Flowering Plants (Angiosperms)

Angiosperms or flowering plants are “protected seed vascular plants” because their seeds are protected inside a fruit. They include herbaceous plants, grasses and deciduous or hardwood trees. 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).

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. 1) The first ring is made up of thesepals , which are often green and cover and protect the flower before it blooms. 2) Inside the sepals, the next ring is made up of petals. They are usually large, colorful and showy to attract pollinators. 3) Then comes a ring ofstamen - 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). 4) The stamens generally encircle the female part of the flower - thepistil . The pistil has 3 parts. • Thestigma is the sticky tip where pollen grains stick. • Theovary is at the base of the pistil and contains the ovules. • Thestyle 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 theovule . 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 calledalternation 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.