Ch5 Evolution of Woody and Seed Plants

8/3/2019 Ch5 Evolution of Woody and Seed Plants

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Chapter 5

Evolution of Woody andSeed Plants

Michael G. Simpson


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Evolution ofwood from

secondary xylem of

vascular cambium

enabled plants to growvery tall, as large trees.

Illustrated: Sequoiadendron giganteum, giant

sequoia, largest non-clonal organism on

earth; most tissue dead secondary xylem

(wood).


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Divisions ofvascular cambium mostly tangential (some radial)

2 xylem > inside, 2 phloem > outside: bifacial growth.


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Secondary growth from lateral meristems:

vascular cambium & cork cambium.

Vascular cambium: 2 xylem > inside; 2 phloem > outside:

= bifacial growth.

Tissue to outside (cortex, older 2 phloem) gradually crushed.


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In most temperate regions (growth season / winter) and some tropical

regions (dry/wet season), seasonal annual rings form.

Annual rings can be used to date wood.

Dendrochronology study of wood in relation to time and

environment/climate.


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cork cambium

- like vascular cambium bifacialcork> outside, phelloderm> inside


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Seed

= embryo enclosed by nutritive tissue,

surrounded by seed coat

Ovule

= immature seed (prior to

fertilization/maturation)


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Seed Evolution


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Heterospory


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micropyle hole in integument,

where pollen enters (gymnosperms)

telomes & lagenostome found in

fossil (extinct) taxa, functioned in

pollen capture

pollination droplet secreted frommicropyle; pollen grains stick to, are

pulled inside as droplet evaporates.

Ginko biloba


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Pollen grains develop from microspores by mitotic divisions/differentiation.

[When haploid nucleus ofmicrospore starts to divide mitotically, it becomes a pollen grain.]

Pollen grains = immature endosporic male gametophytes


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Pollen tube haustorial (parasitic, feeding off tissues) in Gymnosperms

-In cycads & Ginkgo sperm delivered to fertilization chamber, wheresperm swims to archgonium = zooidogamy.

-In conifers (incl. Gnetales) tube grows directly to archegonium =

siphonogamy.

Pollen tube exosporic, tube-like extension frompollen grain.


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Ovule development


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Adaptive significance ofseeds

1) Protection ofembryo (seed coat)

2) Nutrition ofembryo (nutritive tissue=female

gametophyte in Gymnosperms)

3) Dispersal unit(e.g., fleshy, carried by animals; winged,

transported by wind)

4)D

ormancy mechanisms (seed coat inv

olv

ed inpreventing germination except when conditions right)


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eustele single ring ofvascular bundles


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Archeopteris large tree, wood

like a conifer, leaves like a fern;

some heterosporous.

Medullosa a tree fern, bore

seeds, but with fern-like foliage.

Two fossil (extinct) lignophytes:


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Gymnospermae (naked seed) seeds not enclosed by carpel;

sister to Angiospermae.


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Cycadophyta - Cycads


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Cycadophyta Cycads

-trunks short(rarely elongate, tree-like)

-leaves pinnate (rarely bipinnate),

coriaceous, with circinate

vernation (like ferns)

-dioecious (separate male & femaleindividuals)

-sperm motile


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Cone = determinate shoot systems, consisting of a single axis

with sporophylls = modified leaves with attached sporangia.

Pollen cones (male) bear

microsporophylls, with

microsporangia.

Ovulate / seed cones

(female) bear

megasporophylls,

with ovules/seeds.

pollen cone

seed cone


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Cycadophyta Cycads

Cycadaceae:

female plantswithout cones;

seeds born on

megasporophylls

from stem axis.

One genus: Cycas

Cycas revoluta

sago-palm-starch derived from

pith > flour, bread.

