Phylogeny & Diversity of Plants Prokaryotes - organisms without any membrane-bound organelles In time, prokaryotes started to evolve How did the naked DNA become enclosed? = infolding of the plasma membrane Part of the infoldings detach and become the endoplasmic reticulum 4.6B years ago - the origin of the earth 3.5B years ago - the first evidence that life started to exist on earth (only bacteria for 1.7B years), oceans were inhabited by scavengers (heterotrophic, anaerobic bacteria) 2.3B years ago - oxygen became permanent in the atmosphere, started the great oxygenation event (heralded the beginning of many things, e.g. first mass extinction on earth) Engulfing smaller aerobic heterotrophic prokaryotes = mitochondrion Organism with mitochondrion engulfing a cyanobacterium = will become a plastid THREE DOMAINS OF LIFE - All organisms we know on earth today are descended from a common ancestor that lived about 4 billion years ago - Domain BACTERIA, ARCHAEA, EUKARYA 3. Archaeplastida a. E.g. red algae, chlorophytes, charophytes, land plants 4. Unikonta a. E.g. molds, fungi, amoebas, all animals ARCHAEPLASTIDA LUCA We can say that bacteria were the original organisms on earth but at some point there came to be archaeans which are primitive prokaryotes and from the archaean branch came the eukaryans If all organisms with chlorophyll a are included - chlorobionta If only the chlorophytes and all true plants - viridiplantae If only include those who are very close to plants - streptophyta All embryophytes - plantae Charophytes below are not forming embryos. land plants, in general, are embryophytes, which are mostly related to the charophytes, which are the most advanced of the green algae Charophytes and embryophytes are sister taxa, both descended most likely descended from chlorophytes SUPERGROUPS 1. Excavata a. E.g. euglena 2. SAR clade a. E.g. diatoms, golden algae, dinoflagellates Phylogeny of Plants Origin of land plants from Charophycean algae EVIDENCES: Similarity in: - Pigments (chlorophylls a and b, carotenes, xanthophylls) - Cellulosic cell-wall components - Starch as carbohydrate storage material - Presence of plasmodesmata Red algae - closest to chlorophytes Chlorophytes - closest to charophytes Charophytes - closest ancestor to true plants (land plants) There are true plants that are located in water so there are certain exceptions. All vascular plants - tracheophytes Plants with true leaves - euphyllophytes Producing seeds - gymnosperms and angiosperms Derived traits of Plants Five key traits appear in nearly all land plants but are absent in charophytes a. alternation of generations b. Multicellular, dependent embryos c. Walled spores produced in sporangia d. Multicellular gametangia e. Apical meristems The Land plants (embryophytes) - - = embryophyta The first colonization of plants on land during the Silurian period, ca. 400 million years ago Land plants now dominate earth Sporophyte body -> mitosis, growth, and differentiation -> sporocyte -> meiosis -> spores -> mitosis, growth, and differentiation -> gametophyte body -> mitosis, growth, and differentiation -> if (antheridium - sperm) if (archegonium egg) -> fertilizaition -> mitosis, growth, and differentiation -> embryo -> mitosis, growth, and differentiation -> sporophyte body Sporophyte: - Allowed for many propagules (spores) produced - Sporophyte (diploid) shields against deleterious recessives Multicellular Gametangium - Among the charophytes below every single part of the gametangium will become a gamete - In the case of true plants - there is always a sterile jacket of cells - Antheridium - there can be so many sperm cells that could be contained and the entire antheridium is protected by a sterile jacket of cells - Oogonium - Only 1 egg cell per oogonium (archegonium) Apical meristem - where growth occurs TEN PHYLA OF LIVING PLANTS Bryophytes Bryophytes’ major characteristics - Similarity with green algae: chlorophyll a&b, starch, cellulosic cell walls, motile sperms - Non-vascular - Lack true leaves, stems, and toots, yet true plants - Get nutrients from dust, rainwater, and substances dissolved in water at soil’s surface via diffusion/osmosis - With heteromorphic life cycle dominated by gametophyte - With heteromorphic alternation of generation - Monoecious or dioecious - Dominant, photosynthetic gametophyte (roots, stems, leaves not homologous to the vascular plants) - Dependent sporophyte (foot, seta, capsule protected by calyptra) Where are they found? - Somewhere with moisture Bryophyte diversity (3 divisions) DIVISION I: Bryophyta (Mosses) - 1200 species - Spphagnidae (peat mosses: 200 Sphagnum s pp.) - About 1% of the terrestrial surface covered by Sphagnum - Andreaeidae (lantern mosses) - Bryidae (95% of moss species) DIVISION II: Hepatophyta (Liverworts) DIVISION III: Anthocerophyta (Hornworts) - Cave moss: true moss I. - Bryophyta - the true