Diversity General

Plants are classified into 4 major groups: from simplest to most complex from oldest to most recently evolved (~15,000 species) small, simple, in moist habitats, oldest

Ferns (11,000 species) more complex tissues and organs,

Conifers (760 species) mostly and , reproduction by producing , and in “cones”

Flowering (235,000 species, 90% all plants) most complex in terms of structure reproduce by producing pollen, and seeds in

Plants: Plant Classification – General, Ziser, 2003 1 Mosses & Allies

(several other phyla of plants have the word “” in their common names but they are NOT really mosses they just resemble them in some way)

~15,000 species eg. mosses, liverworts, simplest of plants most are small (<20 cm) and inconspicuous grow along streams or on moist soil, rocks and trunks are ancient plants most are tropical they apparently developed from a green alga as a “dead end” group not in direct path of evolution (ie. vascular plants did not have moss ancestors) plants that were first able to leave aquatic environment and move onto land generally poorly adapted to land tend to live in moist places live in dense beds on moist soil, rocks or still tied to water for reproduction thin cuticle in most, some lack it no water distribution system: no vascular absorb water through (like ) no true , stems or (since no )

each individual plant has tiny -like for attachment (not to absorb nutrients for the plant)

slender stemlike structure bears leaflike blades

Plants: Plant Classification – General, Ziser, 2003 2 can grow upright or along ground weak (no lignin)

Reproduction and Cycle:

show basic alternation of generations with the dominant form in the life cycle it is larger it is often perennial while the is temporary it provides nutrition for sporophyte

gametophyte Structure (true mosses): leafy green often perennial bears gametangia at tip of “stalk” antheridia  sperm cells archegonia  eggs many species have separate male and female plants flagellated sperm are released from antheridia during rainy weather and transported by splashing of raindrops once they get to female plant, sperm swims down neck of and fuses with egg = the zygote grows into a sporophyte sporophyte remains attached to the gametophyte for nutrition foot = embedded in tip of gametophyte to anchor it seta = stalk

= – contains up to 50M haploid when spores are mature, capsule bursts open as it dries out or rain carry spores to new areas where they germinate

Ecological Importance:

Plants: Plant Classification – General, Ziser, 2003 3 Pioneer Plants colonize bare rock produce acids that help in soil formation hold soil in place and help prevent erosion along streams some (eg. waxwings) use moss as nesting material peat bogs: major carbon reserves eg. Sphagnum =>help to absorb CO2 and stabilize climate used for fuel in and some northern countries mosses are sensitive indicators of air pollution

Plants: Plant Classification – General, Ziser, 2003 4 and Allies (Seedless Vascular Plants)

Vascular Plants

virtually all plants other than mosses and allies have vascular tissue

vascular system enables plants attain greater size:  some ferns (tropical) grow to 75 feet today

vascular plants have true stems

most have vascularized roots and leaves

ancestors of vascular plants also evolved from green

Ferns & Allies

11,000 species

mostly terrestrial, a few are aquatic

range from tropics to arctic but most are tropical epiphytes

in temperate regions ferns typically inhabit swamps and moist areas

most common in the world is bracken fern (=Pteridium aquilinum)

grows well in poor soil – uncommon fern trait

have true stems, roots, and leaves

Stems

= underground stem with wiry roots

in temperate areas rhizome produces new leaves each spring

ferns are easily propagated by rhizome cuttings

Plants: Plant Classification – General, Ziser, 2003 5 Roots

the roots are clearly differentiated from stem

Leaves

frond = large, compound leaves used for and reproduction

when each young frond emerges from ground it is tightly coiled  fiddlehead

as fiddlehead grows it unrolls and expands to form frond

Reproduction and Life Cycle

ferns show clear alternation of generations

most ferns are annuals fern life cycle 4-18 months

sporophyte stage is dominant the “fern” we see are fern sporophytes are perennial

sporophyte produces asexual spores

production occurs on underside of in clusters of sporangia called sori

sometimes sori are covered by umbrella-like indusium [size of a pinhead]

