1. Seed Plants & Gymnosperms
Spring 2014

2. Outline Review of land plant phylogeny Characters of seed plants
Gymnosperm phylogeny & diversity
Cycads
Gingko
Conifers
Gnetophytes

3. Review of land plant phylogeny
Green plants (viridophytes)
Land plants (embryophytes)
Vascular plants (tracheophytes)
Seed plants (spermatophytes)
Gymnosperms
Angiosperms

4. Fig. 5.1
Evolution of
wood before
the evolution
of seeds.

5. Fossil lignophytes Progymnosperm (wood, no seeds) Seed fern
(wood, seeds)

6. Seed fern fossils from Pella, Iowa

7. Fig. 5.1 Evolution of wood (>380 mya) before the evolution
of seeds (>360 mya).

8. Characters of seed plants
Eustele (ancestral)
Axillary branching
Wood (ancestral)
Cambia (vascular cambium, cork cambium)
Seed
Heterospory
Megaspore reduction/retention
Integument/micropyle
Nutritive tissue
Male gametophyte
Pollen grain
Pollen tube

9. Characters of seed plants: Eustele
eustele = primary stem vasculature comprising a
single ring of vascular bundles

10. Characters of seed plants: axillary branching
Bud/branch traces
Leaf traces

11. Characters of seed plants: cambia
cambia: vascular cambium (wood) & cork cambium (periderm)
Fig. 5.3

12. Fig. 5.4
X-section of woody stem

13. Characters of seed plants: seed
Heterospory
Megaspore reduction/retention
Integument/micropyle
Nutritive tissue

14. Life cycle of most seed-free plants
homospory
Multicellular
Sporophyte
<
embryo
cells in
sporangium
[with sporangia]
Zygote
< 2n
<
alternation of
generations
SYNGAMY
MEIOSIS
< n
<
Spores
Gametes
[egg + sperm]
Multicellular
Gametophyte
<
<
<
[with gametangia:
archegonia + antheridia]

15. Life cycle of seed plants
heterospory
Multicellular
Sporophyte
<
embryo
megasporangia
Zygote
<
microsporangia
< 2n
<
alternation of
generations
SYNGAMY
MEIOSIS
< n
<
microspores
<
sperm
Male Gametophyte
egg
<
[antheridia]
megaspores
<
<
Female Gametophyte
[archegonia]

16. Evolution of the seed Megaspore reduction: -reduction to 1 megaspore
Fig. 5.6 #3

17. Evolution of the seed Megaspore retention:
-the one megaspore is retained within
megasporangium, not released
Fig. 5.6 #4

18. Evolution of the seed Evolution of integument/micropyle from
sterile sporophyte tissue
Fig. 5.6 #5

19. Evolution of the seed pollination droplet:
-secreted by young ovule through micropyle
-water + sugars, amino acids (megasporangium)
-adhering pollen grains pulled inside!
Fig. 5.10

20. Evolution of the seed -nutritive tissue from the female gametophyte
-integument becomes the seed coat
Fig. 5.10

21. 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)
Pine pollen

22. Characters of seed plants: seed
Adaptive advantages of the seed:
protection (seed coat)
dispersal unit of sexual reproduction
dormancy mechanisms
nutritive tissue – provides energy for young
seedling, aiding in establishment

23. Two major groups of seed plants:
Gymnosperms—not sure of the early evolutionary history of gymnosperms; could be monophyletic or could be paraphyletic
Angiosperms—monophyly supported by many characters including the carpel

24. Gymnosperm Phylogeny Cycads Gingko Pines Gnetales Cypresses et al.
pollen tube
compound ♀
cones (strobili)
simple leaves
1° DNA data

25. Gymnosperm diversity -ca. 15 families, 75-80 genera, ca. 1,000 species
-4 or 5 main 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

26. Gymnosperm wood: tracheids only

27. Major groups of gymnosperms
Cycads
Gingko
Conifers
Gnetophytes

28. Major groups of gymnosperms Zamia female strobilus
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
Zamia female strobilus
Cycas male
strobilus

29. 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!

30. A native U.S. cycad:
Zamia floridana

31. Gymnosperm Phylogeny Cycads Gingko Pines Gnetales Cypresses et al.
pollen tube
compound ♀
cones (strobili)
simple leaves
1° DNA data

32. Major groups of gymnosperms
Ginkgophytes – Ginkgo
extensive fossil record but…only
1 living species: Ginkgo biloba!
highly branched tree with
well developed wood
deciduous, fan-shaped leaves with
dichotomous venation
dioecious: male and female trees
-male: “cone” with lateral stalks bearing
microsporangia
-female: no cone, axis with 2 ovules
(outer integument layer fleshy)
motile sperm (ancestral)

33. Major groups of gymnosperms
Ginkgophytes – Ginkgo

34. Fig. 5.1

35. Major groups of gymnosperms
Coniferophyta – Conifers
ca. 700 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
include both traditional conifers but now also the Gnetales (gnetophytes)

36. Major groups of gymnosperms
Coniferophyta – Conifers
pollen cone or male cone
-microsporangia & modified leaves
seed cone or female cone
-axis with modified leaves (bracts, usually reduced), each subtending seed-bearing scale (modified branch system)
-woody or leathery or fleshy
male
female

37. Major groups of gymnosperms
Coniferophyta – Conifers
seed cone and pine nuts
Stone Pine nuts
[w U.S.]
Korean pine nuts

38. Evolution of the compound conifer female cone
Fig. 5.19

39. Gymnosperm Phylogeny Cycads Gingko Pines Gnetales Cypresses et al.
pollen tube
compound ♀
cones (strobili)
simple leaves
1° DNA data

40. Pinaceae Pollen usually with 2 appendages Leaves linear to needle-like
Resin canals in
wood & leaves
Pinaceae
Winged seeds
Ovules 2, inverted

41. Pseudotsuga (Douglas fir)
Abies (fir)
Picea (spruce)
Larix (larch)

42. Pinus (pines) -needles in bundles -cone scales thickened at
the tip and often armed
with a prickle

43. Gymnosperm Phylogeny Cycads Gingko Pines Gnetales Cypresses et al.
pollen tube
compound ♀
cones (strobili)
simple leaves
1° DNA data

44. Cupressaceae Pollen without appendages Leaves scale-like to linear
Cone scales fused to bracts
Microsporangia 2-10 per microsporophyll &
ovules 1-20 per cone scale
Cupressaceae

45. Juniperus (juniper)
Taxodium (bald cypress)
Chamaecyparis

46. Sequoiadendron giganteum
Sequoia sempervirens (redwood)
Sequoiadendron giganteum
(giant sequoia)

47. Taxaceae Ovules solitary, cones lacking
Seeds with a fleshy, brightly colored aril

48. Podocarpus
Araucariaceae

49. Gymnosperm Phylogeny Cycads Gingko Pines Gnetales Cypresses et al.
pollen tube
compound ♀
cones (strobili)
simple leaves
1° DNA data

50. Major groups of gymnosperms
Gnetophytes 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

51. Major groups of gymnosperms
Gnetophyta - Gnetophytes
Ephedra (65 spp.)
-common desert shrub
-reduced
scale-like
leaves

52. Major groups of gymnosperms
Gnetophyta – Gnetales
Gnetum (28 spp.)
tropical vines, trees, shrubs with opposite leaves that look like angiosperms!

53. Major groups of gymnosperms
Gnetales – Gnetophytes
Welwitschia mirabilis
-a strange plant native to deserts of Namibia,
sw Africa!
-2 big curly leaves!