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

Plantae

Streptophyta

Viridiplantae

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

Apicalmeristemof shoot

Developingleaves

100 µm

Apical meristems of plant shoots and roots. The light micrographs are longitudinal sections at the tips of a shoot and root.

Apical meristemof root

Root100 µm

Shoot

Apical Meristems

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 LycophytaClub 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

DivisonGingkophyta

Gingkobiloba

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