as humidity changes sporangia break open throwing spores into air

Gametophyte Stage

gametophyte generation of ferns is completely separate and bears no resemblance to sporophyte

spores germinate into called a prothallium

Plants: Plant Classification – General, Ziser, 2003 6 gametophyte is tiny (~1/4 inch)

often heart shaped

as prothallium matures it produces male and female reproductive organs =antheridia & archegonia

archegonia located in central region near notch each contains a single egg antheridia scattered among rhizoids sperm cells shaped like screws

ferns require water for fertilization

as young sporophyte develops the prothallium withers and dies.

Ecological and Economic Uses of Ferns & Allies

help soil formation and prevent erosion

probably most significant contribution to human culture is as coal deposits  fern

are widely cultivated for horticultural value

the fiddlehead of some species are harvested in early spring , bilied or steamed and eaten esp in New England and eg. ostrich fern Matteaccia

horsetails have a hollow jointed stems impregnated with silica  gritty texture (=scouring rushes) first “brillo pads”

Plants: Plant Classification – General, Ziser, 2003 7 Plants mosses are small, nonvascular plants that generally are found in moist habitats and require water for reproduction ferns, though more terrestrial, with vascular tissue and better able to survive in drier habitats still require water for sexual reproduction

both of these groups are relatively rare today and found in only a few habitats. most plants today are Seed Plants  ( & angiosperms) seed plants are much more successful at life on land

1. they are no longer tied to water, even for reproduction

2. they generally have a much more efficient vascular system but most of their success can probably be attributed to three major adaptations:

1. Greatly reduced alternation of generations

sporophyte no longer produces spores for reproduction and dispersal

sexual reproduction becomes the primary method of reproduction and dispersal

instead sporophyte produces microscopic gametophytes that become the main means of reproduction and dispersal

2. Pollen

male gametophyte = pollen dispersed by wind (not water) to the female

Also offers a wider variety of methods of

Plants: Plant Classification – General, Ziser, 2003 8 genetic variation

3. Seed

female gametophyte remains attached to sporophyte plant as

once fertilized, ovule develops into seed

seed = embryonic plant

unlike spore which is a single cell, seed already has an embryonic root, stem and leaf

plus stored food supply for ,

surrounded by protective seed coat

in nonseed plants the asexual spore is the primary means of dispersal

seed replaces the spore as the main means of reproduction

is much more effective, and resistant to drying

in non-seed plants, the develops from the fertilized egg in the archegonium and immediately grows to maturity

in seed plants the embryo reaches a certain size, goes dormant, and becomes an important means of dispersal

Sexual reproduction becomes the main means of reproduction  greater variation  evolutionary advantage

seeds and seed plants are strongly connected with the development of human civilization as an important food source:

seeds are: easy to store easy to germinate

Plants: Plant Classification – General, Ziser, 2003 9 generally have high nutritional value

Plants: Plant Classification – General, Ziser, 2003 10 & Allies

760 sp of gymnosperms conifers are one of a group of plants called gymnosperms or “naked seeds” they produce seeds that are either totally exposed or borne on the scales of the female cone

the seeds are not produced inside a and they are exposed usually on a cone gymnosperms include: conifers: , cedar, , , sequoias, etc (resemble palms) ginkoes gnetophytes by far the most abundant gymnosperms are the conifers nearly all are woody trees, shrubs and conifers group contains some of the world’s a. most massive organisms: “General Sherman” giant - California 272’ (81.6m) tall 79’ girth; >25’ diameter

b. world’s tallest tree: Coastal Redwood 385’ (117m) tall

c. oldest living trees bristlecone one is over 4900 years old

Conifer Characteristics:

1. nearly all conifers are :

can carry out photosynthesis even in winter to some degree

Plants: Plant Classification – General, Ziser, 2003 11 in spring they can increase photosynthesis immediately (don’t have to grow new leaves)

each leaf 2-14 years and falls off individually

a few are , eg.: dawn redwood, , bald cypress

2. in most leaves are needle or scale shaped to survive dry conditions (desert, )

leaves are long, narrow, tough and leathery

most leaves have thick waxy cuticle

3. many conifers produce = viscous, clear organic substance that may protect plant from fungal and attack

resin collects in resin ducts = tubelike cavities that extend throughout roots, stems and leaves

resin is produced by cells lining resin ducts

Woody Stems

Conifers and flowering plants are the only major plant groups that have perennial species

Plants that live more than one year, ie. perennials, produce each year.

