The Evolution Of Angiosperms

Angiosperms first appeared in the fossil record about 135 million years ago. By about 90 million years ago, angiosperms had probably begun to outnumber gymnosperms. Several factors probably led to the success of this new kind of plant. In many angiosperms, seeds germinate and produce mature plants, which in turn produce new seeds, all in one growing season. This is a tremendous advantage over gymnosperms, which often take 10 or more years to reach maturity and produce seeds. Also, the fruits of flowering plants protect seeds and aid in their dispersal. Angiosperms also have a more efficient vascular system and are more likely to be associated with mycorrhizae than gym-nosperms are. Angiosperms also may gain an advantage by using animal pollination rather than the less-efficient wind pollination method used by gymnosperms. However, wind pollination is used by many successful angiosperms, including many deciduous trees. Finally, angiosperms are more diverse than gym-nosperms, so they occupy more niches, such as in aquatic, epiphytic, and parasitic environments.

figure 28-17

The stinking-corpse lily, Rafflesia arnoldii, has the world's largest flowers but no leaves or stems. The flowers can be male or female, and they are pollinated by flies. The plant lacks chlorophyll and is parasitic on a woody vine native to Southeast Asia.

figure 28-17

The stinking-corpse lily, Rafflesia arnoldii, has the world's largest flowers but no leaves or stems. The flowers can be male or female, and they are pollinated by flies. The plant lacks chlorophyll and is parasitic on a woody vine native to Southeast Asia.

TABLE 28-3 Comparing Monocots and Dicots

Plant type Embryos

Leaves

Stems

Monocots One cotyledon

Parallel venation

Scattered vascular bundles

Flower parts

Usually occur in threes

Examples lilies, irises, orchids, palms, tulips, bananas, pineapples, onions, bamboo, coconut, grasses (including wheat, corn, rice, and oats)

Dicots

Two cotyledons Net venation

Radially arranged vascular bundles

Usually occur in fours or fives

Radially arranged vascular bundles m beans, lettuce, oaks, maples, elms, roses, carnations, cactuses, most broad-leaved forest trees

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www.scilinks.org Topic: Monocots/Dicots Keyword: HM60989

Maintained by the National Science Teachers Association

□ IfiieriMtccnnad

www.scilinks.org Topic: Monocots/Dicots Keyword: HM60989

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