Chlorogalum pomeridianum

INTRODUCTORY

 
  Image copyright © Lee Dittmann; used with permission.
AUTHORSHIP AND CITATION:
Reeves, Sonja L. 2006. Chlorogalum pomeridianum. In: Fire Effects Information System, [Online]. U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station, Fire Sciences Laboratory (Producer). Available: http://www.fs.fed.us/database/feis/ [].

FEIS ABBREVIATION:
CHLPOM

SYNONYMS:
None

NRCS PLANT CODE [59]:
CHPO3

COMMON NAMES:
soap plant
wavyleaf soap plant
Indian soap plant
Indian soap root
soap root

TAXONOMY:
The scientific name of soap plant is Chlorogalum pomeridianum (DC.) Kunth (Liliaceae) [17,25,31]. Soap plant is 1 of 5 species in the Chlorogalum genus [13] and the most abundant member of the genus [52]. Accepted varieties are [17,25,31]:

Chlorogalum pomeridianum var. pomeridianum (DC.) Kunth
Chlorogalum pomeridianum var. minus Hoover
Chlorogalum pomeridianum var. divaricatum (Lindl.) Hoover

LIFE FORM:
Forb

FEDERAL LEGAL STATUS:
No special status

OTHER STATUS:
None

DISTRIBUTION AND OCCURRENCE

SPECIES: Chlorogalum pomeridianum
GENERAL DISTRIBUTION:
Soap plant is a narrow endemic. Distribution is limited to the southwest corner of Oregon southward into southern California [31]. The Flora of North America  provides a distributional map for soap plant and its varieties.

Populations of Chlorogalum pomeridianum var. divaricatum and C. p. var. minus are documented only in California. Chlorogalum p. var. pomeridianum occurs in California and Oregon [59].

ECOSYSTEMS [19]:
FRES21 Ponderosa pine
FRES28 Western hardwoods
FRES34 Chaparral-mountain shrub
FRES42 Annual grasslands

STATES/PROVINCES: (key to state/province abbreviations)
UNITED STATES

CA OR


BLM PHYSIOGRAPHIC REGIONS [5]:
1 Northern Pacific Border
3 Southern Pacific Border
4 Sierra Mountains

KUCHLER [34] PLANT ASSOCIATIONS:
K010 Ponderosa shrub forest
K026 Oregon oakwoods
K030 California oakwoods
K033 Chaparral
K034 Montane chaparral
K035 Coastal sagebrush
K036 Mosaic of K030 and K035
K048 California steppe

SAF COVER TYPES [15]:
233 Oregon white oak
234 Douglas-fir-tanoak-Pacific madrone
244 Pacific ponderosa pine-Douglas-fir
245 Pacific ponderosa pine
246 California black oak
247 Jeffrey pine
248 Knobcone pine
249 Canyon live oak
250 Blue oak-foothills pine
255 California coast live oak

SRM (RANGELAND) COVER TYPES [50]:
109 Ponderosa pine shrubland
110 Ponderosa pine-grassland
201 Blue oak woodland
202 Coast live oak woodland
204 North coastal shrub
205 Coastal sage shrub
206 Chamise chaparral
207 Scrub oak mixed chaparral
208 Ceanothus mixed chaparral
209 Montane shrubland
214 Coastal prairie
215 Valley grassland

HABITAT TYPES AND PLANT COMMUNITIES:
In addition to the species listed above, other trees commonly associated with soap plant are California bay (Umbellularia californica) and California buckeye (Aesculus californica) [16].

The shrub layer where soap plant occurs is dominated by 1 or more of the following species: wedgeleaf ceanothus (Ceanothus cuneatus), manzanita spp. (Arctostaphylos spp.), eastern Mojave buckwheat (Eriogonum fasciculatum), common snowberry, oceanspray (Holodiscus discolor), cluster rose (Rosa pisocarpa), pale serviceberry (Amelanchier pallida), and poison-oak (Toxicodendron diversilobum) [22,56].

Herbaceous species occurring with soap plant are brome spp. (Bromus spp.), rattail sixweeks grass (Vulpia myuros), ripgut brome (Bromus diandrus), California brome (B. carinatus), western sword fern (Polystichum munitum), yerba buena (Clinopodium douglasii), woodland strawberry (Fragaria vesca),  mountain sweetroot (Osmorhiza berteroi), Pacific blacksnakeroot (Sanicula crassicaulis), American vetch (Vicia americana), Columbian larkspur (Delphinium trolliifolium), licorice fern (Polypodium glycyrrhiza), bigflower tellima (Tellima grandiflora), false carrot (Yabea microcapra), catchweed bedstraw (Galium aparine), Indian pink (Silene californica), cucamonga manroot (Marah macrocarpus), and prettyface (Triteleia ixioides ssp. scabra) [22,56].