In woody plants there are two major layers of embryonic cells (lateral ) called the , that produces this secondary growth each year.

1. One layer of cambium is found in the vascular bundles of the stem between the and .

Each year this cambium produces new layers of xylem and phloem cells.

Xylem grows much faster than phloem and  virtually all of the “” of a tree is dead xylem cells

Plants: Plant Classification – General, Ziser, 2003 12 the oldest cells are closer to the center of the

Each year the cambium lays down a new layer of xylem

the old wood closest to the center expands as new cells are laid down in the vascular cambium

these older cells are often darker and are called heartwood.

vs sapwood (still used for transport)

Differences in the size of the cells produced throughout the growing season produce the familiar “growth rings” in the wood.

vs hardwood

the arrangement of different cell types in the secondary tissue results in the distinctive characteristics of each kind of wood: eg oak, maple, pine, etc

Most of the strength of wood comes from the sclerenchyma cells of the xylem specifically the tracheids, vessel elements and fibers

thickness of the trunk requires rays for lateral transport = chains of parenchyma cells that radiate out from center of stem typically continuous with the secondary xylem and phloem

the layers of phloem are much thinner and become part of the bark

The phloem, on the “outer-side” of the cambium, the cortex and the periderm make up the bark of a tree.

2. Another layer of cambium is located between the cortex and epidermis, this produces periderm

Plants: Plant Classification – General, Ziser, 2003 13 which makes up most of the bark of woody plants.

The bark replaces the epidermis for protection of the stem in large woody plants.

cork cambium can form a continuous cylinder of dividing cells (similar to vascular cambium in woody stems) or a series of small arcs  producing furrowed bark the thickness, patterns and texture of bark vary considerably by species largely because of the varying growth rates of cork cambium in different tree species

the bark contains cork cells dead at maturity heavily waterproofed cell walls protects against injury, mild fires, temperature extremes, water loss

areas of bark where cork cells are loosely arranged =  allow gas exchange wood is typically produced in the stem (=trunk) but major roots of trees also usually have wood, bark and annual rings

Life Cycle:

Mosses gametophyte was dominant sporophyte a temporary structure growing on gametophyte Ferns sporophyte was dominant, separate from gametophyte gametophyte was small temporary prothallium Conifers sporophyte is dominant plant gametophyte greatly reduced, temporary, and completely dependent on sporophyte

in gymnosperms the sporophyte is the dominant stage  there is no free living gametophyte instead, gametophyte is attached to and nutritionally dependent upon sporophyte Plants: Plant Classification – General, Ziser, 2003 14 both gymnosperms and angiosperms are heterosporous  produce two types of spores: most conifers are monoecious () with separate male and female cones in different locations of same plant reproductive organs are cones (=strobili)

Female Gametophyte

ovule – produced on female cone

female cone: much larger than male takes 2 years to mature not terminal

In early spring the ovulate or seed cone begins to develop Takes 2 years to develop consists of a central axis bearing a series of and scales (=modified leaves) two develop on upperside of each

some conifers do not produce woody female cones  eg. yews: seed is almost completely surrounded by fleshy cuplike covering, an outgrowth from base of seed seed covering is red and attracts birds which eat it and disperse the seeds  eg. bear seeds in fleshy cones that resemble fleshy scales are fused together and completely enclose seed birds eat and disperse seeds cones used to flavor gin

