Rare Plant Profile – Soapweed, Yucca glauca Nuttall [1]
Soapweed (Yucca glauca Nuttall) is a long-lived perennial plant, in the Agave Family. Soapweed is so named because its roots contain a high concentration of lathering substances called saponins. When crushed and mixed in water, the saponins produce a lather that can be used as a soap or a shampoo [2].
In Canada, soapweed is found only in Alberta and Saskatchewan [3]. At the northern extent of its range, soapweed naturally occurs in two locations in the southeast corner of Alberta in the Milk River basin [4]. One occurrence is located along the Lost River, a tributary into Milk River. The other occurrence is located along the Milk River coulee slopes in the Pinhorn Grazing Reserve (near the Hamlet of Manyberries). Soapweed grows as either a single rosette of long, narrow, egg- to spear-shaped leaves or as a cluster of rosettes. Fifteen to seventy-five large white flowers are produced on a long stalk that grows from the center of the rosette.
Soapweed has a conservation status rank of S1, or Critically Imperiled, in Alberta and is listed as Endangered [5] on the Alberta Wildlife Act Regulations and as Threatened under the federal Species at Risk Act [6]. This is due to the limited number of occurrences and its mutual and co-dependent relationship with three endangered species of moths, the Yucca Moth (Tegeticula yuccasella), the Non-pollinating Yucca Moth (T. corruptrix), and the Five-spotted Bogus Yucca Moth (Prodoxus quinquepunctellus). As the only host for these moths, soapweed has a unique obligate, mutualistic relationship with its only pollinator, the Yucca Moth. Soapweed will only produce seeds if pollinated by the Yucca Moth and the moth larvae will only feed on yucca seeds.
To learn more about rare plants of Alberta, visit the links provided in the footnotes, and stay tuned for the ANPC’s second edition of the Rare Vascular Plants of Alberta book. This is one of many conservation initiatives that ANPC is working on. Please remember to renew your 2021 membership, as ANPC relies on membership dues and donations to support this and other conservation and education initiatives.
(Photos by Dan Johnson)
Figure 2. Yucca glauca Nuttall fruit
Figure 1. Soapweed rosette with flower stalks
Figure 3. Yucca Moth larvae
Do you know of soapweed (yucca) sites?
The University of Lethbridge is conducting a biogeography study of where Yucca (commonly known as soapweed), and Yucca Moth, the pollinators, are found in Canada. We have surveyed and mapped this plant in the past, and we now request your help to update the database of locations of Yucca plants, whether they bear pods after flowering, and what years pods were formed. This plant is an interesting and durable member of plantings, easily recognized, and long-lived. Mapping their approximate locations and whether they form pods will tell us if the associated special pollinator is doing well, or even expanding its range.
Any answers or partial answers wold be useful to us. We can provide you a report.
- Have you seen, planted, or found Yucca plants? If you answered yes:
- What is the approximate location of this plant (town or general site)?
- About how many Yucca plants are present in this location?
- Have these plants flowered in the past?
- Have these plants produced pods, and what years, if known?
- Would you like to be named as a data contributor in a report?
THANKS! Please send survey responses to: yucca@uleth.ca
Calvin Cooley (Environmental Science student Univ. Lethbridge): calvincooley5@gmail.com
Dan Johnson: dan.johnson@uleth.ca
(Professor) Dept. of Geography and Environment
University of Lethbridge, 4401 University Drive, Lethbridge, AB, T1K 3M4
References:
[1] https://data.canadensys.net/vascan/name/Yucca%20angustifolia
[2] https://www.fs.fed.us/wildflowers/plant-of-the-week/yucca_glauca.shtml
[4] https://open.alberta.ca/publications/0778514927
[5] https://www.qp.alberta.ca/documents/Regs/1997_143.pdf
[6] https://species-registry.canada.ca/index-en.html#/species/265-197
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