Chapter 20
Three important clades of green algae are the chlorophytes, coleochaetophytes, and stoneworts
The chlorophytes are the sister group of all the other green plants
The closest relatives of vascular plants lacked roots:
The closest relatives of living vascular plants belonged to several extinct groups called rhyniophytes
Petals
brightly colored and attract pollinators * many flowers have specialized sterile (non-spore-bearing) leaves, the inner ones are petals
corolla
collection of petals
monoecious
having male and female reproductive organs in the same plant or animal
Cotyledons are
seed leaves
Key Adaptation permitted plants to colonize land
•Trend toward reduction of the gametophyte generation in plant evolution. •In seed plants, the gametophyte develops partly or entirely while attached to, and nutritionally dependent, on the sporophyte.
"Ground Pine" and selaginella
•True roots •Have leaflike structures (microphylls) •Sporangia in clusters called strobili
The gametophyte produces haploid gametes by mitosis.
•What does the fusion of gametes produce? - zygote •What structure develops into the sporophyte? - embryo
The diploid zygote develops by mitosis and cytokinesis into a multicellular embryo, which eventually grows into a mature diploid plant.
•What is the name of the multicellular, diploid stage? - Sporophyte
Hornworts
* 100 species and named because their sporophytes often look like horns * cells of hornworts each contain a single large, platelike chloroplast, whereas the cells of the other two groups contain numerous small lens-shaped chloroplasts. *sporophytes in all three groups, those of the hornworts come closest to being capable of growth without a set limit
Survival on land was facilitated by the evolution among plants of numerous adaptations, including:
- The cuticle, a coating of waxy lipids that retards water loss - stomata, small closable openings in leaves and stems that are used to regulate gas exchange and water loss - gametangia, multicellular organs that enclose plant gametes and prevent them from drying out - embryos, young plants contained within a protective structure - certain pigments that afford protection against the mutagenic ultraviolent radiation that bathes the terrestrial environment - thick spore walls containing a polymer that protects the spores from desiccation and resists decay - a mutually beneficial association with fungi (mycorrhizae) that promotes nutrient uptake from the soil
A vascular system:
1.Xylem: moves water 1.Lignin in the cell walls 2.Phloem: moves sap
double fertilization
A fertilization process that requires two sperm to fuse with two other cells
Ovary
A flower structure that encloses and protects ovules and seeds as they develop.
aggregate fruit
A fruit such as a raspberry that develops from a single flower that has several carpels.
Rhyniophytes
A group of early vascular plants that appeared in the Silurian and became extinct in the Devonian. Possessed dichotomously branching stems with terminal sporangia but no true leaves or roots.
Conifers
A gymnosperm, or naked seed plant, that produces cones (cone bearing plants)
endosperm
A nutrient-rich tissue formed by the union of a sperm cell with two polar nuclei during double fertilization, which provides nourishment to the developing embryo in angiosperm seeds.
The seed is a complex, well-protected package:
A seed contains tissues from three generations. A seed coat develops from the the integument - the tissues of the diploid sporophyte parent that surround the megasporangium
megaspore
A spore from a heterosporous plant species that develops into a female gametophyte. *megasporemetophyte that produces only eggs
heterosporous
A term referring to a plant species that has two kinds of spores: microspores that develop into male gametophytes and megaspores that develop into female gametophytes. *Most vascular plants are heterosporous: •The sporophyte must develop two types of sporangia
Features of the seed plant life cycle protect gametes and embryos:
A trend in plant evolution: the sporophyte became less dependent on the gametophyte, which became smaller in relation to the sporophyte * This trend continued with the seed plants, whose gametophyte generation is reduced even further than it is in the ferns
pollen tube
A tube that forms after germination of the pollen grain and that functions in the delivery of sperm to the ovule.
Life cycles of land plants feature alternation of generations:
A universal feature of the life cycles of land plants is alternation of generations * The life cycle includes both a multicellular diploid stage and a multicellular haploid stage * Gametes are produced by mitosis, not by meiosis. Meiosis produces spores that develop into multicellular haploid organisms
Rhizomes
Anchored in the soil by horizontal portions of stem
Embryophytes
Another name for land plants, recognizing that land plants share the common derived trait of multicellular, dependent embryos.
