Gymnosperms

naked seed

Four major living groups.

Cycads (Cycadophyta),

Welwitschia group (Gnetophyta),

Ginkgo, the Maiden Hair Tree (Ginkgophyta),

and the conifers (Pinophyta) .

Microcycas calocoma Photo Dennis Stevenson

Cycads resemble palms or tree-ferns in overall appearance but differ greatly in detailed structure and reproductive behaviour. Cycads are dioecious (i.e. male and female reproductive structures are borne on separate plants), and reproduction is by seeds produced on open carpophylls or seed-bearing leaves. Although technically woody plants, unlike other woody plants, cycads have a thick, soft stem or trunk made up of mostly storage tissue with very little true wood. The living cycads include about 250 species, with 11 genera in 3 families.

Female cone

Cycads

Cuban species

Cycas bougainvilleana

Welwitschia mirabilis

Large, straplike leaves that grow continuously along the ground. During its entire life, each plant produces only two leaves, which often split into many segments as a result of the leaves being whipped by the wind. Carbon-14 datings of the largest plants have shown that some individuals are over 1500 years old.

Lives in coastal desert regions of Namibia and Angola. Morning fogs provide moisture.

Female cones Male cones

Gnetophyta

Ginko biloba

There are no native ginkgoes living in the wild.

Several ginkgoes were the only living survivors of the atomic bomb blast at Hiroshima

Illustration in Pen Tsao Kang Mu of Ginkgo with seeds (1578)

Medicinal!!

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The Evergreen State

Why is Washington called the

Evergreen State?

Evergreens have potential for growth all-year round

What is the advantage of the potential for all -year round growth?

Why aren’t all plants evergreen?

Why is so much of Washington covered by evergreen conifers?

What is the advantage of the deciduous habit over the evergreen habit?

Most conifers are evergreen

Evergreenness

What is the advantage of the potential for all –year round growth?

Opportunistic growth when conditions may be favorable and lack of dependence upon a particular time when growth must be made.

Why aren’t all plants evergreen?

Evergreen plants are frequently slow growing. The features that enable them to survive harsh conditions do not always enable them to grow quickly.

What is the advantage of the deciduous habit over the evergreen habit?

Deciduous plants are frequently faster growing than evergreen plants and can rapidly exploit favorable and reliable habitats. Leaves do not require to withstand severe cold and leaf abscission enables nutrients and carbohydrates to be withdrawn into the plant for re-use

Why is so much of Washington covered by evergreen conifers?

It regularly has periods of summer drought but mild wet winters. This can favor evergreens over deciduous trees.

In what other type of environment are evergreen conifers frequently found?

Time scale

Mos

ses

Fer

ns

Conifers

Ginkgos

Cycads

Gnetales

Origins of conifers in the Permian

AngiospermsRelative numbers of species of major groups of plant across geological time

The coal forming period

Millions of years

Pangea

In the Permian the land masses came together and formed a large

continent call PangeaCarboniferous

360 to 286 mya

Continental type climates typically have dry periods or seasonal rains. These can be seasonal and may be called

monsoons

Gymnosperms show adaptations to drier conditions than mosses and ferns both in their reproduction and vegetative growth

1.      Airborne male gametophyte (pollen) carried by wind to the female gametophyte where sperm fertilizes the egg located in the female gametophyte in the ovule which is retained, sustained and protected by the sporophyte.

2.      Production of a durable seed that at maturity consists of a protective seed coat, a source of nutrition and an embryo sporophyte all in one package.

3. Seed plants have wood producing tissue well developed in some species for water conduction and support. This enables plants to grow tall and out-compete neighbors

Adaptations for the drier environment

Reproductive

Vegetative

Reproduction in the conifers

The cone is a modified branch. Unlike the flower it does not have sepals or petals. Usually separate male and female cones are borne on the same plant, i.e., monoecious. Each of the numerous scales, or sporophylls, of the male cone bears pollen and each female cone scale bears ovules in which egg cells are produced. .

http://forest.wisc.edu/forestry415/INDEXFRAMES.HTM

Life cycle

Fig. 17.8

From ovule to seed

Cedrus deodora

Male cones – all lined up and ready to go!

The diminutive female cone

Developing seed cones

Pictures of male cone and pollen

Microsporangium

Pollen grains

Male cone

Continuing vegetative shoot

Pictures of female cone

Female cone

Longitudinal section through ovulate cone

Single scale (sporophyll

Ovule

Megagametophyte

Female gametophyte

Archegonia

Egg

Bristlecone pineMale cone

Female cone

Pinus longaeva

The oldest aged specimen is 5,600 y

Current year

Last year’s empty sporangia

Sections you need to have read

17.8 and Introduction to Chapter 31

Courses that deal with this topic

ESC 200 Trees in Our Environment

ESC 221 Dendrology and Autecology