Plant Diversity I How Plants Colonized Land Chapter 29

Plants vs. Algae Land plants evolved from Charophytes (Chara) green algae 4 key traits plants share with Charophytes (Morphological and Biochemical Evidence): 1. Rose-shaped complexes for cellulose synthesis 2. Peroxisome enzymes 3. Structure of flagellated sperm 4. Formation of a phragmoplast

5 key traits in nearly all land plants but are absent in the charophytes: 1. apical meristems 2. multicellular dependent embryos 3. alternation of generations 4. walled spores produced in sporangia 5. multicellular gametangia females – archegonia & males – antheridia

Fig. 29-5e Apical meristem of shoot Developing leaves Apical meristems Apical meristem of root Root 100 µm Shoot

Fig. 29-5b Embryo Maternal tissue Wall ingrowths Placental transfer cell (outlined in blue) Embryo (LM) and placental transfer cell (TEM) of Marchantia (a liverwort) 2 µm 10 µm

Fig. 29-5a Gametophyte (n) Gamete from another plant n n Mitosis Gamete FERTILIZATIONMEIOSIS Mitosis Spore n n 2n2n Zygote Mitosis Sporophyte (2n) Alternation of generations

Fig. 29-5c Spores Sporangium Sporophyte Longitudinal section of Sphagnum sporangium (LM) Gametophyte Sporophytes and sporangia of Sphagnum (a moss)

Fig. 29-5d Female gametophyte Male gametophyte Antheridium with sperm Archegonium with egg Archegonia and antheridia of Marchantia (a liverwort)

Fig Origin of land plants (about 475 mya) Origin of vascular plants (about 420 mya) Origin of extant seed plants (about 305 mya) ANCES- TRAL GREEN ALGA Liverworts Hornworts Mosses Lycophytes (club mosses, spike mosses, quillworts) Pterophytes (ferns, horsetails, whisk ferns) Gymnosperms Angiosperms Seed plants Seedless vascular plants Nonvascular plants (bryophytes) Land plants Vascular plants Millions of years ago (mya)

Characteristics of all land plants: eukaryotic, multicellular, autotrophic cell walls made mostly of cellulose chlorophylls a & b Domain Eukarya, Kingdom Plantae In many plants, additional terrestrial adaptations, such as vascular tissues and secondary compounds, also evolved.

Nonvascular plants 1. Represented by three phyla: a. phylum Hepatophyta – liverworts b. phylum Anthocerophyta – hornworts c. phylum Bryophyta - mosses Liverworts Hornworts Moss

Fig. 29-9a Thallus Gametophore of female gametophyte Marchantia polymorpha, a “thalloid” liverwort Marchantia sporophyte (LM) Sporophyte Foot Seta Capsule (sporangium) 500 µm

gametophyte - mass of green, branched, one-cell-thick filaments sporophytes are smaller; only present part of the time spores germinate in favorable habitats sporophyte gametophyte sporophyte gametophyte 2.The gametophyte is the dominant generation in the life cycle

Fig The life cycle of a moss. Key Haploid (n) Diploid (2n) Protonemata (n) “Bud” Male gametophyte (n) Female gametophyte (n) Gametophore Rhizoid Spores Spore dispersal Peristome Sporangium MEIOSIS Seta Capsule (sporangium) Foot Mature sporophytes Capsule with peristome (SEM) Female gametophytes 2 mm Raindrop Sperm Antheridia Egg Archegonia FERTILIZATION (within archegonium) Zygote (2n) Embryo Archegonium Young sporophyte (2n)

3. Bryophyte sporophytes disperse enormous numbers of spores sporophytes remain attached to gametophyte throughout the lifetime –depends on the gametophyte for sugars, amino acids, minerals and water. sporangium (site of meiosis and spore production) can generate over 50 million spores.

4. Bryophytes provide many ecological and economic benefits distributed worldwide common and diverse in moist forests and wetlands Some common in extreme environments (mountaintops, tundra, and deserts)

Sphagnum, a wetland moss, is especially abundant and widespread. forms extensive deposits of undecayed organic material, called peat Wet regions dominated by Sphagnum or peat moss are known as peat bogs

Fig (a) Peat being harvested (b) “Tollund Man,” a bog mummy

Bog People

THE ORIGIN OF VASCULAR PLANTS 1. Two conducting tissues of the vascular system A. Xylem – Dead tissue, water-conducting B. Phloem – Living tissue, food-transporting 2. Water-conducting cells are strengthened by lignin and provide structural support 3. Sporophyte generation is dominant in vascular plants.

Seedless vascular plants 4. Two modern phyla: a. phylum Lycophyta – club mosses b. phylum Pterophyta - ferns, whisk ferns, and horsetails Club moss Horsetail Whisk fern Fern

Fig a Lycophytes (Phylum Lycophyta) Selaginella apoda, a spike moss Isoetes gunnii, a quillwort Strobili (clusters of sporophylls) 2.5 cm Diphasiastrum tristachyum, a club moss 1 cm

Fig e Pterophytes (Phylum Pterophyta) Athyrium filix-femina, lady fern Vegetative stem Strobilus on fertile stem 1.5 cm 25 cm 2.5 cm Psilotum nudum, a whisk fern Equisetum arvense, field horsetail

5. Most seedless vascular plants are homosporous, producing one type of spore that develops into a bisexual gametophyte both archegonia (female sex organs) and antheridia (male sex organs) Eg., ferns sporophyte Single type of spore Bisexual gametophyte eggs sperm

Fig The life cycle of a fern. Key Haploid (n) Diploid (2n) MEIOSIS Spore dispersal Sporangium Mature sporophyte (2n) Sorus Fiddlehead Spore (n) Young gametophyte Mature gametophyte (n) Archegonium Egg Antheridium Sperm FERTILIZATION New sporophyte Gametophyte Zygote (2n)

6. seedless vascular plants are most common in damp habitats 7. ferns produce clusters of sporangia, called sori, on the back of leaves

Seedless vascular plants formed vast “coal forests” during the Carboniferous period These plants left not only living representatives and fossils, but also fossil fuel in the form of coal.