Soap plant is not documented as an indicator or a dominant species in vegetation types for California and Oregon. It is most commonly associated with chamise chaparral and oak woodland plant communities [22,56], but is also known to occur in evergreen forests [16]. Vegetation classifications for communities where soap plant is a component species follow:

CA, general:
knobcone pine (Pinus attenuata) communities [61]
purple needlegrass (Nassella pulchra) associations south and east of Monterey [46]
abundant in chamise (Adenostoma fasciculatum) brushlands [24]

Bald Hills oak woodlands, Redwood National Park:
Soap plant showed 0.78% frequency in a Oregon white oak/common snowberry (Quercus garryana/Symphoricarpos albus var. laevigatus) community, and showed 0.83% frequency in the Oregon white oak/orchard grass (Dactylis glomerata) community on mesic, lower concave slopes. It occurred in a mockorange/brittle bladder-fern (Philadelphus lewisii/Cystopteris fragilis) community occurring in a stream channel community with a dense shrub layer, soap plant had 0.50% frequency. Soap plant had 0.75% frequency in a Sierra gooseberry/varileaf phacelia (Ribes roezlii/Phacelia heterophylla) community, a rock outcrop type with a moderately dense shrub layer. Soap plant had 1 to 5% cover in all of these bald hill communities [56].

Pinnacles National Monument: Soap plant occurred in chamise chaparral with 3% mean cover and 16.7% mean frequency [22].

Ring Mountain Preserve, Marin County: Soap plant was frequently encountered in the serpentine bunchgrass community (typified by many boulders strewn among perennial grasses and bulbous plant species), with 9.48% average frequency on north and south slopes and on ridgetops. It had 0.84% frequency in the nonnative annual grassland community. Soap plant had 3.3% cover in the northern coyote bush (Baccharis pilularis) community (characterized by grassland slopes), and had frequency of 6.47% in the freshwater seep community (characterized by the presence of surface water, although some drainages typically dry completely by June) [16].

Santa Ana Mountains: On a knobcone pine serpentine site, soap plant occupied exposed sites with 7% cover, but was not found on surrounding chaparral [60].

BOTANICAL AND ECOLOGICAL CHARACTERISTICS

SPECIES: Chlorogalum pomeridianum

 
  Image copyright © Lee Dittmann; used with permission.
 

GENERAL BOTANICAL CHARACTERISTICS:
The following description of soap plant provides characteristics that may be relevant to fire ecology, and is not meant for identification. Keys for identification are available [25,38,39].

Soap plant is a native, perennial forb. The plant has a basal tuft of wavy, 1-inch (2.5 cm) wide, linear leaves. The leaves are flaccid and stretch along the ground up to 18 inches (46 cm). The liliaceous, star-like flowers of soap plant have 3 sepals and 3 petals and are borne on a leafless, paniculate inflorescence composed of racemose axes. The inflorescence can reach heights up to 6 feet (1.8 m). The flowers are vespertine (opening or blooming in the evening) and ephemeral [11,12,13,27,28,38]. There can be up to 200 flowers per plant [52]. The fruit is a capsule [12]. Soap plant seeds are large and black, numbering 1 or 2 per locule [38]. The bottle-shaped bulb of soap plant is 3 to 6 inches (7-15 cm) long and 1 to 3 inches (3-8 cm) wide. It is densely covered with persistent dark brown fibers [11,12,39]. It is buried at a depth of 4 to 12 inches (10-30 cm). Burial is achieved over several growing seasons, as the bulb has contractile roots that continually pull it downward [29].

RAUNKIAER [43] LIFE FORM:
Geophyte

REGENERATION PROCESSES:
Soap plant regenerates by seed and vegetative means. Natural disturbances like fire and rockslides activate vegetative reproduction from the underground bulb [2]. Vegetative reproduction can also occur when plants are mature, by longitudinal splitting of the bulb. Plants that start out from seed take 5 to 7 years to reach reproductive age [52].

