Tree Yuccas and Their Ilk

Gunilla and Michel Hamaoui, who live in Woodland Hills, sent me a photo of a tree whose identity they did not know. They also wanted to know how often it flowered.
I did not know what kind of tree this was, so I went to This website allows you to upload photos to a “Plant Identification” forum. Within an hour or so, you usually have a conclusive identity of the plant in question.
This plant is Yucca filifera, a species simply known as tree yucca. It’s an astonishing tree since its growth resembles that of a palm except for a telltale clump of lanceolate or spear-shaped yucca foliage at the top.
The etymology of yucca is misleading since the word is derived from yuca, a Tahitian word for cassava, also known as tapioca, whose edible tuber resembles yams and sweet potatoes and is a staple in the diet of half a billion people worldwide.
Yucca foliage has only a vague resemblance to that of cassava, although cassava plants may grow up to 20 feet tall and their arboreal form, like that of tree yucca, is leafless until reaching the top of their trunks.
Tree yucca grows up to 60 feet tall, which is nearly twice the height of any other yucca — of which there are 40 species — including the Joshua tree (Yucca brevifolia). Branching may not occur until trees are as tall as 30 feet.
Tree yucca is native to central Mexico and somewhat cold sensitive. It flowers between July and August.
Yuccas are slow-growing and may take up to 20 years or longer to flower.
Even after they bloom, an annual floral display is not guaranteed. Flower bud development will be inhibited by moist soil, so you should not water a yucca tree more than once a month, if even that much.
Depending on the species, cold winters also may be hazardous to proper growth of yucca buds and blooms.
One of the most fascinating symbiotic relationships in nature involves yucca moths and yucca plants. Yucca moths emerge from their earthbound cocoons in spring or early summer and mate.
In the process of carrying out pollination, females deposit their eggs in the ovaries of yucca flowers. As seeds begin to form in the flower ovaries, the moth eggs hatch and the larvae feed on the developing seeds. However, the larvae only feed on a small number of the seeds in any flower ovary, so plenty of seeds grow to completion.
What is unique about this symbiosis is that the yucca moth is the only pollinator of yucca plants and developing yucca seed is the only food that yucca moth larvae will eat. Thus yucca moths and yucca plants are completely dependent on each other.
Yucca flower petals are edible when cooked or blended into drinks, but their male and female flower parts (stamen and pistil) are toxic.

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