After fertilization, the ovary of a flower (together with the seeds it contains) develops into a fruit that protects the seeds and can promote see dispersal
As we will see both flowers and fruits afford major reproductive advantages to angiosperms
sporangia
Cells contained with specialized reproductive organs of the sporophyte
Flower structure has evolved over time: The flowers of the earliest-diverging clades of angiosperms have a large and variable number of tepals (undifferentiated sepals and petals), carpels and stamens
Change within the angiosperms has included some striking modifications of this early condition: reductions in the number of each type of floral organ to a fixed number, differentiation of petals from sepals, and changes in symmetry from radial ( as in a lily or magnolia) to bilateral (as in a sweet pea or orchid), which often accompanied by extensive fusion of parts
Double fertilization:
Each pollen grain contains two sperm nuclei: one combines with egg to form diploid zygote. The other combines with two other haploid nuclei of the female gametophyte to form a triploid cell that forms the endosperm, The endosperm nourishes the embryo during its early development.
Magnoliids
Early branching angiosperms groups include the water lilies, star anise and its relatives and the magnoliids. The magnoliids include many familiar and useful plants, such as avocados, cinnamon, black pepper, and magnolias
The first carpels to evolve were leaves wit marginal sporangia, folded but incompletely closed
Early in angiosperm evolution, the carpels fused with one another, forming a single, multichambered ovary
The sexual structures of angiosperms are flowers: Flowers come in astonishing variety of forms
Flower may be single, or they may be grouped together to form an inflorescence *A group of flowers tightly clustered together.
Most angiosperms are pollinated by animals, and they have coevolved.
Flowers often provide food for pollinators (nectar and pollen) and have specialized structures or colors to attract them.
Reconstruction of an Ancient Forest:
Forests of the carboniferous were characterized by abundant vascular plants such as club mosses, fern, and horsetails, some of which reached heights of 40 meters. These forests were the source of modern coal deposits.
Fruits aid angiosperm see dispersal:
Fruits typically aid in seed dispersal. Fruits may attach or be be eaten by an animal. The animal is then likely to move, after which the seeds may fall off or be defecated
Cycads
Gymnosperms that grow in tropical or subtropical areas; look like palm trees with cones
filament
Holds up the anther
Equisetum
Horsetail (equisetum) is only living genus in equisetaceae (horsetail family), a family of vascular plants that reproduce by spores rather than seeds.
Stamens or the carpels are nonfunctional or absent in a given flower, and the flower is referred to as
Imperfect
microstrobilus
In conifers, male pollen-bearing cone.
megastrobilus
In conifers, the female (seed-bearing) cone.
The angiosperm life cycle produces diploid zygotes nourished by triploid endosperms:
In most angiosperms, the other sperm nucleus combines with two other haploid nuclei of the female gametophyte to form a cell with triploid (3n) nucleus
archegonium
In plants, the female gametangium, a moist chamber in which gametes develop.
Sepals
Leaflike parts that cover and protect the flower bud
green plants
Like land plants, the green algae contain both chlorophylls a and b and store their reserve of photosynthetic products as starch in chloroplasts. ** All groups that share these features are commonly called green plants because both of their photosynthetic pigments are green
Gnetophytes
Live in hot deserts and tropical rain forests; can be a tree, vine, or shrub * a long-lived desert plant with just two permanent straplike leaves, which split into many pieces that sprawl across the sand
nonvascular land plants
Liverworts, mosses and hornworts lack tracheids * do not form a clade unlike the vascular plants, which are clade
Cones
Male and female cones contain the reproductive structures of conifers •Large female cone, seeds exposed on the upper surfaces of the scales. •Small male pollen cone Wind transports pollen grains (male gametophyte) from the male cone to the female cone. Pollen tube delivers the sperm nucleus to the egg. •Some conifers (e.g., juniper and yew) have modified cones; soft, berry-like tissue surrounds the seeds.
