22. Silk Tree

Also called the Mimosa Tree or Powderpuff Tree

Specimen Size: 39.9ft tall,18.25in in diameter.

Location: West of the HUB entrance with the Starbucks annex, north of the concrete patio. Unfortunately, this tree was removed in early 2024 due to trunk rot. It will likely be replaced elsewhere on campus. Please stay tuned for updates on a replacement.

This is the Silk Tree, also called the Mimosa or Powderpuff tree, and it is called such because of the shape of these very pretty flowers, which are composed of silklike thread and resemble a bright pink cotton ball. These flowers, which come in bunches, provide a show which lasts the entirety of summer, and it is no surprise this tree was brought to the America’s as early as 1749 for use as an ornamental. The leaves are also exquisite, appearing late, often months after most everything else has leafed out. They are bipinnately compound, each leaf having leaflets which in turn have their own leaflets. They are dark green above and light green beneath and quite large. The flowers give way to seed pods which rarely achieve growth in Seattle’s climate. One most beautiful time to visit this tree is during a nighttime rainstorm, when the leaves droop and fold as if the tree is sleeping, thus giving rise to its native Japanese name Nemunki, meaning sleeping tree. 

Historical Background: This species was introduced to the United States in 1745 as an ornamental due to its large and fragrant flowers. This tree can be a strong competitor in open areas and may outcompete native species. Each night and while it rains, the leaves of the silk tree close slowly, the leaflets bowing down as if the tree was sleeping. The synonym nemu tree is an adaptation of the Japanese name nemunki, meaning sleeping tree. The bark or cortex is used to cure bruises and as a vermicide. The wood of the silk tree is dense, hard, and strong and has been used to make furniture.

Non-Native

Native Range: Iran, India, China, Japan

Identifying Features: This deciduous tree is late to come into its summer foliage, which is composed of bipinnately compound leaves of pale green, which look fernlike in nature. The crown is broad and flat, composed of spreading branches and, when flowering, distinctive pinkish cotton ball-esque flowers crowded into clusters. The flowering season for this tree is particularly extensive. This tree, like the Honey Locust seen just a moment ago, is in the legume family, and as such it too gives rise to those oblong seed pods so indicative of that group, however, one would not want to eat these seeds as they are not edible).

Identifying Features In Depth:

1. Form: A small ornamental up to a height of only about 20’ (6m), with short trunk or cluster of trunks rising to a crown that is broad and flattened composed of spreading branches.

2. Leaves: Leaves are a pale green, bipinnately compound from 6-15” (15-38cm) in length and covered with fine hairs. Each has 5-12 pair of side axis, and each of these has 15-30 pairs of oblong leaflets of about 15 mm in length.

3. Bark: Bark is blackish to gray and nearly smooth. Twigs often have angles and zigs.

4. Reproductive Bodies: The most distinguishing feature of this tree, each flower is over 1” (2.5cm) in length and composed of long thread or silk like pink stamina turning white at the base and crowding into balls at the end of the twigs. They are extremely persistent, throughout the summer. These give rise to fruiting bodies in a bean pod like structure 5-8” (13-20cm) in length, pointed and flat and a yellow brown. This oblong structure contains flattened shiny brown seeds which mature in mid summer.