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Kingdom Plantae Plant characteristics (most are shared with Green Algae) • • • • Multicellular eukaryotes Photosynthetic (almost all) Cellulose cell wall Chlorophyll a and b and other photosynthetic pigments – xanthophyll, carotenoids, etc. • Starch is main storage molecule • Unique plant feature – embryos protected by tissues of parent plant - Embryophyta Viridiplantae Streptophyta Plantae Red algae Chlorophytes Charophyceans Embryophytes Ancestral alga Possible Evolutionary Relationships of Plants and Relatives Adaptations to Life on Land Most of the major evolutionary developments we see among plants are the result of adaptations to life on land - the two major challenges to living on land are: • to avoid desiccation or drying out • to support the body Plants have cellulose cell walls which they share with their green algae ancestors - this aids in preventing desiccation; also stiffen the plant to provide some support An outer covering called cuticle, made of a waxy substance called cutin - cuticle is impermeable to water Specialized structures on their leaves (sometimes on stem as well) called stomata which allow plant to breathe in carbon dioxide and breath out oxygen Stomata on underside of a rose leaf Adaptations to Life on Land • The second major trend in dealing with life on land has been the development of a sophisticated vascular system – • A system of vessels or ducts (known as xylem) running through plants allows them to conduct water from roots to leaves and stems; • A complementary system (known as phloem) also moves sugars and carbohydrates from leaves (where sugars are produced by photosynthesis) to rest of plant Adaptations to Life on Land • Plants grow from particular parts of the plant body known as apical meristems – these are localized regions of the root tip and shoot tip where cells actively divide and grow Apical meristem of shoot Developing leaves Apical meristems of plant shoots and roots. The light micrographs are longitudinal sections at the tips of a shoot and root. Apical meristem of root Shoot 100 µm Root Apical Meristems 100 µm Adaptations to Life on Land • Land plants have developed multicellular embryos that are nutritionally dependent upon an adult plant to grow – because they possess this multicellular embryo, the land plants are often referred to as Embryophytes Pea Seed - Embryo Alternation of Generations • Plants exhibit a phenomena known as alternation of generations - this phenomena is shared with some green algae as well • Plants alternate between a diploid generation - the sporophyte; and a haploid generation - the gametophyte • The names refer to the reproductive structures produced by each generation • Plant evolution has tended to place more emphasis on sporophyte over time Nonvascular Plants are United By: • A general lack of specialized vascular tissues • Sporophytes of mosses, liverworts and hornworts are almost always smaller than gametophytes, and get food from the gametophyte • All nonvascular plants have motile sperm which must swim through water to reach the eggs • They lack cuticle and stomata Liverwort – Division Hepatophyta Liverwort – Division Hepatophyta • 9000 species • gametophytes either lie flat on ground and grow at one end or some have leaves, stems and rhizoids (fleshy structures for attachment to ground) like mosses • sporophyte usually attached to gametophyte, sporophyte usually unstalked and spherical Hornwort – Division Anthocerophyta Hornwort – Division Anthocerophyta • 100 species • usually have fleshy gametophytes • sporophytes are long and horn-shaped, stand up from surface of flat gametophytes Moss – Division Bryophyta Moss – Division Bryophyta • 15,000 species • gametophytes are almost always leafy with small simple leaves; the plant itself may be tufted or creeping • sporophyte are usually yellow or brown at maturity and have sporangium at their tip - they are borne individually on gametophytes • when moss spores germinate they give rise to filaments of cells called protonema that look like green algae - the leafy gametophytes grow up from buds on the protonema • Many mosses are very important economically Sphagnum Bogs - Canada Sphagnum Peat cutting today - Scotland Cooksonia – 408 MYA – early vascular plant Vascular Plant Features • • • • • • Efficient and sophisticated vascular systems Large dominant sporophytes Specialized leaves, stems and roots Development of heterosporous plants Advanced cuticle and stomata Eventual evolution of seeds Vascular Elements of Vascular Plants • Xylem – tissue that transports water and mineral nutrients from roots to rest of plant – made up of hard- walled cells called tracheary elements • Phloem – tissue that transports sugars and carbohydrates from areas where they are made by photosynthesis to all other parts of the plant – made up of soft-walled cells called sieve elements Growth in Vascular Plants • Primary growth – growth due to cell division at tips of stems and roots – at apical meristems • Secondary growth – growth due to cell division in periphery of plant – growth at lateral meristems Plant Secondary Growth Note Vascular Cambium is the Lateral Meristem Division Pterophyta - Ferns Division Pterophyta - Ferns • 12,000 species – largest group of seedless vascular plants • found throughout the world, but most abundant in the tropics • range from aquatic ferns less than 1 cm in diameter to tree ferns up to 24 m tall • sporophyte is most conspicuous part of fern life cycle • have motile sperm, must be in areas with abundant water or moisture to reproduce • structure of most sporophytes is to have a stem that runs along the ground or in the soil called a rhizome; from the rhizome roots extend into soil; leaves stick up into air and are called fronds; sporangia are found on leaves – usually in clusters called sori Structure of a Fern Polypodium sori Division Psilophyta - Psilotum – Whisk Fern Division Psilophyta - Psilotum – Whisk Fern • only 2 genera, very few species – all tropical • no true leaves; vascular structure is the same throughout the plant axis – no differentiation • gametophytes occur in the soil; produce antheridia and archegonia • motile sperm Division Sphenophyta Equisetum hyemale Division Sphenophyta - Horsetails • 15 species • characterized by jointed stems and leaves in whorls around the stem at each joint • some fossils are tree-sized but all living species are 1 m or less in height • found in most of the world • motile sperm Division Lycophyta Club Mosses Division Lycophyta - Club Mosses • 1200 living species; many extinct species including fossils of 30 m tall trees • club mosses (Lycopodium) • spike mosses (Selanginella) • produce male and female gametophytes • motile sperm Evolutionary trends in the seed plants • The ovule becomes modified into a seed – a fertilized embryo with a food supply and protective covering or seed coat • Continued emphasis on the sporophyte generation with the gametophyte becoming nutritionally dependent upon the sporophyte Development of a Gymnosperm Seed Seed plants diverged into two groups • Gymnosperms - naked seeds - seed (ovule) not covered at time of pollination - after pollination, ovule becomes covered to form seed - so the pollination is direct • Angiosperms - vessel seeds - ovule enclosed by sporophyte tissue (the carpel) at time of pollination - so pollination occurs by growth of pollen tube carrying sperm to ovule pollination is indirect Division Cycadophyta – Sago-Palms Division Cycadophyta – Sago-Palms • 130 living species; many more extinct common in age of dinosaurs • distinct trunk covered with bases of shed leaves • functional leaves at top of stem in a cluster • pollen and seed cones on separate plants (male and female plants) • have motile sperm Divison Gingkophyta Gingko biloba Division Gingkophyta - Gingko • 1 living species; many more extinct • little changed in 80 million years • characterized by fan-shaped leaves with branching veins • separate male and female trees • have motile sperm Division Gnetophyta Ephedra – Mormon Tea Welwitschia Division Gnetophyta • 3 very different genera; 75 species • very unusual group • many angiosperm like features such as strobili similar to flowers, very similar xylem tissue • immobile sperm • Ephedra (Mormon tea) is a shrub, Welwitschia is a bizarre desert plant, Gnetum is genus of tropical vines and trees Division Coniferophyta – Conifers Division Coniferophyta – Conifers • pines, firs, spruces, junipers, cypresses, hemlocks, redwoods • 600 species • have leaves (needles) which resist desiccation adapted to life in dry or extreme habitats • most species are evergreen - don't shed leaves • immobile sperm - fertilization via pollen tube • dominant plants of many ecosystems • major source of lumber and pulp products Division Magnoliophyta – Flowering Plants Division Magnoliophyta– Flowering Plants • 275,000 species (at least) • have flowers • double fertilization in ovary, produces embryo and endosperm (unique to angiosperms) • oldest fossils from 130 MYA, group is probably 150 MY old; first came to dominate about 80 MYA; modern familes of plants appear about 65 MYA magnolias, beeches, beans • immobile sperm Flower structure Amborella trichopoda • Oldest group of flowering plants is represented by just one species – Amborella trichopoda – found only in New Caledonia. Has long tracheid cells in the xylem but lacks shorter, fatter vessels typical of more recent angiosperms. Amborella flowers The Water Lilies • The water lilies are another ancient lineage with ancient features such as complex flowers with many repeated units of parts – lots of petals, stamens, etc. In flowering plant evolution we see a reduction in flower part number. The two main groups of Magnoliophyta • Class Dicotyledones or Magnoliopsida - dicots most flowering trees, mints, beans, sunflowers, roses, etc. – the Eudicots • 190,000 species • 2 cotyledons in the embryo • leaves with netlike web of veins • flower parts usually in multiples of 4 or 5 • Class Monocotyledones or Liliopsida - monocots grasses, sedges, lillies, orchids, onions, irises derived from dicots by reducing number of cotyledons • 85,000 species • one cotyledon in embryo often retain endosperm • leaves with parallel veins • flower parts usually in multiples of 3 Rosa californica – typical dicot Columbia Lily – typical monocot Success of Flowering Plants due to: • Flowers that promote efficient transfer of gametes • Development of fruits (mainly the covering of the seeds) and many ways to disperse fruits • Tough leaves with efficient cuticle and stomata and advanced vascular systems allowed them to develop and spread during a relatively dry period in earth history • Chemicals which discourage herbivory