Seed plants: Angiosperms and Gymnosperms •They are heterosporous. Microsporangium > microspores > male gametophyte that is shed: the pollen grain.
Megasporangium > megaspores > female gametophyte that remains within the megasporangia. Female gametophytes are dependent and protected by the sporophyte
two largest angiosperm groups:
Monocots (1 cotyledon) include grasses, cattails, lilies, orchids, and palmsEudicots (2 cotyledons) include the vast majority of familiar seed plants
Pollen, Seed, and Wood contributed to the success of seed plants:
New innovation appeared when some plants developed extensively thicken woody stems. The two other innovations, pollen and seeds, arose in the seed plants. ** Pollen increases reproductive opportunities in a terrestrial environment, and seeds provide a secure and lasting structure that protects the dormant stage of the embryo
Generalized flowers that has functional megasporangia and microsporangia and microsporangia are referred to as
Perfect ( or hermaphroditic)
overtopping
Plant growth pattern in which one branch differentiates from and grows beyond the others. *Overtopping would have given these plants an advantage in the competition for light, enabling them to shade their dichotomously branching competitors
Algae
Plantlike protists *Most aquatic photosynthetic eukaryotes (other than those secondarily derived from land plants)
A perfect flower represents a compromise of sorts: Attracting a pollinating bird or insect, the plant is attending to both male and female functions with a single flower type
Plants with imperfect flowers must create the attraction twice - once for each flower type
Hermaphroditic
Possessing both the male and the female reproductive organs
The perfect flower is self pollination, which is usually disadvantageous
Potential problem is that female and male functions might interfere with each other - stigma might be placed where it makes it difficult for pollinators to reach the anthers - which reduces the pollen to other flower
Spores
Produced by meiosis. Grow into haploid organisms by mitosis.
Recent analysis have revealed the phylogenetic relationships of angiosperms:
Shows the relationships among the major angiosperms clades
Ferns appeared in the Devonian period
Sporangia in clusters called sori. •Microphylls were probably the first leaflike structures to evolve
Vascular plants (tracheophytes)— have vascular bundles Nonvascular plants—some have conduction cells, but no vascular bundles
Stomata: not present in liverworts
Several distinct clades of algae were among the first photosynthetic eukaryotes
The ancestor of Pantae was unicellular and may have been similar in general form to the modern glaucophytes
A change in stem anatomy enabled seed plants to grow to great heights
The earliest fossil seed plants have been found in late Devonian rocks. These plants had extensively thickened woody stems, which developed through the proliferation of xylem
Pistil
The female reproductive part of a flower
Conifers have cones and lack swimming sperm
The great Douglas fir and cedar forests found in the northwestern US and he massive boreal forests of pine, fir and spruce of the northern regions of Eurasia and North America, as well as on upper slopes of mountain ranges elsewhere, rank among the greatest forests of the world
Horsetails and ferns constitute a clade
The horsetails and ferns were once thought to be only distantly related. As a result of genomic analysis, we now know that they form a clade: the monilophytes
Diversification of vascular plants made land more suitable for animals
The initial absence of herbivores (plant-eating animals) on land helped make the first vascular plants successful *By the late Silurian (about 425 mya), the proliferation of land plants made the terrestrial environment more hospitable to animal * Arthropods, vertebrates, and other animals moved onto land only after vascular plants became established there.
Nonvascular land plants live where water is readily available
The living species of nonvascular land plants are the liverworts, mosses and hornworts * These three groups are thought to be similar in many ways to the earliest land plants *Most of these plants grow in dense mats, usually in moist habitats
integumentary
The megasporangium is surrounded by sterile sporophytic structures, which form an integument that protects the megasporangium and its contents
Vascular plants branched out: several feature that were new to the vascular plants evolved in lycophytes and monilophytes
The monilophytes and seed plants constitute a clade call the eduphyllophytes
Flowers and Fruits Led to Increased Diversification of Angiosperms:
The most obvious feature defining the angiosperms is the flower, which is their sexual structure * Productions of fruits is also a shared derived trait of angiosperms
The zygote develops into an embryo with one or two cotyledons (seed leaves).
