Chapter 29: Overview of Plant Diversity Divya Raj, Katie Redinger, Allie Wrabel

The Evolutionary Origins of Plants Plant will refer to a group of organisms that share a freshwater algal ancestor and have evolved over a 470-million-year period The exact ancentral alga is still a mystery, but close relatives like the Charales exist today The shared history green algae has with other plants has led scientists to change the name of kingdom Plante to kingdom Viridiplante to include the algae

Land Plants All afford protection to their embryos All have multicellular haploid and diploid phases

Conductive Systems Nonvascular Plants- lack vascular tissue Vascular Plants- have water-conduction xylem and food-conducting phloem strands of tissues in their stems, roots, and leaves.

Four Major Groups of Land Plants Nonvascular plants- not monophyletic, include three phyla: mosses, liverworts, and hornworts Seedless vascular plants- (1) club mosses, and (2) ferns, whisk ferns, and horsetails. Gymnosperms- have seeds that protect their embryos Angiosperms- have flowers, which may attract pollinators, and fruits surrounding the seeds, protecting the embryos and aiding in seed dispersal

Adaptations to Land Many plants are protected from desiccation-the tendency of organisms to lose water to the air-by a cuticle that is secreted onto their exposed surfaces Gas diffusion into and out of the plant occurs though tiny openings called stomata Evolution of leaves increases the amount of photosynthetic surface area

Plant Life Cycles Humans have diplontic life cycles, while plants have haplodiplontic Diploid sporophytes produce haploid spores by meiosis Spores develop into haploid gametophytes by mitosis and produce haploid gametes

Haploid Diploid Gametophyte (n) Mitosis Spore Sperm Egg n n n Spores n Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Haploid Gametophyte (n) Mitosis Spore Sperm Egg n n n Spores n Meiosis Gamete fusion Spore mother cell 2n Zygote 2n 2n Embryo Sporangia Sporophyte (2n) Diploid

Mosses, Liverworts, and Hornworts Nonvascular plants are divided into three major phyla-Bryophyta, Hepaticophyta, and Anthocerophyta- with all members being relatively unspecialized but collectively able to inhabit diverse environments

Mosses The leaf like structures belong to the gametophyte. Each of the yellowish brown stalks with a capsule at is summit is a sporophyte

Liverworts The sporophytes are formed by fertilization within the tissues of the umbrella-shaped structures that arise from the surface of the flat green, creeping, gametophyte

Hornworts Unlike the sporophytes of other bryophytes, most hornworts sporophytes are photosynthetic

Seedless Vascular Plants Seedless vascular plants have well-developed conducting tissues in their sporophytes.

The first vascular plants for which we have a relatively complete record of belonged to the phylum Rhyniophya. They flourished some 410 million years ago but are now extinct. These plants were homosporous (only produce one type of spore for reproduction; asexual). Seeds only occur in heterosporous plants (two types of spores for reproduction; sexual). Eventually these ancient vascular plants evolved more complex arrangements, leading to the formation of real leaves.

Early plants soon began to develop vascular tissues that acted as efficient water and food conducting systems. These consist of strands of specialized cylindrical or elongated cells that form a network throughout a plant, extending from near the tips of the roots, through the stems, and into true leaves.

The seven living phyla of vascular plants dominate terrestrial habitats everywhere, except for the highest of mountains and the tundra. Most vascular plants have well-developed conducting tissues, specialized stems, leaves, roots, cuticles, and stomata. Many have seeds, which protect embryos until conditions are suitable for further development.

Earliest vascular plants lacked seeds. Two phyla of seedless vascular plants: Lycophyta  Club mosses (relicts of an ancient past when vascular plants first evolved.) Pterophyta  Whisk ferns, Horsetails, and Ferns. All reproduce using sporophytes (asexually).

In modern vascular plants, the gametophytes have been reduced in size and complexity, individuals have specialized tissues. Gametophytes are the phases where gametes are produced for sexual reproduction (two parts).

