An Illustrated Guide to ARIZONA WEEDS

The University of Arizona Press

WESTERN BRACKEN, bracken, bracken fern, brake fern, eagle fern


FERN FAMILY-Polypodiaceae

WESTERN BRACKEN-Pteridium aquilinum (L.) Kuhn var.pubescens Underw.

DESCRIPTION-A perennial fern which reproduces by spores and widely creeping, branching underground stems, sometimes forming colonies. The large compound leaves (fronds) are 1 to 4 feet high, and 1/2 to 1 l/2 feet long. The leaf stalk, usually mistaken for the stem, actually is attached to the rhizome under the ground.

The triangular deciduous leaves turn brown and die at fall frost, and the new ones arise each spring from the rhizomes. The leaf is divided into numerous segments (leaflets), each of which may be again divided or redivided, with the lowest segments three times compound. The clusters of spore cases densely line the inrolled edges of the underside of the leaves; the spores mature usually in July and August.

DISTRIBUTION-Western bracken, a native and our only weedy fern, grows in the mountains in Arizona. It is very common in shade or partial sun in open yellow pine forests, less common in aspen and spruce; it is also found along the tree edges of mountain meadows, and on steep slopes at higher elevations. It comes in quickly on forestlands which have been burned or logged. In Apache, Navajo, and Coconino counties, southward to Cochise and Pima counties at 5,000 to 8,500 feet elevation.

POISONOUS PROPERTIES-In early spring the young unrolled leaves and tender leaf stalks may be cooked as a vegetable. When mature and tough, they are poisonous to horses and cattle. Sheep have been poisoned experimentally, but natural poisoning is unknown in the United States, and goats are immune. The rhizomes are five times more toxic than the leaves, but are seldom eaten.

The poison is cumulative over a period of about 1 month for horses, and 1 to 4 months for cattle before symptoms appear. Horses usually are poisoned by eating large amounts of hay containing over 20% of dry bracken. Cattle are poisoned by an amount of green or dried leaves about equal to the animal's weight. Livestock, however, seldom eat western bracken on the range when other forage is available.

Copyright (c) 1972 The Arizona Board of Regents

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