mosses Lack vascular tissues - Some moss species with water-conducting cells (hydroids) and sugar-conducting cells (=leptoids) but not as specialized as in the vascular plants II. - Hepatophyta Liverworts - 8000 species worldwide - 2 orders (Marchantiales: “Thalloid”; Jungermanniales: “Leafy:) Sporophyte, gametophyte tallus Liverworts, growth forms, asexual reproduction, gemmae cups, spore dispersal, elaters, peristome teeth Antheridiophore, gametophyte thallus archegoniophore, III. - Anthocerophyta - The Hornworts Thalloid body Single large chloroplast cell Sporophyte - Long and narrow - Splits lengthwise - Indeterminate growth - Rhizomatous Dichotomously branched Rootless THE HORNWORT Anthoceros Advance features of Vascular Plants (=Tracheophytes) 1. Sporophyte-dominant life cycle Evolution and Diversity of Land Plants 1. Non-vascular plants 2. The seedless vascular plants 3. The seed plants Highlights of plant evolution Origin of Vascular Plants and (=Tracheophytes) - The first tracheophytes were in the now-extinct phylum Rhyniophyta - Cooksonia - Evolved over 400 million years ago - Oldest known vascular plant - Sporophytic axis branched with multiple sporangia 2. The tracheophytes have well-developed vasculature, consisting of a. Xylem conducts water and minerals from the soil to the aerial parts of the plants, or from one place in the soil to another i. Xylem consists of ray cells and lignin-stiffened tracheids, vessels, fibers - Lignin hard substance secreted within secondary cell wall - Secondary cell walls are found in tracheids, vessels, fibers (all dead cells) - The evolution of tracheids had two important consequences: - Provided a pathway for long-distance transport enabling vascular plants to grow much larger - Provide rigid structural support b. Phloem conducts photosynthetic products from production sites to sites where they are used or store (think ‘source-sink’) i. Consists of sieve elements, fibers, parenchyma 1. Sieve cells only sieve areas (all vasc. Plants except angiosperms) 2. Sieve tube members with sieve plates found only in angiosperms Evolution of vascular cylinder (=stele) in plants 3. Evolution of roots form subterranean portions of stems 4. Evolution of leaves: a. Microphylls are small leaves with a single, unbranched vein b. Megaphylls are typically larger and have a branched system Evolution of Leaves i. ii. iii. In heterosporous plants, the megaspore develops into a larger, specifically female gametophyte (megagametophyte) The microspore develops into the smaller, male gametophyte (microgametophyte) Heterospory evolved independently and repeatedly, suggesting that it affords selective advantages Homosporous spore production 5. Heterospory a. plants that bear a single type of spore are said to be homosporous i. The most ancient tracheophytes were all homosporous ii. A single type of gametophyte bears both female and male reproductive organs b. Plants with two distinct types of spores evolved later, and are said to be heterosporous 6. Reduction in size of gametophytes with corresponding increase in size of sporophytes 7. Development of seeds a. Gymnosperms and angiosperms 8. Development of flowers and fruits a. Angiosperms Consensus phylogeny, lycophytes, spermatophytes, molinophytes, euphyllophytes EVOLUTION PLANTS OF SEEDLESS VASCULAR Lycopodiophyta - lycophytes Apomorphies: 1. Roots dichopodial apical meristem may branch into two 2. Root protoxylem endarch (to inside) a. Protoxylem - first xylem formed b. Metaxylem - later xylem 3. Stem protoxylem exarch (to outside) 4. Sporangia compactly form strobilus 5. Microphyllous Selaginellaceae - Spike-moss family - 1 genus: Selaginella (700 spp.) Centrarch, endarch, exarch, mesarch CLASS LYCOPODIOPSIDA FAMILY Lycopodiaceae 5 genera: Lycopodium, Phylloglossum - Huperzia, Lycopodiella, Pseudolycopodiella, All homosporous ISOETOPSIDA Selaginellaceae + Isoetaceae 1. Leaves ligulate 2. Heterosporous - 2 types of spores LIFE CYCLE: Selaginella Tracheophyta - Classification Equisetopsida (Equisetophytes) Equisetaceae Equisetum Horsetails Scouring rushes Phylum Monilophyta: Ferns, Horsetails, and Whisk ferns and relatives a. Ferns are the most widespread seedless vascular plants, with more than 12000 species b. They are most diverse in the tropics but also thrive in temperate forests c. Horsetails were diverse during the Carboniferous period, but are now restricted to the genus Equisetum d. Whisk ferns resemble ancestral vascular plants but are closely related to modern ferns / Apormorphies: 1. Stem ribbed with canals 2. Leaves reduced, whorled 3. Sporangiophore 4. Spores with elaters, chlorophyllous, gametophyte Horsetail spores with chlorophyllous gametophyte elaters, Psilotum nudum (whisk fern) The Whisk ferns - Include two genera of rootless, spore-bearing plants, Psilotum and Tmesipteris - Psilotum has only minute scales instead of true leaves - Although whisk