Gymnosperms nakedseed Four major living groups. Cycads (Cycadophyta), Welwitschia group (Gnetophyta), Ginkgo, the Maiden Hair Tree (Ginkgophyta), and the.
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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)
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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
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
Cedrus deodora
Male cones – all lined up and ready to go!
The diminutive female cone
Developing seed cones
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
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