Encyclopedia of Stanford Trees, Shrubs, and Vines

Albizia julibrissin. (Albizzia j.). SILK TREE. Temperate Central Asia
Leguminosae (Pea family)

The feathery foliage resembles that of some acacias, and the flowers, consisting of a puff ball of pink stamens, are also similar. However, the flower is much larger and the stamens, unlike those of the acacia, are united at their bases. There are glands on the leaf stalks and at night the leaflets fold up. Late in the season numerous pods will be found containing collectible, shiny brown seeds. Separating the seeds from the pods is a therapeutic activity and a bowl of the seeds, as with honey locust and acacia seeds, can have the same effect as worry beads. Children with good hand-eye coordination might enjoy racing to separate the seeds from a pod or two.

A very attractive grouping, spectacular in late spring, is situated between the inner and outer quadrangles in the northwest corner. Albizzia and Chinese pistache are among the deciduous trees that exercise extreme caution before venturing forth new leaves; but in early April you can recognize these few remaining leafless species on campus, the Albizzia by last year’s seed pods and the pistache by the voluminous masses of pollen cones. Several specimens can also be seen on San Francisco Terrace and on the northwest side of Dining Services, off Pampas Lane. Julibrissin is the Persian name of the tree but it ranges across Asia to China, and the hardy ‘Rosea’ comes from Korea. It is widely planted in southern Europe. The seeds germinate readily if left to stand overnight in a cup to which boiling water is added.

In the trecento and quattrocento, the noble Albizzi family competed for power over Florence and are remembered to this day by the Via degli Albizzi situated in the part of the city that retains the old rectangular Roman street layout. No true humanist would use the ignorant spelling Albizia. Francesco degli Albizzi brought the silk tree into gardens in 1749.

Illustration right: McMinn, Howard E. and Evelyn Maino. 1951. An illustrated manual of Pacific coast trees; with lists of trees recommended for various uses on the Pacific coast by H. W. Shepherd. 2d ed. Berkeley, Calif.: University of California Press.

Illustrations (links open new windows): typical ground litter | Silhouettes from Trees of Stanford & its Environs

Additions/Revisions: The Pea family is among the largest flowering plant families with about 18,000 species in 630 genera worldwide. Caesalpina is the type genus for the Fabaceae subfamily Caesalpinioideae, following Cronquist (1981). This subfamily is intermediate in flower morphology between the other higher-level classifications Mimosoideae and Faboideae (or Papilionoideae), and similar to the Cercidoideae (Bauhinia, Cercis). The Faboideae is the largest subfamily and includes plants with papilionaceous, "butterfly-like", corollas (with standard, wings, and keel)—as the common garden pea.

All subfamilies are well represented on campus for closer study. Caesalpinioideae and Mimosoideae include mainly tropical trees with pinnately or bipinnately compound, alternate leaves. Mimosoideae flowers are regular (radially symmetrical), the corolla with equal petals often fused into a tube. Campus representatives include Acacia, Albizia, and Gymnocladus. Caesalpinioideae flowers are usually zygomorphic or bilateral (divisible into equal halves in one plane only). As with Caesalpina, the petals are distinct, the uppermost often smaller than the laterals. It would be instructive to work out the subfamilies of the many other campus peas (genera listed in the family index) from field observation throughout the year.

— further reading: Wendy Zomlefer, Guide to Flowering Plant Families, Univ. of North Carolina Press, 1994.

Name derivation, genus | species

Related material: Canopy Trees for Palo Alto Tree Library

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