The ovule develops into a seed that encloses the diploid embryo and the triploid endosperm.
micropyle
The pollen grain enters through a small opening in the integument at the tip of the ovule, the micropyle
Stamens
The pollen-producing male reproductive organ of a flower, consisting of an anther and filament.
microphylls
The small leaves of lycophytes that have only a single, unbranched vein, which are arranged spirally on the stem
Heterospory appeared among the vascular plants
The spores produced by the sporophyte are a single type and develop into a single type of gametophyte that bears both female and male reproductive organs. Such plants, which bear a single type of spore are called homosporous
gametophyte
The stage in the life cycle of a plant in which the plant produces gametes, or sex cells.
Style
The stalk of a flower's carpel, with the ovary at the base and the stigma at the top.
Pollination
The transfer of pollen from male reproductive structures to female reproductive structures in plants Pollination— transfer of pollen grain (=male gametophyte) to the female gametophyte •A pollen tube required to bring the sperm nucleus to the egg so fertilization can occur. •The diploid zygote divides to form an embryo • •Gymnosperms and angiosperms no longer require water for getting the sperm to the egg, allowing them to colonize drier habitats.
Gymnosperms have naked seeds:
The two major groups of living seed plants are the gymnosperms (such as pines and cycads) and the angiosperms (flowering plants) Gymnosperms—seed plants that do not form flowers or fruits •Ovules and seeds not protected by ovary (fruit) tissue
Liverworts
There are about 9,000 species * most have green, leaflike gametophytes that lie close to or flat on the ground •Green, leaf-like gametophytes •Sporophyte remains attached to the gametophyte •Asexual and sexual reproduction
The overtopping growth of the euphyllophytes also allowed a new type of leaflike structure to evolve
This larger, more complex leaf is called megaphyll * Megaphylls—more complex leaf; may have arisen from flattening of a branch tip.
secondary growth
This type of growth, which increases the diameter of stems and roots in some modern seed plants is called secondary growth, and its products is called secondary xylem or wood
Angiosperms have coevolved with animals:
Whereas most gymnosperms are pollinated by wind, most angiosperms are pollinated by animals * The many different mutualistic pollination relationships between plants and animals are vital to both parties * Many flowers entice animals to visit them by providing food rewards. Pollen grains themselves sometimes serve as food for animals
Vascular tissues led to rapid diversification of land plants
Xylem - conducts water and minerals from the soil to aerial parts of the plant.
Rhizoids
bore water-absorbing unicellular filaments *These plants also bore aerial branches and sporangia homologous to the sporangia of mosses - were found at the tips of those branches
Phloem
conducts products of photosynthesis from production sites to use or storage sites.
strobili
cone-like structures that contain the sporangia, which are clusters of spore-bearing microphylls attached to the end of the stem
multiple fruits
develop from a group of flowers called an inflorescence
embryo
developing stage of a multicellular organism, which eventually grows into a mature diploid plant
simple fruit
develops from a single carpel of one flower, or several fused carpels, such as a plum or peach
dichotomous
divided or dividing into two parts or classifications *the apex (tip) of the shoot divided to produce two equivalent new branches, with each pair of branches diverging at approximately the same angle from the original stem
ovule
female reproductive structure of a seed plant where the haploid egg develops * which will develop into a seed after fertilization
sori
fern structures in which spores are produced * The sori are found on the undersurface of the leaves, sometimes covering the entire undersurface and sometimes located at the edges
Monilophytes
ferns, horsetails, whisk ferns * As in seed plants, to which they are the sister group and side there is differentiation between a main stem and side branches *This patterns contrasts with the dichotomous branching characteristics of the lycophytes and rhyniophytes, in which each split gives rise to two branches of similar size
Streptophytes
group that includes green algae and land plants
Lycophytes
includes club mosses, spike mosses, and quillworts.
