Yucca angustissima and Yucca harrimaniae are so similar that there is significant disagreement among experts about exactly what distinguishes one species from the other. Some experts even disagree with themselves! One expert indicated in several editions of his flora that Y. angustissima is not found in southwest Colorado; in a later edition, he indicates that both species are found there. The Flora of North America indicates that Y. angustissima is not found in southwest Colorado. My observations are that both species are found in southwest Colorado, southeast Utah, and northeast Arizona. There may be few to no occurrences of Y. harrimaniae in northwest New Mexico. See the BONAP range maps below. After I compared many descriptions of the two species, I found what appears to be several agreed upon characteristics that separate the two species. The first two characteristics below seem to be the most consistent for identification. The flower stalk and flower cluster (the peduncle and inflorescence) of Y. angustissima can be 4+ feet tall. Y. harrimaniae peduncle and inflorescence are typically no more than 2 1/2 feet tall. The lowest flowers of Y. angustissima open above the leaf tips; the lowest flowers of Y. harrimaniae open below the leaf tips. The upper side of Y. angustissima leaves tend to be flattened; leaves of Y. harrimaniae tend to be concave. I find that leaf length varies enormously in both species. Some plants have leaves only 6 inches long, whereas other plants have leaves over 20 inches long. Flowers of Y. angustissima generally taper at both ends, somewhat ovoid shaped; those of Y. harrimaniae are broadly bell-shaped. The flowers of Y. angustissima are white to pale green; those of Y. harrimaniae more often have a purple tinge. (I find that when fully developed, the flowers or both species are almost always a creamy white.) Stanley Welsh, Utah plant expert, indicates that the style of Y. angustissima is "white to pale green"; the style of Y. harrimaniae is green. One would think that with this many distinguishing characteristics it would be easy to identify the two plants. It often is not, because these characteristics are variable and, as Welsh points out, the two plants form "apparent intermediates". Pollination is the same for both Y. angustissima and Y. harrimaniae. The flowers of both species are thick, waxy, and attractive, but these characteristics do not bring about normal pollination. Because of the unusual structure of Yucca flowers, they can only be pollinated by having pollen forced onto the stigma. This task is accomplished only by the Tegeticula genus of moth, primarily Tegeticula yuccasella, the Pronuba Moth. The arrow in the photograph to the right points to a Pronuba Moth at work. The usually night flying Pronuba drills a hole in the ovary of the flower, lays eggs, and in the process pollinates the Yucca. The Yucca then becomes food for the larva. The hole can be seen in every Yucca fruit. See the last photograph on this page. Linnaeus named the Yucca genus in 1753. We do not know why he used the Carib word "Yucca" that had been previously applied as a common name for Manihot esculenta, the Manihot Plant or Cassava. Although Manihot and Yucca do have large tuberous roots they otherwise do not resemble each other and in fact are in two different families: Manihot is Euphorbiaceae and Yucca is Asparagaceae. |
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| Yucca angustissima (Narrow Leaf Yucca) Asparagaceae (Asparagus Family) Synonym: Agavaceae (Agave Family) Semi-desert,
foothills. Woodlands, canyons, openings. Spring. Narrow Leaf Yucca is very common in Utah Canyon Country, northern Arizona, western New Mexico, and southwestern Colorado, often replacing the Broad Leaf Yucca as the dominant Yucca. Yucca angustissima leaves are a delicate light green, seven to twenty-four inches long, and, usually, quite narrow. From the center of the leaves a flower stalk emerges in early spring and grows rapidly to about three or four feet (although the stalk can be as much as six feet tall). A long cluster of very handsome somewhat egg-shaped flowers follows. The plant was first collected by John Bigelow in 1854 and famed St. Louis physician and botanist, George Engelmann, named it, probably soon after it was collected, but for some reason did not publish the name. Trelease published the description of this species in 1902 and retained the name that Engelmann had given this species. "Angust" is Latin for "narrow" and "issima" is a Latin suffix indicating the superlative, hence "very narrow" leaves. |
Species present in state and native
Species present in state and exotic
Species not present in state
Species present and not rare
Species present and rare
Species extirpated (historic)
Species extinct
Species noxious
Species exotic and present
Eradicated
Questionable presence
