Homosporous and Heterosporous Plants Green Algae and Land Plants Homosporous: produce a single type of spore that develops into a bisexual gametophyte that produces both gametes Homosporous and Heterosporous Plants Evolution of Pollen • when pollen evolved, heterosporous plants lost their dependence on water for fertilization • pollen grains • tiny enough to be carried by wind or animals Heterosporous: the production of two distinct types of spore-producing structures and two distinct types of spores, male and female Seeds • allow embryos to be dispersed to a new habitat, away from the parent plant Seed Plants -gymnosperms and angiosperms • are often dispersed by wind, water, or animals • the evolution of heterospory, pollen, and seeds triggered a dramatic radiation of seed plants (about 290 mya) - production of seeds and pollen grains - embryo develops within seed coat Heterospory in Gymnosperms ME IOS PO L Microspore (n) forms pollen grain Cones with microsporangia Pollen grains disperse via wind MITOSIS IS Pollen grain (male gametophyte LIN AT IO N Four meiotic products; one is large and forms the megaspore (n) Megasporangium ME IOS Ovulate cone Ovules (contain megasporangia) Female gametophyte (n) Eggs (n) ION ILIZAT FERT MITOSIS Pollen produces sperm Mature sporophyte (2n) Developing sporophyte Pollen grain Mother cell (2n) Archegonia Embryo (2n) Three meiotic products die IS Megaspore divides to form female gametophyte (n), which produces archegonia and eggs by mitosis. (Only one egg is fertilized and develops.) Note that the red dots here and elsewhere represent nuclei Seed (disperses via wind or animals) Flowering plants - Angiosperms Flowers ~250,000 spp. • Flowers contain two key reproductive structures: stamens and carpels • The stamen contains the anther: microsporangia • The carpel contains the ovary in which the ovules are found: megasporangia • The evolution of the flower is an elaboration of heterospory, with the key innovation being the evolution of the ovary success of angiosperms in terms of geographical distribution, number of individuals, and number of species revolves around a reproductive organ: the flower Heterospory in Angiosperms MITOSIS Microspore (n) forms pollen grain Carpel Ovule Ovary MITOSIS MEIOSIS Egg Female gametophyte (n: retained in ovary) Nutritive tissue Endosperm (3n) forms nutritive tissue in seed FE R Mature sporophyte flower (2n) TIL IZ Megasporangium Megaspore (n: retained in ovary) N Anther Stamen Flower Pollen grains disperse via wind or animals (the red dots here Pollen lands and elsewhere are nuclei) near female gametophyte; produces PO pollen tube and LL Pollen grain sperm IN AT (male gametophyte) IO N Sperm travel down growing pollen tube to reach egg AT IO MEIOS IS Flowers Embryo (2n) MITOSIS Developing sporophyte Seed (disperses via wind or animals) Zygote (2n) Flowers: • vary in size, structure, scent, and color in order to attract different pollinators • evolution of the flower made efficient pollination possible Fruits The Angiosperm Radiation Fruit: • a structure that is derived from the ovary and encloses one or more seeds • evolution of fruit made efficient seed dispersal possible • Angiosperms represent one of the great adaptive radiations in the history of life • The diversification of angiosperms is associated with three key adaptations: (1) vessel elements, (2) flowers (modified leaves), and (3) fruits • These adaptations allow angiosperms to transport water, pollen, and seeds efficiently Innovations That Allow Plants to Reproduce Efficiently on Land Land plants Vascular plants Seed plants C yc ad s G in kg R o ed w G oo ne ds to e Pi ph t a l. ne yt e s A e s s ng t a io l. sp er m Ly co ph yt W es hi sk H or fern se s t Fe ail s rn s Li ve rw o H or rts nw or M os ts se s R U ed al ga e lv op C hy s ole te oc s ha et St e on ew or ts Gymnosperms Key Lineages of Green Plants Fruit Flowers Heterospory Seeds Pollen Heterospory Sporophyte-dominated life cycle Green algae Nonvascular plants Seedless vascular plants Alternation of generations Retention of embryo on parent Complex gametangia Thick-walled spores Retention of egg on parent Simple gametangia Green Algae Ulvophyceae Green algae es e tes aet rts ga hy ch wo l a p o e n ed vo le o R Ul Co St Land plants - unicellular and multicellular - freshwater and marine -important primary producers in aquatic habitats - alternation of generation in multicellular species Two groups most similar to land plants Bryophytes: Non-Vascular Plants Land plants Coleochaetophyceae - most grow as flat sheets of cells (attached to water lilies, cattails) - strictly fresh water algae - multicellular -no alternation of generation - only zygote is diploid Non-vascular plants Green algae ts ts or or s rw rnw sse e v o o Li H M Charaphyceae (Stoneworts) -strictly fresh water - multicellular -no alternation of generation - only zygote is diploid Nonvascular Plants Hepaticophyta: Liverworts • most basal lineages of land plants • 3 lineages with living representatives: liverworts, hornworts, and mosses Anthocerophyta: Hornworts • stomata* • rhizoids • cuticle* • pores* • rhizoids Bryophyta: Mosses • simple water conducting tissues* • rhizoids The Seedless Vascular Plants Land plants Lycophyta: Lycophytes or Club Mosses Seedless vascular plants es ns s yt fer ail ph sk set ns o c hi or r Ly W H Fe - most ancient plants with roots * - tree-sized lycophytes (dominated the coal-forming forests of the Carboniferous period) Psilotophyta: Whisk Ferns • no fossil record • lack roots • rhizomes * Pteridophyta: Ferns Sphenophyta (or Equisetophyta): Horsetails - Horsetail stems are hollow, allowing oxygen to diffuse down their hollow stems to roots Seed Plants Land plants • only seedless vascular plants to have large, welldeveloped leaves (fronds)* Seed plants Gymnosperms . al s et s s yte al. erm d p o ph e t s o s o io ad gk w to s yc in d e ne ng C G Re Gn Pi A Gymnosperms Cycadophyta (Cycads) • “naked seed” • no flowers • lack motile cells – pollen* • tracheids* (lack vessel elements found in angiosperms) • woody* • compound leaves (unique) • many are treesized • symbiotic, nitrogen-fixing cyanobacteria Ginkgophyta (Ginkgoes) Cycas revoluta Gnetophyta (Gnetophytes) - diverse form • 1 species is fossil living day - drug ephedrine has been isolated from this group alive today • deciduous* Pinophyta (pines, spruce, firs) • named for its reproductive structure, the cone • needle-like leaves* Other Conifers (redwoods, junipers, yews) • all trees and shrubs • narrow or scale-like leaves • wind-pollinated Anthophyta (Angiosperms) • flower: defining adaptation of angiosperms • supply the food that supports virtually every species