Male Gametophyte

=pollen grain produced in male cone

male cone: terminal on short branches

Plants: Plant Classification – General, Ziser, 2003 15 ~ half inch long or less produce pollen

consists of 2 cell walls enclosing 3 cells prothallial cells (2) degenerate) generative cell air sacs (for bouyancy)

tube cell

Pollen grains blow around until they contact micropyle of female gametophyte

Pollen tube develops from tube cell of pollen

generative cell produces sperm nuclei which travel down to egg and fertilize it = zygote the fertilized egg develops into mature seed consisting of several structures:

~8 cotyledons (surround epicotyl) seed coat hypocotyl

Economic Importance of Conifers:

conifers are the most important of gymnosperms both ecologically and commercially

conifers are the predominant trees in 35% of the world’s forests

they play an essential ecological role: 1. roots hold soil in place and reduce soil erosion 2. watersheds – absorb hold and slowly release water and help control flooding 3. food and shelter for other organisms coniferous forests are economically important:

1. recreation camping backpacking picknicing

Plants: Plant Classification – General, Ziser, 2003 16 2. in US ~80% of timber crop is from conifers:  building and paper products  landscaping  christmas trees resin of some plants is used to make , tar, etc

Plants: Plant Classification – General, Ziser, 2003 17 Flowering Plants [Angiosperms]

235,000 known species

=vascular plants that reproduce sexually by forming and fruits dominant plants in world today last major group to appear in the record 1st appeared 130 MY ago

have dominated the landscape for the last 100 Million years

Why are flowering plants so successful:

1. highly adaptable vegetative organs including complex symbioses with fungi and enhance survival

2. form and diversity of leaves maximize photosynthetic efficiency

3. much more efficient transport tissues structure of both xylem and phloem are more efficient than in gymnosperms

4. diversity in flower structure greatly enhances success and diversity of group

5. seed within fruit better protection much greater variety of dispersal

differences from gymnosperms: more efficient vascular tissues: sieve cells smaller in gymnosperms, larger and with more pores in angiosperms few gymnosperms have xylem vessels, mainly have tracheids angiosperms have flower instead of cone angiosperms surround seed with fruit

Two major groups of flowering plants: monocots ~65,000 species

Plants: Plant Classification – General, Ziser, 2003 18 flower parts in three’s parallel veined leaves onions, grasses, irises, lilies, only woody monocots are palms eg coconut palm

dicots more diverse, (>170,000 species) flower parts in 4’s or 5’s net veined leaves oaks, roses, mustards, cacti, sunflowers includes , shrubs and trees

Flower Structure

in flowering plants, sexual reproduction occurs in flowers = filament + anther pistils = + style +

are temporary structures

parts are arranged in whorls on the end of a flower stalk =

peduncle may terminate in a single flower or a cluster of flowers =

tip of peduncle enlarges to form the

sepals lowermost leaflike covers and protects flower all sepals together = calyx

petals whorl just above (inside) sepals great variation in size, shape and color sometimes fused to form tube all petals together = corolla

stamens just inside petals consist of filament and anthers

Plants: Plant Classification – General, Ziser, 2003 19 anther = sac like structure that produces pollen grains (=gametophytes)

each pollen grain produces 2 cells surrounded by tough outer wall one cell contains 2 male gamete (sperm) nuclei other cell  produces pollen tube through which sperm nuclei travel to ovule pistil female reproductive organs

may be a single chamber or made of a group of chambers = carpels

sometimes carpels are fused into a single pistil

sometimes there are many pistils

each pistil consists of: stigma  on which pollen lands style necklike structure ovary saclike, contains ovule

each ovule contains cells that form one egg and 2 polar nuclei many variations in flower structure a flower with all four different parts = complete flower lacking one or more = incomplete with both stamens and carpels = perfect stamens or carpels = imperfect some of these variations are due to the way flowers are pollinated pollen grains must travel from anther of one flower to stigma of another

self  pollen travels to stigma of same flower cross pollination  pollen travels to stigma of different plant flowering plants have coevolved with many kinds of through most of their history

this close interdependent relationship between

Plants: Plant Classification – General, Ziser, 2003 20 plants and has resulted in coevolution  mutual adaptations for mutual benefits plant: petals, scent, nectaries : special body parts and behaviors

In some instances the relationships have become very specialized such that only a single species of animal can pollinate a particular species of plant.

