Plant Details

Several Yucca plants can be seen along the North Forest Loop Road, the new Rock Pile Lead trail, and elsewhere on the Arboretum. These plants are known as Adam’s Needle, Bear Grass, or Spanish Bayonet and most likely represent ones that were planted at or escaped from old home sites. They have sword-like pointed leaves (8-32 in. long) that radiate upward from very short woody stems at the ground surface. The margins of these fibrous leaves fray into stiff, filamentous, white threads that curl along the leaf edges. In summer Yucca produces a tall stalk (3-8 ft high) with showy, creamy white flowers. Yucca depends on a moth for pollination, while the moth requires the Yucca as a site for raising its larvae – a classical example of mutualism. The female Yucca moth collects pollen balls from the anthers of a Yucca flower which she then transfers to another flower. At the same time she deposits one or more fertilized eggs into the plant’s ovule. As the moth larva develops, it feeds upon the Yucca seeds.

Yucca belongs to the plant family Agavaceae (though some botanists assign it to the Liliaceae). There are 40-50 members of this genus, many growing in arid desert to semi-desert climates. The UT Herbarium web page lists two species of Yucca present in our area – Yucca filamentosa and Y. flaccida – both commonly called Adam’s Needle. Some botanists consider these both to be Yucca filamentosa. These species were most likely originally found along coastal areas of the Southeast but have become naturalized inland to the west and north.