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Quillaja saponaria, or Soapbark Tree as it is commonly referred to, is a tree in the Rose family (Rosaceae) from Chile. The
name Quillaja comes from the Chilean name quillai which is a modification of the word quillean, meaning to wash.
The colloqial name was in reference to the suds-making saponins present in the bark. It is a slender, upright evergreen tree
growing to 30-45 ft. tall with pendulous branchlets. The bright green oval leaves
are 1-1 ½ inches long and ½ to ¾ inches wide with slightly toothed margins that become almost entire towards
the leaf base. Cream-white star-shaped flowers, about ½ inch across are freely produced at the ends of the branchlets
during May and June and somewhat into summer. The fruit, ¾ inch or more across, is a rosette of 5 leathery lobes that
matures in fall.
Quillaja is cold hardy into at least the high teens F. In Santa Barbara in the winter of 1990 we had 18 ° F without damage. It is tolerant to adverse soils and can withstand
drought conditions but looks much better when given regular deep irrigation or when planted in a lawn.
Young plants tend to be bushy and need occasional pruning when young but eventually form narrow, almost collunar, trees that
are ideal for narrow confines. Another usage is as a tall hedge.
Aside form its ornamental qualities Quilaja has several other virtues. One that can expoited while still ejoying the ornamental qualities is
that this tree is an attractant to beneficial insects. Cornflower Farms of Elk Grove, California has been marketing this tree as a "Beneficial Insect Plant", attracting to the garden such
insects such as lacewings, hoverflies, lady beetles and wasps.
The other attribute has to do with the substances in the bark that has both caused a medical stir as well as put the plant on poisonous plant lists.
Quillaja saponaria is listed in Poisonous Plants of California (Thomas Fuller and Elizabeth McClintock, UC Press 1986) because
of toxic saponin glycosides. These toxins characteristically affect cold blooded animals but if the gastrointestinal tract of
warm blooded animals has been injured they can be absorbed. Plants containing saponins are typically bitter to the
taste and are rarely browsed. It is Quillaja's bark that contains saponin and there is no mention of any known poisoning associated with it.
In recent medical studies it is this same saponin that has been determined to have potential. The saponin QS-21, derived from the bark of Quillaja saponaria,
has shown great potential as an adjuvant with a number of vaccines. Unfortunately this has caused the decline of native stands of the tree in Chile and
has sparked an interest in cultivating the tree as a agricultural crop.
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