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Lab 6 Gymnosperms
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Gymnosperms seed bearing plants – but “naked seeds”
often borne on cones do not produce flowers - angiosperms Gymnosperms -reduced male gametophyte (development of pollen grains) -internal fertilization -reduced female gametophyte (development of ovules) -naked seeds -advanced vascular tissue comprised of tracheids -woody -perennial Angiosperms -reduced male gametophyte (development of pollen grains) -internal fertilization -reduced female gametophyte (development of ovules & an embryo sac) -seeds – borne in fruits -development of flowers -advanced vascular tissue with tracheids and vessel elements -herbaceous and woody -annuals and perennials
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Gymnosperms Phylum Ginkgophyta - ginkos
only one species left – Ginkgo biloba deciduous leaves - fanlike formation tolerates air pollution well trees bear fleshy seeds that smell rancid Phylum Coniferophyta – largest group “cone-bearing” 600 species of conifers many are large trees most are evergreens – retain their leaves throughout the year Cycas revoluta Ginko biloba Welwitschia mirabilis. Ephedra.
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Phylum Cycadophyta found in subtropical and tropical regions
often confused with young palms stout trunk with compound leaves most are less than 2m tall Macrozamia = 18m tall 9 to 10 genera – ~300 species total ~25% are considered endangered take a very long time to grow stout, cylindrical trunk that does not branch leaves are pinnate (“feathers” on a bird) are grow directly from the trunk central leaf stalk with parallel “ribs” emerging from the sides leaves grow from the top of the crown down Phylum Cycadophyta Sago palm Cycas revoluta
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Phylum Cycadophyta require very specific pollinators – usually beetles
produce seed and pollen cones on separate plants = dioeicious pollen cones are spirally arranged microsporophylls that bear clusters of microsporangia pollen cone can be very large seed cones are variable in morphology variety in number and shapes require very specific pollinators – usually beetles seeds contain neurotoxins and should not be eaten Phylum Cycadophyta Cycas revoluta pollen cone seed cone opened Cycas circinnalis seed cone Cycas circinnalis pollen cone
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Phylum Gnetophyta 3 genera of gymnosperms:
1. Gnetum - are mostly vines or shrubs with very broad leaves 30 species native to southeast Asia, tropical Africa and the Amazon basin seeds are eaten 2. Ephedra – shrubs and bushes 40 species inhabit desert regions in northern Mexico and southwestern US reduced scale-like leaves used in the production of ephedrine 3. Welwitschia – only one species Welwitschia mirabilis deserts of South Africa leaves grow perennially – becoming increasingly longer largest leaves in the plant kingdom Ephedra sinica Welwitschia mirabilis
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Phylum Gingkophyta contains a single living species – Gingko biloba
“living fossil” also known as the “maidenhair tree” woody tree broad leaves – very distinct shape trees are dioecious microsporangiate trees megasporangiate trees no ovulate cones- ovules occur in pairs at the ends of a short stalked megasporophyll – unprotected at maturity when the female tree produces its seeds – contain butyric acid which has a putrid odor Phylum Gingkophyta Gingko biloba
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Phylum Coniferophyta 575 species
pine trees, firs, spruces, hemlocks, redwoods, cedars 290 million years old largest genus – Pinus over 100 living species predominant in the northern hemisphere also planted in the southern hemisphere – only the Merkus pine occurs there naturally world’s oldest known living organism – bristle cone pine (4,600 years old)
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Phylum Coniferophyta: the Conifers
Douglas fir. “Doug fir” (Pseudotsuga menziesii) provides more timber than any other North American tree species. Some uses include house framing, plywood, pulpwood for paper, railroad ties, and boxes and crates.
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Pacific yew. The bark of Pacific yew (Taxa brevifolia) is a source of taxol, a compound used to treat women with ovarian cancer. The leaves of a European yew species produce a similar compound, which can be harvested without destroying the plants. Pharmaceutical companies are now refining techniques for synthesizing drugs with taxol-like properties.
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Bristlecone pine. This species (Pinus longaeva), which is found in the White Mountains of California, includes some of the oldest living organisms, reaching ages of more than 4,600 years. One tree (not shown here) is called Methuselah because it may be the world’s oldest living tree. In order to protect the tree, scientists keep its location a secret.
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Sequoia. This giant sequoia (Sequoiadendron giganteum), in California’s Sequoia National Park weighs about 2,500 metric tons, equivalent to about 40,000 people. Giant sequoias are the largest living organisms and also some of the most ancient, with some estimated to be between 1,800 and 2,700 years old. Their cousins, the coast redwoods (Sequoia sempervirens), grow to heights of more than 110 meters (taller than the Statue of Liberty) and are found only in a narrow coastal strip of northern California.
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The Conifers
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Pollen Cones Male Pine Cone considered to be simple cones
microspores (pollen) microsporangium microsporophyll considered to be simple cones one single cone axis bearing modified leaves known as microsporophylls cones typically occur in clusters near the ends of branches pollen is liberated to the wind and blown away pollen has one cell and two large air bladders that increase its buoyancy in air wind dispersal is inefficient – so few pollen grains actually land on the ovulate cone but conifer forests are very dense
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Microsporangium containing microspores (pollen)
Pine pollen cone - microsporophyll & a microsporangium (containing microsporocytes). Microsporangium containing microspores (pollen) Microsporangium With pollen grains microsporophyll Pine pollen with male gametophyte Germinating pine pollen air bladder generative cell (becomes 2 sperm) tube cell
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Pine pollen with wings air cells
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Seed cones more complex than pollen cones compound cone
each consists of a cone axis with scales the scales bear leaves that are called sterile bracts in addition to sporophylls scale is a fused megasporophyll with two ovules megasporophyll also called an ovulate scale sterile bract megasporophyll
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Seed cones megasporophyll ovules integument bract
Pine seed cone with ovulate scale (megasporophyll) and ovule ovules megasporophyll bract mega- spore integument
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Developing ovulate scale (megasporophyll) in a young pine seed cone
bract Future ovule 2 Archegonia (developed from the megaspore) within the ovule female gametophyte egg nuclei Archegonia in pine ovule with egg nucleus
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Female Pine Cone Male Pine Cone microsporophyll microsporan- gium
microspore (pollen) microsporan- gium microsporophyll Female Pine Cone
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The Pinus genus is divided into two subgenera that are separated by the presence of either one vascular bundle in the leaf (subgenus Strobus) or two (subgenus Pinus). Subgenus Pinus with two vascular bundles Vascular bundles Vascular bundle Subgenus Strobus with one vascular bundle
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Cross Section of a Pine Leaf
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