The Mimosaceae are mostly tropical and subtropical trees and shrubs comprising about 40 genera and 2,000 species. The leaves are nearly always alternate, stipulate, and bipinnately compound (rarely once-pinnate) They usually have swollen petiole bases called pulvini that commonly function in orientation of the leaves (remember the sensitive plant, Mimosa pudica). The inflorescence is commonly a capitulum (also called a head). The flowers are hypogynous to slightly perigynous, have radial symmetry, petals that are valvate in bud, and commonly a 5-parted calyx and corolla. The stamens are distinct to strongly monadelphous, numerous (rarely as few as 10), and are generally more showy than the perianth. The pistil is simple, comprising a single style and stigma, and a superior ovary with 2-many marginal ovules in a solitary locule. The fruit is usually a legume.

Each "thumbnail" image below is linked to a larger photograph.

Acacia koa, koa. The simple lateral foliar appendages (phyllodes) seen in the upper part of the 2nd photo and in the 3rd photo are not typical for this family. this species initially produces bipinnate leaves (lower leaves in 2nd photo) typical of other Mimosaceae but in the sapling stage begins to produce these modified leaves that aid in conservation of water in the habitats where these unusual phyllodinous acacias grow.  Note the pods (legumes) and also the small flowers compacted into heads in the 3rd photo. The styles of individual flowers can be seen to be exserted beyond the stamens. 
Adenanthera pavonina, coralwood, false wiliwili. Tree from S. E. Asia with pinnate leaves and rather inconspicuous clusters of small yellow flowers. The scarlet "Circassian" seeds are lens shaped, about 1/3 inch in diameter, and are used in lei construction. The red heartwood is valued for cabinetwork and as a source of dye.
Albizia lebbeck, siris tree.  Tree from tropical Asia
Calliandra calothyrsus, powderpuff. Shrub from Mexico and South America with red "powderpuff" clusters of flowers.
Calliandra inaequilatera. Note the valvate nature of the petals in bud stage and the mass of withering stamens in the older inflorescence.
Leucaena leucocephala, koa haole. Note the bipinnately compound leaves and the white flowering heads. Legumes are also visible. In the close-up of the flowering head, the style of each flower can be seen as a straight, white cylindrical structure that extends beyond the stamens.
Mimosa pudica, sensitive plant. Note the typical flowering head with stamens dominating as the attractive component of the flowers. In this family the leaves and leaflets are often capable of movement due to changes in the water pressure of the swollen leaf and leaflet bases (pulvini). In many species of this family the leaves assume a folded or "sleeping" posture at the end of the day that is triggered by a decrease in light level. However, the sensitive plant is also capable of rapid movement in response to touch or application of heat.
Paraserianthes falcataria, albizzia.
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Parkia javanica.
Pithecellobium dulce, opiuma. Notice the clusters of small heads and the corkscrew-shaped legumes. The spongy white aril that envelopes the seed (lower photo) is edible.
Prosopis pallida, kiawe. The flowers of this species are in a dense spike.
Samanea saman, monkey pod; rain tree, 'ohai. Stunning shade tree from tropical America, with large, dome-shaped canopy. The attractive wood is crafted into platters and bowls that are commonly marketed in Hawaii. The pods have a sweet, sticky brown pulp, and are fed to cattle in Central America. The 3rd photo shows the details of a single head. Note the relative size of the perianth and androecium, and the numerous stamens.

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