Plant Highlight: Hesperoyucca whipplei
Hesperoyucca whipplei was originally classified as a Yucca, but was separated out by Baker in 1892. The prefix “hespero” (evening) refers to its occurrence on the west coast of North America, on the side of the continent where the sun sets. It differs from Yucca in its larger and stouter inflorescence, its monocarpic rosettes of leaves (that is, they die after flowering, like Agaves), plus differences in the structure of the flowers and the manner in which the seed pods split open. Despite these distinctions, the species was placed back into Yucca during most of the 20th century, so that it is most commonly found labeled as Yucca whipplei. Recent genetic studies have definitively established its distinctiveness and shown that it is related to Hesperaloe as well as to Yucca, so it is now accepted as a separate genus. The flowers, however, look very Yucca-like. They are white, and often have purple tips (though our flowering specimen does not display this character). The common name for these plants is “Our Lord’s Candle” in reference to its plumes of white flowers, which are especially dramatic when lit by the rising or setting sun.
The range of H. whipplei extends from the mountains of California’s Coast Range east of Carmel in Monterey County down to central Baja California, with eastern outliers in the lower Grand Canyon in Arizona and in the Mexican state of Sonora. Over this range the plants vary considerably. They range in color from green to silvery-blue (like our plants), and in size from heads a foot across to large specimens five feet in diameter (ours are on the large side). In some populations the plants are single, while in others they produce offsets to form a cluster. This led to the naming of separate subspecies, but since there are some populations with both types it seems sensible to recognize only a single variable species. The Baja California form is small, clustering, and frequently has purple tips on the leaves, as well as prominent purple coloring on the tips of the petals. This form was once known as Yucca peninsularis, or later as Yucca whipplei ssp. eremica, but it too may lack enough distinctive characters to warrant a separate name. Our plants resemble the forms encountered at the north end of the range of the species, although they were acquired without locality data. Other specimens have flowered and died in the garden in past years as they reached maturity. These plants are attractive garden subjects and perform very well in Mediterranean climates.