Gymnosperms

Cycads, Ginkgo, Conifers, and Gnetophytes

Gymnosperms

• Conifers, cycads, Ginkgo called gymnosperms
• Defining characteristics:
• Possess true vascular tissue and robust wood
• Seed-bearing plants (seeds in cones; not fruits)
• Pollen-bearing plants (pollen in male cones)
• Sporophyte is dominant
• Gametophyte smaller & dependent
• Conifers dominate in high latitudes/altitudes
• Uses: horticulture, construction, pulp
• About 1,000 species of gymnosperms
• Less than 100 genera in 14 families

naked

seeds

Conifer forests represent the largest carbon sink on Earth

Plant phylogeny

Gymnosperms are cone-bearing plants

Gymnosperms are also plants with seeds & pollen (=spermatophytes)

There are three groups of seed plants:

1. Cycads clade and many extinct gymnosperms
2. Conifer clade with Ginkgo & Gnetophytes (& extinct groups)
3. Flowering plants (session 5)

Seeds

Green algae

Bryophytes

Lycophytes

Ferns / Horsetails

Gnetophytes

Flowering plants

Conifers

Cycads

Ginkgo

Seed Plants

Gymnosperms

What is a Cone?

• Cones aggregate and protect seeds, but still allow direct pollination
• Seeds are considered “naked” (gymno-) because they are exposed to pollen
• Living gymnosperms always have separate male and female structures (unlike angiosperms)

Pinus, male

Pinus, female

Ginkgo, male

Cycad, female

Direct pollination

• Pollen lands directly on the ovule /seed
• Not on a stigma (like angiosperms)

Origin of the Seed

• The “seed” evolves from a sporangium-bearing ancestor…

… but how?

Sporangium

Sporangium

Spores

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MEIOSIS

MEIOSIS

Seed

?

In the beginning…�Homosporous, spore-bearing plant

Meiosis

Dispersal

• All spores functional and dispersed
• Female & male gametophytes are free-living

soil

Sporophyte

Gametophytes

All spores the same size and shape

…then,�Heterosporous, spore-bearing plant

Meiosis

Dispersal

• Plant that is heterosporous
• Female & male gametophytes
• Gametophytes remain in their spores
• Free-living sperm swims externally

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soil

A few large spores (♀), and many tiny spores (♂)

…then,�Seed-bearing plant

Pollen

Dispersal

1. Megasporangium is surrounded by a seed coat (=integument)
2. One megaspore is larger & not dispersed; Other megaspores dissolve
3. Female gametophyte is not released from the megaspore
4. Pollen (=microspores) land on ovule; male gametophyte released/grows
5. Pollen tube (=male gametophyte) releases sperm inside the ovule

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Ovule

or

Seed

♀

Meiosis

Female cone �“Ovuliferous”

♀

♀

Seed Coat

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Megasporangium

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Megaspore

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Female Gametophyte

A seed is a

“box-in-a-box” concept

Gymnosperm seed

Young Pine Seed x100

Male cone�“Staminate”

Pollen-bearing leaf

(sporophyll)

Pollen sac

Cone

Axis

Pollen

Conifers

• 66 genera, 589 species; largest diversity of gymnosperms
• Shrubs and trees; robust wood
• Needle-, scale-, and awl-shaped leaves
• Mostly evergreen
• Few deciduous in wetlands
• Xeric adaptations: sunken stomata & hypodermis
• Cone-bearing
• Large, woody ♀ cones
• Small, fleshy ♂ cones

Larix (larch or tamarack)

Taxodium (bald cypress)

Conifers have evolved into�extreme organisms

• Tallest, widest, heaviest, & oldest organisms on Earth
• 380.3 ft tall Coastal Redwood called “Hyperion”
• 48 ft diameter Montezuma Cypress called “Árbol del Tule”
• 2,300 tons Giant Redwood called “General Sherman”
• 4,857 years old Bristlecone Pine called “Methuselah”
• Germinated 2,833 BC!
• “Living fossil” Wollemi Pines discovered alive in 1994

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Conifers�(Coniferophyta)

Pines (Pinaceae)

Spruce (Picea)

Fir (Abies)

Douglas fir (Pseudotsuga)

Hemlock (Tsuga)

Pine (Pinus)

Conifers�(Coniferophyta)

Umbrella pines (Sciadopityaceae)

Umbrella pine (Sciadopitys verticillata)

Do you remember this plant from BOT315 – Stem Lecture?

Podocarps (Podocarpaceae)

Dacrydium

Celery pine (Phyllocladus)

Parasitaxus

Buddhist pine (Podocarpus)

Do you remember this plant from BOT315 – Stem Lecture?

