Soapweed (Yucca glauca)

Description
Soapweed

Size

  • Can grow up to one metre (3.28 feet) in height from the base

Flowers

  • Bell-shaped; usually found growing from stalks in drooping clusters of 25 to 30
  • Leathery, oval-shaped petals are cream to greenish-white in colour
  • Length up to five centimetres (1.97 inches)
  • Six stamens (male reproductive stalks that hold the pollen) stand from the centre of each flower

Fruit

  • Oblong, cream coloured capsules
  • Length about five to seven centimetres (1.97 to 2.75 inches)

Leaves

  • Leaves are long and thin and radiate from the base of the stem
  • Can grow up to 60 centimetres (23.6 inches) long
  • Are sharp and hard at the tip
  • Are green in colour with frayed whitish margins
Distribution
  • Soapweed grows in only two locations in southern Alberta, both locations in the Milk River region just north of the Canada/United States Border
  • While soapweed is at the northernmost limits of its range in Canada, it is widely distributed in the western United States.
Natural History

Habitat

  • Commonly found on dry, eroded and exposed slopes with sparse vegetation
  • Prefers well-drained, sandy or gravelly soil

When Active

  • Is perennial, living for two or more years, and flowering and fruiting several times during its lifespan
  • Flowers from May to July in Alberta
  • Flowers are open during the evening, and almost closed on bright, sunny days
Reproduction and Growth

The reproductive cycle of soapweed depends exclusively upon the lifecycle of its pollinator, the yucca moth. See:

  • Adult female yucca moths actively collect pollen from one soapweed plant, then usually fly to another. Upon finding a fresh flower, a female first inserts her ovipositor through the carpel wall and lays an egg next to the developing ovules.
  • She then climbs to the tip of the style, and using her maxillary tentacles (appendages unique to yucca moths), she actively transfers pollen into the stylar canal, pollinating the plant.
  • There is no other consistently successful mechanism of pollen transfer, and yucca moth larvae feed only on yucca seeds.
Conservation and Management

Status

Soapweed is classified as At Risk in the General Status of Alberta Wild Species report. See:

Soapweed is currently listed as Endangered under the Wildlife Act. For more information on this species and the assessment and listing process, see:

For more information on this species, see the Status of Soapweed in Alberta report at:

Issues

  • The success of Alberta soapweed populations is heavily dependant upon the success of yucca moth populations. Along with the soapweed, the yucca moth has also been recommended for listing as Endangered under the Wildlife Act.
  • Other factors limiting the success of soapweed populations include:
    • Habitat fragmentation due to agricultural activity
    • Reduction of plants due to high winds or cattle and wild ungulate grazing
    • Harvesting of soapweed for human horticultural and medicinal uses

Current Management

A joint recovery plan for soapweed and yucca moth has been was developed and is under implementation. For details, see:

Research is ongoing in Alberta regarding soapweed and yucca moth interaction to better understand the mutual relationship and establish appropriate management measures.

 

Page Information

Updated: Mar 4, 2014