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.