Conifer

Conifer

Resources

Conifer (common name for phylum Pinophyta) is a type of tree that thrives in temperate and boreal climates. Characterized by seed-bearing cones, conifers typically have narrow, needle-like leaves covered with a waxy cuticle and straight trunks with horizontal branches. These trees are usually evergreen, meaning they do not shed their leaves all at once, and can photosynthesize continually. There are two orders of conifer, Pinales and Taxales.

There are two major seed-producing plants: gymnosperms (meaning “naked seed”) and angiosperms (meaning “enclosed seed”). These two groups get their names from their female reproductive characteristics: the gymnosperms have egg cells or seeds on the scales of the cone, while the angiosperm seeds are enclosed within ovaries, which, if fertilized, eventually turn into fruit. Conifers are one of the three groups of gymnosperms, which also include the cycads (tropical plants with palmlike leaves) and a group consisting of four plants having both gymnosperm and angiosperm features.

Male and female cones grow separately on the same tree. The female cones are larger and grow on the upper branches, while the male cones tend to grow on the lower branches. Both female and male cones have a central shaft with scales or leaflike projections called sporophylls that are specially shaped to bear sporangia (a reproductive unit). Each female sporophyll has an area where two ovules (each containing a group of fertile eggs) develop within a protective tissue called the nucellus. Male sporangia contain thousands of microspores, which divide (through meiosis) into more microspores, which eventually turn into grains of yellow pollen. Pollen dispersal depends on air currents, and with dry, windy conditions, a grain of pollen can travel miles from where it was released. The pollen enters the female cone through an opening in the nucellus and sticks to the ovule. After fertilization, a little conifer seedling, complete with a root, develops within a seed coat. The seed is still attached to the scale of the cone, which, when caught by the wind, acts as a wing to carry the seed.

Some conifers can be shrub-like, while others, like the giant sequoia (Sequoia sempervirens ), grow very tall. Through fossils, it has been learned that conifers have existed since the Carboniferous period some 300 million years ago. Most species no longer exist. Currently there are approximately 550 known species. In North America, firs (Abies ), larches (Larix ), spruces (Picea ), pines (Pinus ), hemlocks (Tsuga ), and junipers (Juniperus ) are most common in mountain ranges of the Pacific Northwest and the Rocky Mountains. Conifers also extend through the northern regions of the United States and Canada, as well as into mountain ranges closer to the tropics. Some pine species grow in lowland areas of the southeastern United States.

Conifers are an important renewable resource; they provide the majority of wood for building, as well as pulp for paper. Resins, oleoresins, and gums are important materials for the chemical industry in products such as soaps, hard resins, varnishes, and turpentine.

See also Juniper; Spruce; Yew.

Resources

BOOKS

Wilkins, Malcolm. Plantwatching. New York: Facts On File, 1988.

PERIODICALS

Chaw, S. M., et al. “Seed Plant Phylogeny Inferred From All Three Plant genomes: Monophyly of Extant Gymnosperms and Origin of Gnetales from Conifers.” Proceedings of the National Academy of Sciences of the United States of America 97 (2000): 4086-4091.

OTHER

American Conifer Society. “American Conifer Society” <http://www.conifersociety.org> (accessed November 20, 2006).

Christine Miner Minderovic