There are ten major groups of land plants
land plants - development from an embryo that is protected by tissues of the parent plant
pollen grain
male gametophyte in seed plants * pollen grains are released from the microsporangium to be distributed by wind or by an animal pollinator
antheridium
male reproductive structure in some plants that produces sperm
red algae - almost all are multicellular
marine algae in which the chlorophyll is masked by a red or purplish pigment
Ferns
member of vascular plants that reproduce via spores and have neither seeds nor flowers *Ferns appeared in the Devonian period. •Water is needed for transport of male gametes to the female gametes; most inhabit shaded, moist woodlands and swamps. •Sporangia are in clusters called sori.
gametangia
multicellular organs that produce gametes
Primary Endosymbiosis produced the first photosynthetic eukaryotes
primary endosymbiosis is shared derived trait- a synapomorphy of the group known as Plantae * Although Plantae is Latin for "plants" in everyday language and throughout this book the unmodified common name "plants" us usually used to refer only to the land of plants.
microsporangia
produce microspores that give rise to male gametophytes
microspores
produced by small male cones and will develop into male gametophytes or pollen grains (microgametophyte) that produces only sperm
phycoerythrin
red pigment in red algae * Their characteristic color is a result of the accessory photosynthetic pigment phycoerythrin, which is found in relatively large amounts in the chloroplasts of many red algae
Horsetails
seedless vascular plant with jointed stems; needlelike branches *15 species, all in the equisetum *The horsetails have reduced true leaves that form in distinct whorls (circles) around the stem
Gametes
sex cells
Mosses
soft, small, green and nonvascular and are found on the ground near water * 15,000 species found on damp, cool ground, where they form thick mats •Have stomata •Have cells called hydroids, which die and leave a channel through which water can move
Megasporangia
spore-producing structures that produce megaspores
Multicellular diploid plant is called
sporophyte
The two largest clades the monocots and the eudicots include:
the great majority of angiosperms species * The monocots are so called because they have a single embryotic cotyledon, whereas the eudicots have two.
Anther
the part of a stamen that contains the pollen.
stigma
the terminal surface that receives pollen grains
Vascular system
tissues specialized for transport of water and materials from one part of the plant to another *Vascular tissue allowed land plants to spread to new environments and diversify rapidly.
Ginkgos
trees with separate male and female plants. Pollen is produced in cones. The female tree produces fleshy-coated seeds. Ginkgo biloba is the only living member of this class
possess well-developed vascular systems that transport materials throughout the plant body called:
vascular plants, or tracheophytes because they all posses fluid-conducting cells called tracheids
A seed contains tissues from three generations:
•A seed coat develops from the diploid sporophyte parent (integument). •Haploid tissue from the female gametophyte provides nutrients for the developing embryo. •The embryo is the new diploid sporophyte generation. Seeds remain viable, have adaptations for dispersal Seeds are one of the major reasons for the evolutionary success of gymnosperms and angiosperms!
Four groups of gymnosperms:
•Cycads—tropical, earliest diverging clade •Gingkos—today only one species: Gingko biloba •Gnetophytes—Welwitschia, from Africa •Conifers—cone-bearing plants
Fruits develop from the ovaries after fertilization.
•Fruits protect seeds and aid in dispersal. •Some are eaten by animals or become attached to animals for dispersal.
Horsetails and ferns
•Independent sporophyte and gametophyte •Silica deposits in cell walls
The earliest vascular plants were homosporous:
•Like horsetails and many ferns.
Nonvascular plants: liverworts, mosses, hornworts •Live in moist habitats; have thin cuticles
•Live in moist habitats; have thin cuticles •Why are they small? - no vascular bundles •How are minerals distributed throughout their bodies? - diffusion •Which generation is photosynthetic? Dominant? - green part in moss - gametophyte •Gametes are produced in gametangia •The sperm must swim to reach the egg.
Earliest vascular plants (now extinct)
•No roots but had water-absorbing filaments, called rhizoids •Anchored in soil by rhizomes •Dichotomous branching pattern
Angiosperms
•Reproductive organs are in flowers; seeds are enclosed in fruits. •Multicellular female gametophyte very reduced—usually only 7-8 cells. •Pollination: Pollen from anther reaches stigma in different ways •Pollen tube delivers 2 sperm nuclei •Double fertilization results in embryo AND nutritive tissue called the endosperm