Pollination: There is only a small window of time in which the flowers of soap plant can be pollinated, since the flowers open for only a few hours on only 1 day. They open rapidly in the late afternoon, produce nectar and deliquesce some 6 to 8 hours later, whether pollination takes place or not [27,52]. Large bees (honeybees, carpenter bees, and 2 species of bumblebee) are apparently the only effective pollinators. Rare or infrequent visits are made by yellow jackets, mining bees (Lasioglossum sisymbrii), and Allen's hummingbirds [52]. Sphingid moths are noted to visit the soap plant flowers after dark [28]. Removal of the shrub layer and the subsequent increase in light availability may enhance pollination after fire (see Fire adaptations) [20].

Breeding system: A study by Stockhouse and Wells [52] showed that soap plants are self-compatible; however, this does not mean self-fertilization occurs naturally in the species. It is still dependent upon pollinators to transfer pollen to the stigmatic surface for fertilization to take place in the field [28,52].

Seed production: Flowering and seed production increase after fire, allowing the use of the available mineral seed bed and thereby enhancing soap plant seedling establishment [20]. In California chaparral, most geophytes produce nondormant seeds in the 1st year after fire [7]. Seed is not set in the absence of an animal pollinator [52].

Seed dispersal: The mode of dispersal of the soap plant is autochory, dispersal by the plant itself. Seeds are large, unspecialized for dispersal, and depend on factors such as gravity [32].

Seed banking: Following fire, soap plant emerges as part of the plant community, possibly from a seed supply that has lain dormant since the last fire [35].

Germination: The seeds of soap plant are nonrefractory: germination is not stimulated by high temperatures; instead, the seeds are sensitive to high temperatures  [32,57]. Seeds are immediately germinable typically germinating readily upon wetting, and incubating under moderate temperatures [32]. Experimental findings suggest that soap plant seeds generally germinate approximately 7 days after imbibition [29].  Contradicting evidence produced in experimental laboratory studies showed that seeds of soap plant germinated only after being stratified at 41 ºF (5º C) for 60 days [57].

Seedling establishment/growth: In California chaparral, seedling establishment for most geophytes, like soap plant, takes place in the 2nd postfire year, when light and nutrient levels remain high but shrub competition, herbivory, and seed predation are still low [7]. In order to survive summer drought seedlings must develop rapidly to insure an adequate root system and underground storage organ [32].

Asexual regeneration: Soap plant sprouts after fire from deeply buried bulbs [32]. Bulbs may be dormant for 10 or more years under adverse conditions such as drought, sprouting when conditions are favorable [41].

SITE CHARACTERISTICS:
Soap plant is an abundant forb, common throughout coastal sage scrub, chaparral, and coastal terrace prairies [12,39,52,55]. It occurs on dry, open woodlands and rocky hillsides, bluffs, and grasslands [11,13,25,30,38,39,52]. It most commonly occurs, however, on burned and unburned chaparral [18,24,36,53] on shallow, rocky, serpentine soils [47]. Sweeney [57] adds that soap plant is abundant and widespread on burns and on open and disturbed sites adjacent to burns. Other common occurrences are under dense brush, near edges of brush, and on partly open sites within brush stands. In Pinnacles National Monument, soap plant is found on south-facing slopes that are drier and have typically shallower soils compared to other chaparral communities [22].

The climate in which soap plant thrives is described as mediterranean [47], with cool, wet winters and warm, dry summers [22]. The mean annual precipitation ranges from 16 to 20 inches (410 -510 mm) [46].

The following table provides elevations where soap plant has been collected.

Location Elevation
California below 5,000 feet (1,524 m) [25,38,52]
Elk Creek Drainage (Sequoia National Park) 2,100 feet (640 m) [53]
Hastings Natural History Reservation, San Lucia Coastal Range, Monterey County 860 to 3,600 feet (262-1,050 m) [54]
central Sierra Nevada up to 6,000 feet (1,800 m) [44]
Pinnacles National Monument 1,200 to 3,000 feet (370-910 m) [22]
Donald and Sylvia McLaughlin University of California Natural Preserve 1,200 to 3,100 feet (370-950 m) [47]
Santa Ana Mountains average 3,500 feet (1,100 m) [60]
Oregon below 5,000 feet (1,524 m) [25]


SUCCESSIONAL STATUS:
Soap plant emerges soon after fire and is found in all stages of succession. Soap plant undergoes "vigorous" growth and flowering after fire [37]. Because soap plant is a somewhat shade-tolerant species, it is able to persist vegetatively in mature chaparral on a very low level. It survives under the closed canopy as dormant bulbs that occasionally send up leaves but seldom flower because of the low light levels. When soap plant does flower beneath the chaparral, the inflorescence suffers extensive animal grazing [6,32,33,37,47,57]. The appearance of soap plant in the bunchgrass prairie community of Bernal Hilltop, an undeveloped park in San Francisco, was noted after a 15-year absence due largely to dormant bulbs [41].

