Cycads and Cyacadeoids

Bot. 313: Lecture 13
Cycads and Ginkgo
Cycads & Ginkgo
among
seed plants
Seed Plants
Angiosperms
1. Seed Ferns
2. Cycads
3. Ginkgo
4. Conifers
5. Gnetophytes
6. Flowering Plants
Ginkgo
Cycads
Gnetales
Mesozoic “The Age of Cycads”
Order: Cycadales
• Family: Cycadaceae- 9 living genera
Genus: Cycas
• Family: Stangeriaceae
Genus: Stangeria
Genus: Bowenia
• Family: Zamiaceae
Genera: Zamia, Ceratozamia,
Microcycas, Encephalartos,
Macrozamia, Lepidozamia
Cycad characters
• Fern-like leaves—pinnate (use fern terminology) –
petiole, rachis, pinnae
• Thick stems with armor of bracts & leaf bases
• Manoxylic wood = large pith, wide cortex, spongy wood
with lots of parenchyma, fewer tracheids
• Coralloid roots
• Microsporangia borne on abaxial surface of modified
leaves = sporophylls, helically arranged on the axis of
simple pollen cones
• Seeds borne on modified leaves= sporophylls organized
into cones (except the genus Cycas)
Growth Form
&
Stem
Cycas
Macrozamia
Zamia
Bowenia
with
bipinnate
leaf
Cycas
Naked
seeds on
sporophylls
Plants are
Dioecious=
“2 houses”
i.e., either
produce
seeds or
pollen
Encephalartos horridus
Stem Anatomy
Pith
Stele with
Manoxylic wood
Cortex
Leaf Form
Zamia
Stangeria
Encephalartos
Encephalartos
horridus
Ceratozamia
Zamia
Cycas leaf showing xeromorphic adaptations
sunken
stomata
thick cuticle
Coralloid roots
Cyanobacteria
in coralloid
root cortex
Pollen Cones
Encephalartos
Encephalartos
pollen cone
Zamia
pollen cone
Microsporangia = pollen sacs
Zamia pollen grains with microgametophytes
Megasporophylls
&
Seed Cones
Cycas circinalis
Megasporophylls
Seeds
Pollen Cone
Cycas
Cycas megasporophylls
Cycas megasporophylls
Zamia seed cones
Zamia seed cones (ovulate)
Zamia seed cone
Zamia seed cone
Seed with mature
embryo
embedded in
megagametophyte
tissue
Ovule Development
&
Seed Structure
(white board diagrams)
Zamia
Immature
nucellus, integument ,
meiosis, & micropyle
Small
Zamia
Somewhat more mature
nucellus, integument ,
free nuclear megagametophyte,
megaspore membrane,
some integument differentiation
Somewhat
larger
(note: non-medial section does not
pass through micropyle)
Micropyle
Integument
Nucellar apex with pollen tubes
Nucellus
Archegonial chamber
Archegonium
Megagametophyte
Zamia mature ovule l.s.
Cycad mature integument
sarcotesta
sclerotesta
endotesta
megagametophyte
Full size!
Cycad mature ovule with pollen in nucellus
Apex of nucellus
showing pollen
tubes
Sperm with
many flagella
Embryogeny
(embryo development)
(white board diagrams)
Ginkgo biloba
– Order: Ginkgoales
• Ginkgo biloba – 1 sp. China & Japan (any native?
Temple grounds - now cultivated world wide) - trees
Ginkgo biloba – maidenhair tree
A “living fossil”
Ginkgo- the living fossil
• Known first in the western world as fossils
• Found to be growing in China on temple
grounds
• May have become extinct in the wild, but now
planted everywhere in temperate regions
• Resistant to pollution and fungal attack
• Grown on roadsides in Japan and thrives on
carbon monoxide (leaves greener over streets
with traffic)
• Permian-Recent (ginkgophytes)
Ginkgo
Has characteristics of both cycads and conifers
– Conifer-like
• Wood- pycnoxylic
• Large tree-sized plants
• Long & short shoots
(some conifers)
– Cycad-like
• Dioecious (some conifers too)
• Simple pollen cones
• Swimming sperm
• unique-fan-shaped deciduous leaves
• distinctive ovulate stalks
• reproductive structures on short shoots
Ginkgo ovules
Ginkgo ovules
Structure, growth,
development,
pollination, &
sperm like cycads
Ginkgo pollen bearing cones
Simple cones with sporophylls that bear two nearterminal pollen sacs on abaxial side of stalk
Ginkgo biloba
and
ginkgophyte leaf evolution
Long shoot leaf
Short shoot leaf
Sucker shoot leaf
Ginkgo leaf evolution
& venation
Progressive webbing
(Telome Theory)
Republic, Was
Triassic
Jurassic
Cretaceous/
Eocene
(long shoot)
Forking veins
Living
(Short Shoot)
Living Seed Plant Clades