Archegonium Mitosis Rhizoids Egg Gametophyte Spore Sperm n MEIOSIS Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Archegonium Mitosis Antheridium Rhizoids Egg Gametophyte Spore Sperm n MEIOSIS FERTILIZATION Mature sporangium 2n Mature frond Embryo Leaf of young sporophyte Sorus (cluster of sporangia) Adult sporophyte Rhizome Gametophyte

Seed Plants First appeared 425 million years ago Descended from spore-bearing plants called progymnosperms This common ancestor gave way to gymnosperms and angiosperms

Formation Embryo is protected by extra tissue, creating an ovule Tissue hardens to form seed coat This protects the embryo from drought and helps disperse the seed Presence of seeds introduced dormant phase- allows embryo to survive until conditions are better

Reproduction 2 kinds of gametophytes- male and female In seed plants, the sperm moves to the egg through a pollen tube eliminating the need for external water Unlike seedless plants, whole male gametophyte moves to female Female gametophyte develops in ovule

Gymnosperms- “naked-seeded plants” Cone-bearing seed plants; ovules not completely enclosed at time of pollination 4 groups: conifers, cycads, gnetophytes, and Ginkgo Can range from 25g to 45 kg and mm’s to over a m

Conifers Ex. Pines, spruces, firs, cedars, hemlocks, yews, larches, cypresses, and others Found in colder temperate and drier regions Sources of timber, paper, resin, taxol, and other products

Pines Over 100 species exist Tough, needlelike leaves produced in clusters of 2 to 5 Thick cuticle and recessed stomata- adaptation for preventing water loss Secrete resin used in turpentine and rosin Wood consists of xylem and is considered ‘soft’

Reproduction- Males Seed plants are heterosporus so spores give rise to two types of gametophytes Male gametophytes develop from microspores A pair of microsporangia form sacs in which numerous ‘mother’ cells undergo meiosis creating 4 microspores Develop into 4-celed pollen grains with air sacs Single cluster of male pine cones can produce over 1 million pollen grains

Reproduction- Female Two ovules develop near base and contain megasporangium called nucellus Nucellus is surrounded by cells called the integument with small opening called the micropyle Single megaspore mother within each megasporangium undergoes meiosis and becomes 4 megapsores Only one survives and develops into female gametophyte and can contain thousands of cells

Pollination Pollen is drawn into microphyle While female is developing, pollen makes its way through nucellus One of the pollen’s 4 cells divide through mitosis and one of these two divides again Final cells are sperm 15 months after pollinations, zygote is formed

Ovulate (seed-bearing) cone Sporophyte Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Mature seed cone (2nd year) Pollen tube Megaspore Mitosis Pollination Pollen FERTILIZATION (15 months after pollination) n Mitosis Mitosis Embryo Microspores Longisection of seed, showing embryo Microspore mother cell MEIOSIS 2n Pine seed Pollen-bearing cone Scale Mitosis Megaspore mother cell Seedling Scale Ovulate (seed-bearing) cone Sporophyte

Cycads (Cycadophyta) Slow-growing in tropical and subtropical regions Life cycle similar to pines Sperm is formed within pollen tube and released within ovule to archegonium Sperm cells are largest among living organisms

Gnetophytes (Gnetophyta) 3 genera, 65 species Only gymnosperms with vessels in xylem Over half are in genus Ephedra and plants are shrubby and have scalelike leaves Species of genus Gnetum are vineline with broad leaves

Ginkgo (Ginkgophyta) Only one living species remains Name comes from fan-shaped leaves Sperm have flagella and ginkgo is dioecious- male and female reproductive structure produced on different trees Resistant to air pollution

Angiosperms- “Vessel seed” Flowering plants; ovules completely enclosed in tissue 250,000 known species Vessel in name refers to carpal- modified leaf that encapsulates seeds

Origins Fossils as old as 125 million years old Known to be angiosperms because fossils have both male and female reproductive structures Lack petals and sepals that evolved later

Monocots and Eudicots Eudicots (175,000)- more primitive; 1/6 of species are annuals; mints, peas, sundlowers Monocots (65,000)- lilies, cattails, orchids; few are annual; have no ‘true’ wood

Structure of flowers Stamen Anther Megaspore Stigma mother cell Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Structure of flowers Stamen Stigma Anther Megaspore mother cell Filament Style Nucellus Carpel Petal Ovule Sepal Integuments Ovary Receptacle Micropyle Stalk of Ovule (funiculus) Pedicel

(microgametophytes) (n) (megagametophyte) (n) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Life Cycle Generative cell Microspore mother cells (2n) Sperm MEIOSIS Tube nucleus Anther (2n) Mitosis Tube nucleus Microspores (n) Pollen grains (microgametophytes) (n) Stigma Megaspore mother cell (2n) Pollen tube Anther Megaspore (n) MEIOSIS Mitosis Egg Style Ovary Ovule Adult sporophyte with flower (2n) 8-nucleate embryo sac (megagametophyte) (n) 2n n DOUBLE FERTILIZATION Formation of pollen tube (n) Embryo (2n) Seed coat Polar nuclei Germination Cotyledons Young sporophyte (2n) Egg Seed (2n) Sperm Endosperm (3n)