ferns resemble the most ancient tracheophytes, they are now considered to be highly specialized plants that evolved fairly recently - Homosporous, spores contained in fused sporangia called synagium - Gametophyte subterranean saprophytic Sori arrangements in ferns - Marginal Gametophyte of nudum lives underground Ferns - Sporophytes of the ferns typically have true roots, stems, and leaves. - Ferns are characterized by fronds, large leaves with complex vasculature - Sporangia are found on the undersurfaces of the fronds, clustered in groups called sori - Some ferns undergo circinnate vernation to protect the young fronds - Gametophyte (prothallus), epiterranean, photosynthetic - Terrestrial ferns all homosporous - Aquatic ferns (Azolla, Salvinia, marsilea) all heterosporous, spores in sporocarps ‘ - Extramarginal Costal Intercostal - Acrostichoid Polypodiaceae - Sori exindusiate (no indusium “naked”) - Indusiate - with indusium Sorus (pl. sori) - aggregation of sporangia Indusium - flap Prothallus Common apomorphies gymnosperms and angiosperms among The Seed Plants 1. WOOD a. Results from secondary growth b. Secondary growth results from cell division in the lateral or secondary meristems called VASCULAR CAMBIUM and CORK CAMBIUM c. Vascular cambium produces secondary xylem = wood (from greek word xylos) “Wood” = secondary xylem, or everything on the interior side of the vascular cambium “Bark” = everything exterior of the vascular cambium, including the secondary phloem and the periderm (cork cambium + cork) Secondary growth happens in roots too Seed vs spore - Seed: a reproductive body consisting of a young, multicellular plant and food reserves, enclosed by a seed coat - Spore: a single ell with minimal food reserves to sustain the plant that develops from a germinating spore - Seeds are reproductively superior to spore Pinaceae - Pollen cones with 2 microsporangia/microsporophyll - Pollen grains of some taxa saccate (with 2 bladders) Adaptive significance of seeds 1. Protection of embryo (seed coat) 2. Nutrition of embryo (nutritive tissue = female gametophyte in gymnosperms) 3. Dispersal unit (e.g. fleshy, carried by animals; winged, transported by wind) 4. Dormancy mechanisms (seed coat involved in preventing germination except when conditions right) Gymnosperms - Seeds usually 2 per ovuliferous scale, inverted, winged - Leaves linear to acicular (needle-shaped) In some taxa, short shoots (e.g. Cedrus) or determinate fascicles (Pinus) II. Angiosperms Angiosperms - Flowering plants = Magnoliophyta Major characteristics/apomorphies: 1. Flowers (generally with perianth) 2. Stamens with 2 lateral thecae 3. 3-nucleate male gametophyte 4. Carpel and fruit 5. Ovules with two integuments 6. Reduced female gametophyte 7. Endosperm and double fertilization 8. Sieve tube members and companion cells Angiosperms - the currently most advanced and successful plant group - - May be parasitic, saprophytic, epiphytic, carnivorous, or completely photosynthetic Include herbs, shrubs, vines, lianas, trees Include annual, biennial, perennial plants Co-evolution with Animals: key to angiosperm evolutionary success - Pollination of flowers by animals - Transport of seeds by animals - Are two important relationships in terrestrial ecosystems Fruits can be carried by wind, water, or animals to new locations, enhancing seed dispersal How are angiosperms currently grouped? Emphasis on Group Relatedness! How do we know angiosperm relationships? - Cladistic analyses: parsimony, maximum likelihood, Bayesian - Use of all types of data: morphological, anatomical, embryological, palynological, karyological, chemical, and molecular data - Most useful: multiple gene sequence data Monocotyledons (Monocotyledonae, Monocots) - Monophyletic group - Comprises 22% of all angiosperms - Relationships to other “basal” angiosperms unclear at present Apomorphies of the Monocots 1. Sieve tube plastids with cuneate (wedge-shaped) proteinaceous inclusions 2. Atactostele stem vasculature 3. Parallel leaf venation 4. Single cotyledon NOTE: a trimerous flower merosity is not a monocot - - Most Speciose Angiosperm Taxa - Sunflower family (ASTERACEAE) - 24000 species - Orchid family (ORCHIDACEAE) - 20000 species - Legume or pea family(FABACEAE) - 18000 species - Total form these three families = 62000 species, roughly 24% of all flowering plant species on earth - Flowering plant species = 260000 Top ten angiosperm families with the most number of genera Products from flowering plants Humans depend on flowering plants for food Just 6 crops - wheat, rice, maize (corn), potatoes, cassava (manioc), sweet potatoes - yield 80% of all the calories consumed by humans Also for wood medicines, clothing, paper, fiber, dye, etc… HOW MANY ARE USED FOR MEDICINE - 75% of the world population depends on traditional herbal medicine - 25% of our common medicine contain some compounds from plants