SEASONAL DEVELOPMENT:
Soap plant blooms from May to August throughout California, depending on the habitat and elevation [12,38,39,52]

FIRE ECOLOGY

SPECIES: Chlorogalum pomeridianum
FIRE ECOLOGY OR ADAPTATIONS:
Fire adaptations: Soap plant sprouts and seeds after fire. The perennating part of soap plant is a deeply buried, large bulb, which is its 1st defense against fire [10,20]. Second, soap plant is said to have an evolved fire-adaptive trait of "fire-stimulated flowering," since it flowers the 1st growing season after fire. Flowering is virtually absent beforehand [9,20]. Gill [20] states that flowering responses to fire may have arisen by direct selection for increased seed production but the significance of the trait could be related to various environmental pressures. For example, increased flowering and seed production after fire allows use of the available mineral seed bed, enhancing establishment. Alternatively, cyclic flowering stimulated by the passage of frequent fire could prevent the build-up of populations of specific predators to inflorescences, so successful reproduction can occur. Lastly, pollination could be favored by the removal of shrubs and the subsequent increase in light [20].

Fire regimes: Soap plant occurs in a narrow range of fire regimes. Chaparral communities, where soap plant is common, sustain frequent, stand-replacing fires. The high frequency of fire in chaparral communities suggests that soap plant has evolved with fire. The oak woodland and low-elevation ponderosa pine communities, in which soap plant also occurs, historically had frequent, low-severity fires. In ponderosa pine and some oak communities, low-severity surface fires are being replaced by high-severity, long-interval fires [8].

The following table provides fire return intervals for plant communities and ecosystems where soap plant is important. For further information, see the FEIS review of the dominant species listed below.

Community or ecosystem Dominant species Fire return interval range (years)
California chaparral Adenostoma and/or Arctostaphylos spp. <35 to <100
coastal sagebrush Artemisia californica <35 to <100
California montane chaparral Ceanothus and/or Arctostaphylos spp. 50-100 [40]
California steppe Festuca-Danthonia spp. <35 [40,55]
Jeffrey pine Pinus jeffreyi 5-30
Pacific ponderosa pine* Pinus ponderosa var. ponderosa 1-47
California mixed evergreen Pseudotsuga menziesii var. menziesii-Lithocarpus densiflorus-Arbutus menziesii <35
California oakwoods Quercus spp. <35 [3]
coast live oak Quercus agrifolia 2-75 [21]
canyon live oak Quercus chrysolepis <35 to 200
blue oak-foothills pine Quercus douglasii-P. sabiniana <35
Oregon white oak Quercus garryana <35 [3]
California black oak Quercus kelloggii 5-30 [40]
*fire return interval varies widely; trends in variation are noted in the species review

POSTFIRE REGENERATION STRATEGY [51]:
Geophyte, growing points deep in soil
Secondary colonizer (on-site or off-site seed sources)

FIRE EFFECTS

SPECIES: Chlorogalum pomeridianum
IMMEDIATE FIRE EFFECT ON PLANT:
Soap plant is most likely top-killed by fire. Underground bulbs are usually well protected from and resistant to even severe overstory fires [20]. Regeneration is likely from these deeply buried bulbs.

DISCUSSION AND QUALIFICATION OF FIRE EFFECT:
No additional information is available on this topic.

PLANT RESPONSE TO FIRE:
Soap plant responds favorably to fire. It undergoes "vigorous" growth and exhibits enhanced flowering in the first postfire year [4,6,33,37]. Keeley [32] suggests that soap plant may benefit from disturbances, such as fire, because of this increased opportunity for flowering. Populations increase after burning [48]. This relationship with fire suggests interference from overstory species directly affects abundance. Reynolds [44]states that soap plant prefers a burned or other disturbed site, and that it is dependent on periodic burning .

DISCUSSION AND QUALIFICATION OF PLANT RESPONSE:
Soap plant is part of the emerging postfire plant community, and is one of the most conspicuous herbaceous species found in chaparral and surrounding postfire plant communities [7,35,48]. Sampson and Burcham [49] list it is a "common invader species" in the 1st year after burning.

