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