Taxaceae

Taxaceae: Life History and Ecology

The distribution of the Taxaceae is very wide. Taxus is the common name for the Yews, widely distributed throughout the northern Temperate zones of the Old and New Worlds. The Torreya has a distribution in California, Florida, and East China. Pseudotaxus occurs in a small region of East China. Austrotaxus is restricted to New Caledonia.

Taxaceae can sometimes lead to fungus growth, though quite uncommon. The exception is Sphaerulina Taxi which caused Yew Leaf Scorch. Insect pests attack the terminal leaves resulting in bunched leaves, which are harmless but unsightly. The buds can become infected, enlarged and discolored. Mites will then inhabit the center of the buds.

Owls use Yew trees as vantage points over the forest floor. Deer, elk, and moose often like to browse Yew foliage. Birds and small mammals are induced by the berry-like arils since they are attractive and inticing.

Life History of Taxaceae

Taxaceae has some unique reproductive cycles. For example, the Taxus is dioecious but there are occasionally monoecious specimens that have been known to occur. The male cones are found on the underside of branches, found in clusters of four or more. The female cones are found on the underside of branches also, but are pointed and less abundant. Torreya and Amentotaxus have dorsal and ventral scale-like male organs with four abaxial pollen sacs, thus differing from Taxus. The male gametes are very unequal in size.

Pollination is an important part of the life cycle of Taxaceae. Yews are wind pollinated. Female cones develop into fleshy, berry-like bodies called arils. Pollination involves a drop-like mechanism and occurs at the time of meiosis in the ovule. Pollen grains contain just a single nucleus when they are shed.

The nature of the seeds can vary within Taxaceae. In Taxus they are dispersed by birds, who are attracted to them because of the fleshy arils, which contain the seeds.

Sources

Hora, Bayard. The Oxford Encyclopedia of Trees of the World. Oxford University Press: Oxford, New York, Toronto, Melbourne, 1991.

Johnson, Hugh. International Book of Trees - A Guide and Tribute to the Trees of Our Forests and Gardens.. Mitchell Beazley Publishers Limited: New York, 1973.

USDA Forest Service. Pacific Yew: Final Environmental Impact Statements. Portland, Oregon, 1992.