[C. media

-edible seeds]


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Cycadophyta Cycads

Zamiaceae:

female plantswith seed

cones;

leaves pinnate

or bipinnate


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Cycadophyta Cycads

Zamiaceae:

female plantswith seed

cones;

leaves pinnate

or bipinnate


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Ginkgophyta Maidenhair Trees

One family:GinkgoaceaeMaidenhair Tree

family

One species

(monotypic):

Ginkgo biloba


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Ginkgophyta - Ginkgo biloba

- tree with short shoots

- leaves obtriangular

- venation dichotomous

- dioecious


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Ginkgo biloba

Pollen cones catkin-like: axis bearing stalk-like

microsporophylls, each with two microsporangia.


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Ginkgo biloba

Ovulate reproductive structures: stalk bearing two, erect

ovules, each with basal collar. Seeds fetid (butyric acid).


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Coniferae conifers

Apomorphy:pollen tubesiphonogamous

-leaves simple

Three groups:

Pinopsida

Cupressopsida

Gnetales


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Pinaceae: Pinus


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Mystery of the conifer cone: compound


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Evolution ofthe conifer cone:

Compound structure (axis bearing two components):

bract homologous with leaf

ovuliferous scale homologous with shoot system


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Coniferae conifers

P

inopsida:

One family:

Pinaceae


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Pinaceae

-pollen cones with

2 microsporangia

/ microsporophyll

-pollen grains of

some taxa saccate

(with 2 bladders)


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Pinaceae

-seeds usu. 2 per

ovuliferous scale,

inverted, winged.


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Pinaceae

-leaves linear to acicular

(needle-shaped)

- in some taxa,

short shoots

(e.g., Cedrus)

or

determinate fascicles

(Pinus).


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Pinaceae

Include:

Abies fir

Cedrus cedar

Larix larchPinus pine

PseudotsugaDouglas-

fir

Tsuga - hemlock


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Coniferae conifers

Cupressopsida

5-6 families

We will cover 4:

Araucariaceae

Podocarpaceae

Cupressaceae

Taxaceae


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Araucariaceae

-leaves broad to acicular

-microsporangia

numerous (5-20) permicrosporophyll

-ovule 1 per scale

Includes:Araucaria heterophylla

Norfolk Island-Pine

Araucaria bidwillii

bunya-bunya

Agathis australis

kauri

C


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Cupressaceae

-leaves linear, acicular, or

subulate, spiral, opposite,or whorled

-branches flattened in

some, resembling pinnate

leaves in some

-seed cones with numerous

seeds per scale (2-20)

-pollen not saccate

Includes:

Cupressus cedar

Juniperus -juniper

Sequoia sempervirens

redwood

Sequoiadendron giganteum

giant sequoia

Taxodium bald-cypress


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Podocarpaceae

-leaves linear, elliptic, or

subulate

-seed cones usu. fleshy,

often reduced, in some

subtended by fleshy

receptacle, seed may be

enveloped by fleshy

epimatium derived from

scale

Includes:

Podocarpus, e.g., P.

gracilior

Phyllocladus spp.


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Taxaceae

Yew family

-seed cones usu.

reduced to 1 ovule

-seed surrounded by

fleshy aril

Includes:

Taxus yew

taxol derived from T.

brevifolia, used to treat

ovarian cancer

C if if


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Coniferae conifers

Gnetales:

3 families:

Ephedraceae

Gnetaceae

Welwitschiaceae

All dioecious


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Gnetales:

Apomorphies:

1)Pollen striate

2)Vessels porate


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Gnetales

Gnetaceae

One genus: Gnetum (ca. 30 spp.)

Gnetum tropical vines [trees, shrubs],

leaves simple, opposite


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Gnetales

Ephedraceae

One genus:

E

phedr

a (35-45 spp.)Morman Tea


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Ephedra Morman-TeaShrubs

Deserts of S.W. North America,

W. South America, N. Africa, and Eurasia


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Ephedra

- pollen coneswith stalk-like

microsporan-

giophore,

bearing

synangia

- seeds of seed

cones with

fleshy, connate

bracteoles and

micropylar

tube


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GnetalesWelwitschiaceae

One genus/species:

Welwitschia

mirabilis

-native to deserts

ofNamibia


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Ch5 Evolution of Woody and Seed Plants