1. wind pollinated often grow in dense populations many small inconspicuous flowers petals reduced pistils and stamens exposed numerous stamens and conspicuous large amounts of pollen produced eg. oak, willow, grasses insect pollenators - general petals colorful and large often with nectaries fused petals force insect to crawl into flower for

2. sunflowers are a successful exception to above: they are insect pollinated but consist of numerous inconspicuous flowers they combine to resemble a single, large showy flower  one insect pollinates many flowers at once

3. bee pollinated 20,000 different species of bees are important pollinators for many plants honeybees are attracted to nectar they also gather pollen flowers are generally brightly colored predominately blue or yellow rarely pure red (pure red appears black to them) flowers often have lines or distinctive markings that function as “honey guides”  lead bees to nectar some of these markings are only seen in UV light

Plants: Plant Classification – General, Ziser, 2003 21  invisible to us, not bees flowers often delicately sweet and fragrant

4. pollinated flowers tend to have a strong yeasty, spicy or fruity odor usually white or dull in color ( cant see as well as bees) secrete no nectar but may supply food as pollen or in special storage cells in petals

5. carrion flies tend to be dull red or brown often have foul odors resembling rotting meat eg. carrion flowers (Africa); skunk cabbage

6. butterflies similar to bee-pollinated flowers in that they have sweet fragrances nectaries are usually at bases of deep spur that only butterflies and moths can reach with their mouthparts some butterflies can detect red flowers eg. daisy : butterfly bush= Buddelias, goldenrods, blazing star eg. milkweeds monarchs

7. moth pollinated white or yellow flowers heavy fragrance open at dusk

eg. some , some milkweds (see p510 Stern 3rd ed)

8. bat pollinated mainly in tropics strong odor dull color open only at night

9. hummingbirds do not have a highly developed sense of smell but do have excellent sense of vision frequently bright red or yellow flowers little if any odor fused petals with nectary

Plants: Plant Classification – General, Ziser, 2003 22 produce copius quantities of nectar long floral tubes prevent most from reaching the nectar eg. fuschias, petunias, morning glories, , cardinal flowers, trumpet creepers, columbines, penstemons

10. orchids some speceis of orchids resemble certain wasp females see Stern p 512-14

Plants: Plant Classification – General, Ziser, 2003 23 Role of Pollinators in Modern World

without pollinators many plants cannot be fertilized to produce seeds

90% of worlds flowering plants are animal pollinated including 80% of world’s 1330 cultivated crop species  1/3rd of US agricultural crops are insect pollinated

120,000 – 200,000 animal species are pollinators  including >1000 sp of birds and mammals honeybee pollination services are 60-100x’s more valuable than the honey they produce

in US ~1/2 of honeybee colonies have been lost in last 50 years  25% in last 5 yrs alone

threats: habitat fragmentation loss of nesting and overwintering sites intense exposure to pesticides and introduction of exotic species

Plants: Plant Classification – General, Ziser, 2003 24 Fertilization:

one of the two cells in pollen grain grows a thin pollen tube down through the style into the ovule

the 2nd cell divides to form two sperm cells which move down the pollen tube ad enter the ovule

only flowering plants have zygote

this double fertilization results in seed: young plant embryo nutritive tissue = endosperm seed coat

The Seed:

seed = plant embryo with stored nutrients in protective shell

mature seed consists of: 1. embryo: radicle = embryonic root hypocotyl = embryonic (stem) cotyledons = seed leaves (monocot has 1 dicots have 2 cotyledons) plumule (=epicotyl) = part of shoot above leaves

