Small Flowered Soap Plant

Small-flowered soap plant, or amole, or simply soap plant (Chlorogalum parviflora) is a fragile-looking member of the agave family that looks like a tiny lily and is native to only a small region of coastal southern California and northern Baja, California. Soap plant has an underground bulb that allows it to persist during unfavorable conditions, including drought and wildfire.

Soap plant is one of several unrelated plants that contain a type of glucoside called saponin. When mixed with water, saponin produces a lather and cleans like soap. Native Americans used the bulbs of soap plant to bath and to washcloth. Bulbs were also roasted and eaten, used to stun fish for easy harvest, and used as a glue.

Description ^59,261,342

Small flowered soap plant grows from an underground bulb, 1½ to 3 inches (4 – 7 cm) long, with a brown, membranous coat. The bulb contains saponins,³⁴² a type of glucoside that produces foam when agitated in water, hence the common name. In January or February, the bulb begins to produce a distinctive, spidery basal rosette of a few leathery leaves. Leaves are green, up to eight inches (20 cm) long and 1/3 inch (1 cm) wide, with strongly undulating margins, and without petioles. Leaves die back before or just after the onset of bloom.

A single, leafless green or reddish-brown flowering stem, up to four feet (1.2 m) in height produces a few, long, unbranched side branches. Clusters of one or a few flower buds are produced at discrete nodes along the stems, which may zigzag at the nodes. At any time, only a few scattered flowers open on short pedicels along a branch. Flowers are bisexual and radially symmetrical, about 1/3 inch (1 cm) across. Sepals and petals are similar (together called “tepals”). There are six white or pinkish tepals, often with a central green and or pink stripe and a green base; tepals are strongly curved backward. There are six stamens and a single pistil with a rounded, green ovary and a single, thin, unbranched style. Stamens and style extend well beyond the throat of the flower. After fertilization, the tepals twist together around the developing fruit, ultimately falling away as the fruit approaches maturity. Flowers bloom for just one day, opening in the early morning and closing at sundown. ²⁹⁰ Our soap plant blooms from May into August.¹

The fruit is a dry, spherical, three-chambered capsule, each chamber with one dark, rounded seed.

Classification  

Small flowered soap plant is a perennial Monocotyledon (Monocot) in the agave family (Agavaceae). Monocots are an early offshoot of flowering plants, partly characterized by having a single cotyledon (instead of two), by having parallel veins in the leaves (instead of reticulated) and by having flower parts in multiples of three (instead of fours or more).¹⁷⁶

The agave family is in a state of flux.⁴¹ As of 2017, the source we follow,² retains the agave family as a separate family. Others place it as a subfamily of the asparagus family (Asparagaceae).^41,143 It has also been considered a subfamily under the lily family (Liliaceae).¹¹

Members of the agave family are often found in dry habitats.⁷⁶ They are characterized by rosettes of stiff, fibrous leaves^11,76 and by a fruit with two or more chambers that becomes dry and splits open at maturity.⁴⁴ Many have large, erect, conspicuous flower clusters,⁴¹ although small flowered soap plant is clearly an exception. In the Reserve, we have four species in the agave family. In addition to the delicate soap plant, there are three tall, statuesque agaves and yuccas: Shaw’s agave (Agave shawii), Mojave yucca (Yucca schidigera) and chaparral yucca (Hesperoyucca whipplei).

Chlorogalum is a small genus of only five species, all restricted to California and northern Baja California.⁷ Small flowered soap plant is the only species found in the Reserve.

NOTE: In 2018, several years after this writing, the genus Chlorogalum was split into two.⁵³⁵ The small flowered soap plant and another species were moved into a two-species genus, Hooveria, based upon DNA analyses, the fact that they bloom diurnally instead of nocturnally and small morphological and cytological differences.

Ecology ³⁴¹

Small flowered soap plant is a “geophyte”, or “earth plant”. While the precise definition of this term is being debated, the quintessential geophyte is a perennial herb with an underground storage structure, such as a bulb or corm or tap root that can persist without top growth from two or more years. During unfavorable environmental conditions, the top part of the geophyte dies to the ground, and only the subsurface storage organ persists, providing the energy for the plant to resprout when conditions improve. Geophyte is not a taxonomic category, but an ecological strategy.

Geophytes are most highly evolved in Mediterranean climates where the subsurface organ provides a survival mechanism for the summer drought.¹⁴ In some geophytes, the same strategy has further evolved to promote survival in the presence of wildfires. These geophytes need full sun and tend to disappear as surrounding vegetation shades them out. Some geophytes can survive underground for many years until a burn clears back the overlying vegetation. Populations of these plants seem to explode after a fire, presenting colorful displays the following spring.

Human Uses  

The most widely spread species of soap plant in California is the wavyleaf soap plant (C. pomeridianum), which is not found in the Reserve.⁴⁸ The wavy leaf was also the most widely used by native Americans and is the most widely discussed in the ethnobotanical literature.  The few references that mention the small flowered soap plant,^17,282,342 suggest the two species were generally interchangeable. The bulbs of both were roasted and eaten, rubbed on hands, hair, and cloth to be used for soap, crushed and tossed into ponds to stun fish for easy capture, and even used as a glue.^{15,17,41,282,342}

On the other hand, the bulbs of the wavyleaf soap plant are covered in a coarse fiber jacket and the fibers were often used to make brushes.²⁸² Bulbs of our soap plant lack these fibers.^2,342

There is evidence that some tribes managed soap root populations, removing only the larger bulbs and replanting the smaller ones, and even burning the area to recycle nutrients and remove encroaching vegetation.^67,341

Interesting Facts  

A frequently used alternate common name for all the soap plants is “amole”,^1,8 after the Spanish name for various plant roots used as soap. This, in turn, comes from the Nahuatl (Aztecan) word “ammoli” or soap plant.^282,291