Conifers�(Coniferophyta)

Araucarias (Araucariaceae)

Norfolk island pine (Araucaria)

Kauri pine (Agathis)

Wollemi pine (Wollemia)

Conifers�(Coniferophyta)

Cypresses (Cupressaceae)

Giant redwood

(Sequoiadendron)

Dawn redwood

(Metasequoia)

Junipers

(Juniperus)

Cypress-pine (Callitris)

Arborvitae

(Thuja occidentalis)

Redwood (Sequoia)

Cedars (Cupressus)

Conifers�(Coniferophyta)

Yew conifers (Taxaceae)

Plum yew (Cephalotaxus)

Torrey pine (Torreya)

Yews (Taxus)

Catkin yews (Amentotaxus)

New Caledonia yew (Austrotaxus spicata)

Conifer Lifecycle�

Male Cone

Female cone

Conifer Lifecycle – Spring�

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Cone stem

Cloud of

pollen

Ovule

Pollen tube

(male gametophyte)

♀

Embryo

Fertilization

Cone scale

Meiosis

Conifer Lifecycle- Summer/Fall�

Wing

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Wing

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Seed

♀

Embryo

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Cone stem

Conifer Lifecycle - Winter�

Wing

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♀

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Cone stem

Seed

Conifer Lifecycle - Spring�

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Cone stem

Seed

Cycads (or sago palms)

• 11 genera, 289 species
• Stems underground or trunk-like
• Palm-like appearance
• Largest apical meristem
• Largest plant pith
• Rigid, compound fronds
• Sharp cataphylls on trunk
• Coralloid roots contain cyanobacteria
• Dioecious plants
• Large male & female cones
• Largest cones in plant world
• Beetle pollination
• Motile sperm
• Largest sperm in plant world

Zamia integrifolia

Encephalartos woodii is extinct in the wild

• Only male plants exist in captivity

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Zamia integrifolia is the USA’s only native cycad

• Grows in Florida Keys and Georgia
• Status is “Near threatened”

Cycas revoluta

Encephalartos woodii

Ginkgo or �Maidenhair tree

• 1 species, Ginkgo biloba;
• Ginkgoes were diverse

during dinosaur age

• Conifer-like architecture: pyramidal
• Short-shoots & long-shoots
• Fan-shaped, deciduous leaves
• Male (pollen) cones
• Ovules paired on stalks; no cones
• Large, pulpy seed
• Contains butyric acid
• Common street tree
• Resistant to most pests and pollution

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Ginkgo adiantoides existed in North America until 7 million years ago; in Europe until 3 mya!

Ginkgo adiantoides

Ginkgoes may have been one of the first deciduous trees on Earth

Oldest Ginkgo in USA is located at Bertram Gardens in Philadelphia; planted c. 1785

Ginkgoes were probably dispersed by dinosaurs or early birds

Gnetophytes

• 3 genera, 68 species
• Ephedra, Gnetum, Welwitschia
• Vessels in wood (xylem)
• Complex venation patterns in leaves
• Flower-like cones with sterile bracts
• Angiosperm-like seed (Gnetum)
• Double fertilization (Gnetum & Ephedra)

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• Desert-adapted
• Reduced leaves
• Source of ephedrine & pseudoephedrine

• Large tropical liana
• Angiosperm-like leaves
• Seed w/ pulpy seed coat

Gnetum: Gnemon

Ephedra: Mormon’s Tea

Welwitschia: Tree Tumbo

• Grows in Namibian desert
• Only 2 leaves entire life
• Remember from Leaf lecture?

Double fertilization: 2 fertilization events

1. A sperm fuses with an egg 🡪 embryo
2. A sperm fuses with another cell 🡪 endosperm

Endosperm becomes “food” for embryo

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Angiosperms also do this!

Gymnosperm Lab

Pine (Pinus): Female cone (prepared slide)

• Whole cone (x40): Cone scale(s), Ovule(s)
• Ovule (x400): Seed Coat, Mega-sporangium, Megaspore wall, Female gametophyte

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Pine (Pinus): Male cone (prepared slide)

• Sporophyll(s), Pollen sacs, Pollen

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Maidenhair tree (fresh material) - Ginkgo biloba

• Leaves, Long shoots, Short shoots

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Cone Scale

Female cone x40

Male cone x40

Ovule x100

Sporophyll

Pollen

sac

Pollen

Ovule

Ovule

Ovule

Cone Scale

Cone Scale

Cone Scale

Ginkgo

Zamiaceae

Cycadaceae

Sago palm (Cycas)

Coonti (Zamia)

Bread trees (Encephalartos)

Dioon