Plant Evolution
What are plants?
MulticellularEukaryoticPhotosynthetic autotrophsCell Walls made of cellulose
Plant Ancestors
Plants are the descendants of protistsPlants are most closely related to charophycean algae, a type of green algae
Unique Plant Characteristics (not shared with Carophyceans)
Apical Meristems—localized regions of cell division at the tips of shoots (stems) & rootsMuticellular plant embryosAlternation of GenerationsWalled spores produced in sporangiaMulticellular Gametangia (archegonia & antheridia)
Alternation of Generations—The Plant Life cycle
Life on Land and Conserving Water
Leaves and other plant parts are covered with water repellant cuticle (made of lipids!)Stomata support photosynthesis and regulate transpirationXylem tissue for transporting water from roots to leavesPhloem tissue for transporting sugars from leaves to stems and roots
Plant Groups
Bryophytes (mosses)—first descendants of Charophyceans & first land plantsPteridophytes (ferns)—descendants of bryophytes; first plants with vascular tissueGymnosperms (“naked seed”)—descendant of pteridophytes; first plants with seedAngiosperms (enclosed seed)—descendants of gymnosperms; first plants with flowers
Bryophytes
Bryophytes
Do not have vascular tissue Tend to be short and must live close to waterSperm have to swim to the egg; requires a water medium
The Origin of Vascular Plants
Contain Xylem and PhloemHave a dominant sporophyte generationPteridophytes (seedless vascular plants) are oldest vascular plants
The Origin of Seed Plants
Reproductive Adaptations:Continued reduction of the gametophyte The advent of the seedThe evolution of pollen
Spores Vs. Seeds
Single Celled
Haploid
Multicellular & More ComplexDiploidSporophyte EmbryoFood SupplyProtective Coat
Formation of Seed
Seed develops from the megasporangiumThe megasporangium is encased with layers of integuments for protectionThe megaspore becomes one or more eggsThe integument, megasporangium, and megaspore are the ovule
Pollen
Microspores develop into pollen grainsPollen grains mature into the male gametophyteIn mosses & ferns the sperm is flagellated and must swim to the eggIn gymnosperms & angiosperms, the sperm travels via the wind and then through a pollen tube to the egg
Gymnosperm & Angiosperm differences
Gymnosperms (naked seed) lack the enclosed chambers (ovaries) in which angiosperm ovules & seeds developGymnosperm ovules & seed develop on surfaces of specialized leaves called sporophyllsGymnosperms are much older than angiosperms
Angiosperms
Produce flowers & fruitSeed is encased in the fruitAll belong to phylum AnthophytaAngiosperm xylem has fiber cells which specialize for supportVessel elements in xylem are more efficient in transporting water
The Flower—The Angiosperm Invention
The Fruit—To Aid Seed Dispersal
Fruit = Mature ovaryFruits protect seed & aid in dispersalCan act as kites or propellers; can have burrs that cling; or can be delicious to eat