How Do Gymnosperm Seeds Differ From Angiosperm Seeds?

Gymnosperms

• Gymnosperm plants most resemble those of prehistoric times and are so called because they are characterized by naked (gymnos) seeds (sperm). Seeds are held within scaly tissues often called cones. Gymnosperm plant classes, or phyla, include cycads, ginko, gnetophytes and conifers. Fossils confirm their existence in the Paleozoic era, an evolutionary step away from ferns and one preceding angiosperms. Cycads, one of the phyla, strongly resemble ferns in appearance, and the needles and cones of conifers began their development before that of flowering and fruiting plants. Cycads and ginko are dioecious, that is, plants are strictly male or female. Some conifers are monoecious, with male and female cone formations on the same plant.

Angiosperms

• Angiosperms date back to the Mesozoic era, developing in abundance during the Jurassic and Cretaceaous periods as gymnosperms began to decline in numbers. Angiosperm seeds were contained within a fruit, and reproduction depended upon pollination of a flower, which then developed into seed-holding fruit. Angiosperms can have both male and female organs on the same plant but still depend on outside sources of fertilization like wind or animals. Some plants are dioecious, only male or only female. The classic plant cited is holly; without both male and female plants, there will be no berries.

Reproductive Differences - Gymnosperms

• Wind is the major agent for transferring male pollen grains to female seeds for fertilization. Because seeds are not enclosed within a fruit, pollen grains are deposited directly next to the seeds and form a tube connecting pollen to seed. Fertilized seeds are then dispersed by wind or gravity, as the scaly cones or seed wrappers deteriorate. Periods of dormancy vary. Perhaps the best known, and most dramatic, of gymnosperm reproductive cycles is that of the bristle-cone pine. Cones open to release seeds only in the presence of intense heat; forest fire is the most common agent for increasing the bristle-cone population.

Reproductive Differences - Angiosperms

• Angiosperm seeds are characterized by greater variety in size and appearance than gymnosperm seeds. They are contained in a wide variety of fruits ranging from a swelling on a flower stem to apples and zucchini. Seeds are dispersed by wind, gravity and a number of animal agents including humans. Some seeds depend on ingestion and excretion by birds or animals to soften seed coatings enough to permit sprouting into new plants. Pollination of angiosperms can be accomplished by wind or by insects that visit plant flowers. Many angiosperm plants rely on honey bees, which are estimated to fertilize 90% of the world's food crops. Other insects may have special focus on only one or two kinds of plants. Flowers may be designed to attract a wide or narrow variety of pollinators.