2. food food is stored either in the cotyledon or in endosperm (a nutritive tissue surrounding embryo)

the nutrients are used by the germinating seed until true leaves can begin photosynthesis

in monocots the endosperm is main source of food in mature seed in most dicots – endosperm nourishes embryo which subsequently stores food in its cotyledons

3. Seed Coat tough, for protection

Plants: Plant Classification – General, Ziser, 2003 25 seed size varies from: eg. dustlike  orchids eg. 60lbs  double coconut

The Fruit

seeds are not naked as in most gymnosperms

the ovary wall enlarges into a fruit  protects developing seeds from desiccation  aids in dispersal

As the ovule develops into a seed the ovary portion of the pistil increases greatly in size and becomes a fruit  fruit = a ripened ovary containing seeds

eg. pea pod = fruit; peas = seeds peach, bean and watermelon all develop from ovaries only 1/8th to 1/4th inch in diameter

causes great drain on food supply  vegetative growth often ceases when fruits are developing

pinching off some flower results in larger fruits that are left

The tissues of fruit and seed enhance survival and may aid in dispersal  distribute new plants to areas away from parent plant

There are many different kinds of fruits  characterized by how they develop and the arrangement of the flower parts that produced them

4 basic types: 1. simple: develops from a flower with single pistil eg. , grape, bean, pea, wheat, corn 2. aggregate develops from flower with may separate ovaries eg. rasberry, blackberry, 3. multiple develops from an inflorescence, ovaries fuse to form single

Plants: Plant Classification – General, Ziser, 2003 26 fruit eg. , mulberry, figs 4. accessory develop from flower in which receptacle or floral tube enlarges and becomes part of the mature fruit eg. apple, pears (=pomes  outer part of fruit is enlarged floral tube), strawberry (edible portion of strawberry is fleshy receptacle) most fruits are simple fruits at maturity simple fruits may be fleshy or dry fleshy: : eg tomato, brapes, blueberries, cranberries, drupe: contain hard stony pit surrounding single seed eg. peaches, plums, olives, avocados, almonds [NOT: strawberries, rasberries, mulberries] dry: some split open along seams or sutures to release seeds follicle: splits along 1 suture eg. milkweed legume splits along 2 sutures eg. peas, beans, bluebonnets capsule splits along multiple sutures eg. poppies, cotton, some do not split along sutures grain () single seed, seedcoat fused to fruit eg. corn, wheat achene same as grain but seed coat is not fused eg. sunflowers, daisies, composites nuts usually larger, often from compound pistil eg. , , hazelnuts [NOT: peanuts, brazilnuts

Seed Dispersal Mechanisms:

1. wind one of most important

Plants: Plant Classification – General, Ziser, 2003 27 a. small, light seeds eg. orchids  seeds resemble dust

b. hairlike appendages eg. dandelions, milkweeds

c. winged seeds eg. maple, bigonia

d. whole plant dispersal eg. (=Russian thistle)

2. edible fruits attracts birds or mammals may eat whole fruit or spit out pits if swallowed seeds resistant to digestive juices squirrels and birds bury fruits and seeds nuts stored underground are forgotten

3. passively carried by animals hooks or spines to catch in fur or on skin in mud on feet of birds, etc. burs, beggars ticks, devils claw, etc.

4. water dispersal aquatic plants rainfall some contain airsacs to float mangroves, coconuts

5. mechanical dispersal =explosive dehiscence seeds are forcibly ejected from fruit many cast seeds several feet away from parent plant eg. violets

Economic Value of Flowering Plants

virtually all crop plants are flowering plants

cooking oils

spices and seasonings

Plants: Plant Classification – General, Ziser, 2003 28 hardwoods are used for furniture and flooring musical instruments commercial products: latex/rubber maple syrup pharmaceuticals extracted nightshade  belladonna  atropine jimsonweed  scopolamine  hallucinogenic native Americans used for puberty rights and rituals

cork from bark of cork tree

baskets

paper

Plants: Plant Classification – General, Ziser, 2003 29