Division Anthophyta, the angiosperms, or flowering plants, contains 99.5% of all extant plant species, as well as 80% of all living plants. First appearing in the Cretaceous period, angiosperms contain several key adaptations that allowed them to become dominant in the plant world.

First of all, angiosperms typically have broad, flat leaves, which allows for a more efficient collection of solar energy and a better rate of photosynthesis. Also, the vascular tissues of angiosperms have much stronger cell walls than those of gymnosperms. The one most distinguishing feature of flowering plants, however, and the one that most accounts for their evolutionary success, is the flower.

As demonstrated in the diagram, the flower consists of several specialized leaf types on a short stem. The stamen, or the male part of the flower, consists of a short stalk topped by an anther, where pollen is produced. The female part, the carpel, is made up of a sticky stigma, which traps pollen grains, a tube leading down to the ovary, and the ovules, which produce eggs.

In the life cycle of an angiosperm, the anther produces haploid spores, which develop into pollen grains, the male gametophytes. In the ovules, haploid spores develop into the female gametophytes, which produce eggs. During pollination, discussed below, a pollen grain lands on the stigma (unlike in gymnosperms, in which the pollen lands directly in the ovule), and grows a pollen tube down the stem of the carpel and into an ovule, through which sperm are released from the pollen grain. The sperm fertilize the egg in the ovule, creating a diploid zygote.

After fertilization, each ovule grows into a seed with a hard coat, containing a developing embryo and a food supply. The ovary grows fleshy tissue and becomes a fruit, which aids in seed dispersal. After germination, each seed can grow into a new plant.

The methods of pollen dispersal in angiosperms are adaptations that allow them to reproduce more efficiently. In gymnosperms, pollen is dispersed by the wind, which is a very ineffective method, wasting most of the pollen grains. In many angiosperms, the color or scent of the flower itself attracts specific animals to it, and to the nectar, a sugary fluid produced by angiosperms for just this purpose, inside.

While consuming nectar, animals, usually insects, birds, or bats, are dusted with pollen grains. The pollen usually is dropped off in another flower the next time the animal stops for a meal. Thus, many flowering plants have evolved relationships with very specific animals, to ensure that their pollen is distributed only to other plants of the same kind.

Two other reproductive adaptations enhanced the success of the angiosperms. The first is the rapid rate of seed production; unlike in gymnosperms, which often have periods of over a year between pollination and fertilization, most angiosperms cut that period to a few weeks. This enables them to take advantage of short growing seasons in many inhospitable habitats, such as deserts.

The other big advantage of the angiosperms is in seed dispersal. The evolution of the fruit allowed angiosperms to cultivate more relationships with animals: many animals like to eat the fruits, but the hard seed coats pass through animal digestive tracts and exit the animal, with some ready-made fertilizer, a good distance from the original plant. Thus, angiosperms have a very effective method of distributing seed that allow populations of the plants to quickly spread.

There are two classes of angiosperms: the monocots, whose seeds have only one tiny cotyledon, and the far more numerous dicots, whose seeds have two tiny cotyledons.

Procedures:
1. Diagram.
2. Define gymnosperm.
3. Diagram the life cycle of a "pine".
4. Describe conifers.