Lab 6

Gymnosperms

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

– 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

Gymnosperms

Cycas revoluta Ginko biloba

Ephedra.

Welwitschia mirabilis.

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 downSago palmCycas revoluta

Phylum Cycadophyta

– 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

Cycas revoluta pollen cone

Cycas circinnalis seed coneseed cone openedCycas circinnalis pollen cone

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 Welwitschia mirabilis

Ephedra sinica

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

Gingko biloba

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)

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.

Phylum Coniferophyta: the Conifers

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.

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.

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.

The Conifers

Pollen Cones

• 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

Male Pine Cone

microspores(pollen)

microsporangium

microsporophyll

microsporangium

Pine pollen cone - microsporophyll & a microsporangium (containing microsporocytes).

Microsporangium containing microspores(pollen)

Pine pollen with male gametophyte Germinating pine pollen

air bladder

generative cell(becomes 2 sperm)

tube cell

microsporophyll

Microsporangium With pollen grains

Pine pollen with wings

air cells

Seed cones

sterile bract

megasporophyll

• 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

Seed cones

Pine seed cone with ovulate scale (megasporophyll) and ovule

ovules

megasporophyll

bract

mega-spore

integument

Developing ovulate scale (megasporophyll) in a young pine seed cone

megasporophyll

bract

Future ovule

Archegonia in pine ovule with egg nucleus

2 Archegonia (developed from the megaspore) within the ovule

female gametophyte

egg nuclei

Female Pine Cone Male Pine Cone

microspore(pollen)

microsporan-gium

microsporophyll

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 Strobus with one vascular bundle

Vascular bundle

Subgenus Pinus with two vascular bundles

Vascular bundles

Cross Section of a Pine Leaf