Soap plant's response to fire has been thoroughly documented in chaparral, where it is most commonly found. Sweeney [57] states that soap plant increases in numbers 2 to 3 years after fire. Sampson [48] ranks soap plant as fairly to very abundant on recently burned chaparral, peaking the 2nd postfire year and declining but persisting 3, 4, and 5 years after fire in chamise and manzanita/ceanothus communities. Barbour and others [4] convey that soap plant populations remain constant/persistent up to 4 years after fire.

FIRE MANAGEMENT CONSIDERATIONS:
To date (2006), there is no research providing management recommendations specifically for soap plant. Soap plant responds well to fire, given its fire-adaptive traits. Therefore, the use of prescribed fire as a means of reducing overstory interference to increase populations of soap plant appears to be a viable management strategy. In addition, there is no evidence to suggest the duration, magnitude, or severity of a fire event would have any adverse effect of the survival of the underground perennating bulb.

MANAGEMENT CONSIDERATIONS

SPECIES: Chlorogalum pomeridianum
IMPORTANCE TO LIVESTOCK AND WILDLIFE:
Soap plant is of some importance to livestock and wildlife throughout its distribution. Studies in Alameda and Santa Clara counties in central coastal California report that California ground squirrels eat soap plant [14]. A decline in abundance of soap plant is reported in Botta's pocket gopher-disturbed areas [26]. Since soap plant usually depends on disturbance, this decline suggests that pocket gopher herbivory may reduce soap plant populations. Populations could also be decreased due to herbivory by other rodents, rabbits, and mule deer. Rabbits graze seedlings and young plants, granivorous rodents eat soil stored seed, and mule deer graze and retard growth of plants at all stages [42].

Although livestock use of soap plant is not documented, it can be assumed that if soap plant is an available food source, it would be consumed. This is concluded from a study done on the Hastings Natural History Reservation and the Santa Lucia Coastal Range in Monterey County, where soap plant only appeared in uncultivated (unfarmed and ungrazed) stands [54].

Palatability/nutritional value: Studies done to date (2006) show that ground squirrels, pocket gophers, other rodents, rabbits, and mule deer consume young plants, seeds, and inflorescences of soap plant [14,26,33,42], suggesting that palatability is good.

Cover value: No information is available on this topic.

VALUE FOR REHABILITATION OF DISTURBED SITES:
Soap plant has been used in 2 instances for restoration. The US Army Corps of Engineers propagated soap plant from seed (in a nursery) to use for revegetating wildlife habitat in their Los Angeles District [23]. Seeds of soap plant were collected and hydroseeded on San Bruno Mountain, San Bruno State Park [63].

OTHER USES:
Soap plant was traditionally used by several California Native American tribes and early settlers. Tribes included but were not limited to the Miwok, Hulpumne Yokuts, and Wailakis [1,2,11,44]. Chlorogalum spp. are among the prominent genera gathered for their edible underground parts [1]. The bulb can be boiled to take out the soapy material and then eaten like a potato. The young shoots, when thoroughly roasted, are said to as "sweet as sugar" [11,58]. The Hulpumne Yokuts said soap plant was the "food that most abounds" [1]. Soap plant was used as emergency food during lean acorn years [1]. The value of Chlorogalum spp. was high for the Miwok. Highly sought for food and its medicinal use, soap plant was one of the most versatile plants in the Miwok economy [44].

Native Americans offered and introduced soap plant to early missionaries and explorers [1]. There are several traditional uses of soap plant. Fibers from the bulb portion of the plant were used to stuff mattresses and also used for brushes [11,12,58]. The leaves, which are flexible and half-succulent, were used to cover bread dough while baking. The leaves can also be pricked into the skin to form green tattoo marks [11]. The bulb was used for both food and utensils [2]. The bulb contains saponin, a soap substitute [13]. The bulbs are crushed and used as soap for clothes and bathing. When the bulb and young shoots are cooked, a resinous substance is exuded that was used as a glue for arrows [11,12]. The roasted bulb is used antiseptically as a poultice for sores. The Wailakis used it on the body for cramps and for rheumatism. A decoction of the bulb is also used as a diuretic and laxative [11].

Although illegal today, Native Americans used to crush soap plant bulbs and rub them into a lather. The lather was then thrown into streams and ponds to stun and stupefy fish, causing them to float to the top of the water where they were easily caught [11,12].

OTHER MANAGEMENT CONSIDERATIONS:
The literature reviewed to date (2006) uncovered no specific management strategies or concerns for soap plant.

Chlorogalum pomeridianum: REFERENCES

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