia
Stomata & rhizoids
Aglaophyton major<br />
reconstruction
Rhyniophytoid plants or<br />
Protracheophytes<br />
Used to be in Rhyniophytina but on<br />
reexamination they have been removed-<br />
Due to studies by Kenrick and Crane 1991<br />
on the conducting cells <strong>of</strong> early land plants<br />
Subsequent work by Friedman & Cook 2000 &<br />
others<br />
3 types<br />
1. No secondary wall thickenings<br />
2. G-type<br />
3. S-type
Discovery <strong>of</strong> Rhynie Chert<br />
gametophytes<br />
Changed our ideas about early land<br />
plants<br />
Remy & Remy 1980’s onward-believed<br />
Three types <strong>of</strong> gametophytes found, now<br />
several more are known<br />
Both permineralized and<br />
compression/impression gametophytes<br />
now known
Aglaophyton conducting cells<br />
No secondary wall thickenings<br />
Like the hydroids & leptoids<br />
<strong>of</strong> mosses<br />
Bubble-like<br />
structures in<br />
some cells-<br />
Probably<br />
taphonomic
Aglaophyton<br />
major<br />
(=Rhynia<br />
major)<br />
Px = hydroids<br />
Mx = leptoids
Lyonophyton – gametophyte <strong>of</strong> Aglaophyton
Lyonophyton antheridium with sperm
Lyonophyton –<br />
gametophyte <strong>of</strong> Aglaophyton
Horneophyton
Horneophyton rhizoids
Horneophyton<br />
Plant base & rhizoids
Horneophyton sporangia & spores
Horneophyton sprg<br />
with columella &<br />
spores
Anthoceros<br />
A hornwort<br />
(bryophyte)<br />
sporophyte<br />
gametophyte<br />
Sporangium (capsule) has a columella
Horneophyton stoma and conducting cells<br />
Tracheids? Debatable
Langiophyton – gametophyte <strong>of</strong> Horneophyton
Langiophyton with archegonia
Langiophyton<br />
Gametophyte<br />
<strong>of</strong><br />
Horneophyton
Nothia aphylla<br />
A dichotomy<br />
Short and giant cells in epidermis
Nothia rhizoids
Nothia sporangia
Nothia<br />
reconstructions
Nothia reconstruction
Kidstonophyton – gametophyte <strong>of</strong> Nothia
Kidstonophyton<br />
Gametophyte <strong>of</strong><br />
Nothia
How Rhynie Chert gametophytes<br />
assigned to sporophytes<br />
• Epidermal cell morphology<br />
• Conducting cell type<br />
• Stomatal organization<br />
• Presence <strong>of</strong> glands (sunken, Horneophyton)
Compression/<br />
impression<br />
gametophytes<br />
from the<br />
Devonian<br />
Sciadophyton<br />
Calyculiphyton
S-type tracheid<br />
G-type tracheid<br />
S=Sennicaulis<br />
e.g. Rhynia<br />
G=Gosslingia<br />
e.g. Psilophyton<br />
Kenrick & Crane<br />
1991
Rhynie Chert landscape reconstruction
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