Gymnosperms
Gymnosperms
Gymnosperms
Spring 2010
Outline
Review of land plant phylogeny
Characters of seed plants
Gymnosperm phylogeny & diversity
Gnetophytes
Cycads
Gingko
Conifers
Review of land plant phylogeny
Angiosperms
Flowering Plants
nonmotile
sperm
loss of lateral
branches
and MORE!
vessel structure
striate pollen
Seed Ferns
double fertilization [FOSSIL]
nonmotile sperm
eustele
axillary branching
vascular cambium [secondary xylem (wood) & secondary phloem) & cork cambium (cork)
seed: MANY CHARACTERS! e.g., heterospory; reduction/retention of megaspore; integument/micropyle; nutritive tissue
Characters of seed plants
Eustele
Axillary branching
Wood
Cambia (vascular cambium, cork cambium)
Seed
Heterospory
Megaspore reduction/retention
Integument/micropyle
Nutritive tissue
Male gametophyte
Pollen grain
Pollen tube
Characters of seed plants: Eustele
Megaspore reduction/retention
Integument/micropyle
Nutritive tissue
Life cycle of most seed-free plants
homospory
Multicellular
Sporophyte
[with sporangia]
Zygote
2n
SYNGAMY alternation of MEIOSIS
generations
n
Spores
Gametes
[egg + sperm] Multicellular
Gametophyte
[with gametangia:
archegonia + antheridia]
Life cycle of seed plants
heterospory
Multicellular
Sporophyte
Zygote
2n
SYNGAMY alternation of MEIOSIS
generations
n
microspores
sperm Male Gametophyte
egg [antheridia] megaspores
Female Gametophyte
[archegonia]
Evolution of the seed
Megaspore reduction:
-reduction to 1 megaspore
Evolution of the seed
Megaspore retention:
-the one megaspore is retained within
megasporangium, not released
Evolution of the seed
Evolution of integument/micropyle from
sterile sporophyte tissue
Evolution of the seed
pollination droplet:
-secreted by young ovule through micropyle
-water + sugars, amino acids (megasporangium)
-adhering pollen grains pulled inside!
Evolution of the seed
-nutritive tissue from the
female gametophyte
-integument becomes the
seed coat
Figure 7.11 (Pt. 2) from the text
Characters of seed plants
male gametophyte
pollen grain = extremely reduced male
gametophyte, a few cells
pollen tube formed by the pollen, grows
though sporophytic tissue to deliver sperm
cells to egg (in ovule)
Characters of seed plants: seed
Angiospermsmonophyly supported
by many characters including the
carpel
Gymnosperm Phylogeny
Gymnosperms
paraphyletic Gymnosperms
monophyletic
Gymnosperms Gymnosperms
monophyletic paraphyletic
Gymnosperm diversity
-ca. 15 families, 75-80 genera, ca. 900 species
-4 monophyletic lineages
-all woody
-mostly without effective vegetative reproduction
-only tracheids in the xylem (except for gnetophytes,
which also have vessels)
-naked seeds
-relatively slow sexual reproduction
-worldwide but dominant in many colder or arctic
regions
-include the tallest, the most massive, and the longest
living individual plants
Major groups of gymnosperms
Gnetophytes
Cycads
Gingko
Conifers
Major groups of gymnosperms
GnetophytaGnetophytes or Gnetales
3 extant genera: Ephedra (65 spp.); Gnetum (28
spp.); Welwitschia mirabilis
related to angiosperms?
recent molecular data: a gymnosperm group
defined by many characters, e.g.:
-opposite leaves, similar pollen
-vessel structure (independent of angiosperms)
-nonmotile sperm (independent?)
-double fertilization (independent of angiosperms)
-some with insect pollination
Major groups of gymnosperms
Gnetophyta - Gnetophytes
Welwitschia mirabilis
-a strange plant native to deserts of Namibia,
sw Africa!
-2 big curly leaves!
Major groups of gymnosperms
Cycadophyta Cycads
squat, unbranched trunk (little wood),
usually pinnately compound leaves
loss of axillary branching
dioecious: male and female plants
male and female strobili (cones)
motile, multiflagellate sperm!
(ancestral)
coralloid roots with nitrogen-fixing
cyanobacteria
Major groups of gymnosperms
Cycadophyta Cycads
ca. 11 genera (130 spp.)
now restricted distribution
seeds with bright fleshy seed
coat--dispersed by plant-eating
dinos!
A native U.S. cycad:
Zamia floridana
Major groups of gymnosperms
Ginkgophytes Ginkgo
extensive fossil record butonly
1 living species: Ginkgo biloba!
Coniferophyta Conifers
ca. 600 spp.
once dominant worldwide, displaced by angios
shrubs or small trees, highly branched with
well developed wood
leaves simple, often needle-like or awl-shaped
-pines: in fascicles
non-motile sperm (pollen tube needed)
female (seed-bearing) cones in most
Major groups of gymnosperms
Coniferophyta Conifers
female
Major groups of gymnosperms
Coniferophyta Conifers
seed cone and pine nuts
Conifers
Pollen usually with 2 appendages
Resin canals in
wood & leaves
Pinaceae
Abies (fir)
-needles in bundles
-cone scales thickened at
the tip and often armed
with a prickle
Pollen without appendages Leaves scale-like to linear
Chamaecyparis
Sequoia sempervirens (redwood) Sequoiadendron giganteum
(giant sequoia)
Taxaceae
Ovules solitary,
cones lacking
Araucariaceae