Vascular Plants: Trees, Grass, Ferns, Flowering Plants

Vascular plants make up about 80% of all plants. They have special tissues in their stems to move water and nutrients up and down the plant. This allows the plant to grow to a much larger size. They are also characterized by their reproductive phase. In vascular plants, the sporophyte generation is dominant.

Vascular plants are broken down into three groups:

1) Seedless vascular plants - ferns, horsetails and clubmosses.

2) Naked seed vascular plants - the conifers.

3) Protected seed vascular plants - flowering plants, grasses and deciduous trees.

1) Seedless Vascular Plants - Ferns, Horsetails and Clubmosses

     The sporophyte (diploid 2n) generation dominates and is separate from the gametophyte.
     The gametophyte makes the sperm that travels in water to reach the egg. A new plant results.

Ferns have rhizome stems that run along or under the ground with hair-like roots anchoring them. The leaves or fronds grow directly off the rhizome. New leaves form in curled fiddleheads that uncurl as they grow. The fronds have leaflets that are sometimes divided two or three times.

Name the Ferns and Clubmosses in the activity below.

2) Naked Seed Vascular Plants - Conifers, Cycads, Ginkos

     Also called gymnosperms.
     Gymnosperm seeds are not completely covered by the parent plant when they are formed. They are inside dangling cones.

There are more than 500 species of conifers: pines, spruce, firs, redwoods and cedars.

Physical Traits: The conifers can grow into massive, long-lived trees. They have needle-like leaves that are well adapted to temperature and moisture extremes and high winds. Woody gymnosperms are called softwood trees. In conifers, the tree is the sporophyte generation (diploid 2n). The gametophyte generation is too small to see.

Reproduction: The small male cones are found at the tip of the lower branches. Each scale has two or more micro-sporangia underneath which, through meiotic divisions, produce many winged pollen grains. Millions are release for wind dispersal. The female cones are larger and located near the top of the tree. Each scale in the pinecone has 2 ovules. The pollen grains are blown onto the female cones. This is pollination, getting pollen from makes cone to female cone.  After pollination, each pollen grain develops a pollen tube that grows toward the ovule. When it reaches the ovule, the pollen grain releases its sperm and fertilization occurs. Fertilization is separate from pollination and can take up to 15 months to be completed. Then the fertilized ovule develops into the seed. The seed contains the embryo, food and seed coat. Finally, and almost three years from the release of pollen, the woody female cone opens and releases its seeds. The seeds have papery wings, which help them disperse. If they find a suitable spot and germinate into a seedling, the life cycle has been completed.

Males and female cones have haploid (n) spores. Male cones release pollen in the spring, which is spread by the wind. Some reach female cones, which release a sticky fluid that traps the blowing pollen. The pollen, over time, will burrow into the female cones ovule to reach and fertilize the egg. Eventually the cone will fall and in the right conditions grow into a conifer seedling and then tree.

Study the Gymnosperm Life Cycle below:

3) Protected Seed Vascular Plants  - Flowering (Herbaceous) Plants, Grasses and Deciduous Trees

      They are also called angiosperms. Their seeds are protected inside a fruit.
      There are thought to be more than 235,000 species of angiosperms.

Physical Traits: Angiosperms can be the tiniest pondweed to most giant sugar maple tree. Their powerful vascular tissue allows them to grow quite large with xylem tissue bringing water and minerals from deep in the ground to branches sometimes eighty feet in the air. Woody angiosperms are called hardwood trees.

They have two important traits which make them different from gymnosperms and perhaps more successful in their own niche. They have flowers, inside which are the sexual organs, both male and female. The flower attracts pollinators like insects, bats and birds. Once pollinated, it develops seeds inside some form of fruit. The fruit can be fleshy, dry or highly adapted for dispersal.

Angiosperms can be divided into two classes - monocots and dicots.
The monocots are herbaceous plants with:

• flower parts divided into 3 parts
• parallel leaf veins
• scattered vascular bundles in the stem
• one cotyledon (seed leaf)

These include lilies, palms corn, rice, etc.

The dicots are herbaceous or woody plants with:

• flower parts divided into 4 and 5 parts
• a net leaf vein pattern
• vascular bundles arranged in a circle in the stem
• 2 cotyledons (seed leaves)

These include the maples, mustards, peas, cactus, buttercups, pinks and rose families (common fruits).

Study the Angiosperm Life Cycle below:

Flowering Plant Reproduction:
Flower can take many different forms and can be very simple or very complex. In general, they are made up of rings of leaf-like structures that sit on a receptacle.

The first ring is made up of the sepals, which are often green and cover and protect the flower before it blooms.

Inside the sepals, the next ring is made up of petals. They are usually large, colorful and showy to attract pollinators.

Then comes a ring of stamen - the male part of the flower that produces pollen.

Each stamen is made up of a long, thin filament topped with a pollen-covered anther. It is in the anther where the microspores develop into pollen grains. The pollen is then transport by wind or animal pollinators to the female parts of the flower (or other flowers).

The stamens generally encircle the female part of the flower - the pistil. The pistil has 3 parts.

The stigma is the sticky tip where pollen grains stick.

The ovary is at the base of the pistil and contains the ovules.

The style is the thin stalk that connects the stigma down to the ovary.

After the pollen grains land on the stigma, they grow pollen tubes down the style into the ovule. They each release two sperm into the ovule. One fertilizes the egg and the other fuses with other the divided polar nuclei to form the food for the developing seed, called endosperm.

This double fertilization allows flowering plants to produce seed that contain the embryo, food and a protective seed coat. The wall of the ovary then develops into a fruit that surrounds the seeds - the so-called covered seeds of the angiosperm. The fruit protects the seeds and attracts animals that will carry the seeds away to grow elsewhere (seed dispersal).

Plant Reproduction - A General Explanation
Plant life cycles are more complex than animal life cycles. In animals, we get half our hereditary material (genes) from our mother and half from our father. The one-cell egg and one-cell sperm each contain half, so are said to be haploid. It isnt until the egg is fertilized by the sperm that it becomes diploid - containing a whole set of genetic information.

Plants have both a haploid and diploid phase of reproduction, which are both multi-cellular. In the life cycle of a plant, they go back and forth between these two phases. This is called alternation of generations. The two phases of reproduction are called the sporophyte and the gametophyte.

• In nonvascular plants (mosses) the gametophyte generation is the phase we see as the plant in the forest.
• In vascular plants (flowering plants and conifers) the sporophyte generation is the phase we see.

Vascular plants are adapted for life on dry land with seeds protected from drying out by a seed coat. They also have ways to collect water (roots) and food (leaves) and move it through the plant (xylem and phloem).

The gametophyte generation forms the gametes (sperm and egg) that are haploid (n) (with only half the genetic material). During fertilization (pollination), they fuse together and form a diploid (2n) plant with its full compliment of genes. This is the sporophyte generation. Summary: The gametophyte generation is haploid and the sporophyte generation is diploid.