Arboretum Images 5

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Palomar College Arboretum Images 5: Legumes #2
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3. Subfamily Mimosoideae:

Members of the subfamily Mimosoideae have flowers with radial symmetry, small, inconspicuous corollas and numerous, showy stamens. The flowers are typically in many-flowered heads or spikes. This subfamily includes Acacia (wattle), Albizia (silk tree), Samanea (monkeypod), Prosopis (mesquite) and Calliandra (powder puff).

Plume albizia (Albizia distachya). Although native to Australia, this species spreads readily by seed and becomes quite invasive in southern California.

Mimosa or silk tree (Albizia julibrissin). This beautiful species of Albizia has an enormous natural range, including southern and eastern Asia, from Iran east to China and Korea. It is naturalized in the southeastern United States and commonly planted as a shade tree in San Diego County, including the campus of Palomar College. Its spreading growth form is similar to the spectacular rain tree (monkey pod) of Hawaii and tropical America.

 The Fabulous Rain Tree or Monkey Pod of Hawaii & Tropical America 

Left: Pink powder puff (Caliandra haematocephala), a beautiful tree native to Bolivia. Right: Sweet acacia (Acacia farnesiana), a very fragrant tree that is naturalized throughout tropical countries of the world. It is probably native to the southern United States, Mexico and tropical America. Both of these species have flowers with reduced petals and conspicuous stamens, typical of the subfamily Mimosoideae.

Brazilian flame bush (Calliandra tweedii)

  Seeds & Fruits Dispersed By Wind  
The Legume Family (Fabaceae)

Silver wattle (Acacia dealbata), a beautiful Australian tree with silvery-gray bipinnate leaves. The leaf petiole contains a prominent gland with paired (jugate) glands on the rachis (red arrow). In Central American thorn acacias, similar petiolar glands supply symbiotic ants with carbohydrate-rich nectar. The ants protect the trees from browsing herbivores in one of nature's most remarkable interrelationships between an insect and a tree.

Acacia Glands & Symbiotic Ants
Giraffe Feeding On Acacia Leaves
 Acacia: Remarkable Genus Of Trees 

Knife-leaf acacia (Acacia cultriformis), a beautiful species from eastern Australia. The leaves are modified petioles called phyllodes. Other species have compound leaves composed of tiny leaflets.

 Acacias With Pinnate Leaves & Phyllodes  

Although the seed pods in the above image are from the Costa Rican Enterolobium cyclocarpum, the foliage is from a tree in the Palomar College Arboretum that might be E. contortisiliquum. The mystery tree has 4 to 8 pairs of pinnae, 15 to 22 pairs of leaflets, and leaflets that are 15 mm (5/8 in) to 19 mm (3/4 in) long. According to Hortus III, E. contortisiliquum has 3-14 pairs of pinnae, 10-15 pairs of leaflets, and leaflets up to 19 mm; E. cyclocarpum has 7-10 pairs of pinnae, 20-30 pairs of leaflets, and leaflets up to 13 mm long. The leaflet dimensions are closer to E. contortisiliquum; however, the leaflet number approaches E. cyclocarpum. Without mature seed pods, the ID is inconclusive at this time.

Seeds and pods of Enterolobium contortisiliquum, a large tree native to Brazil.

The guanacaste tree (Enterolobium cyclocarpum) is a large canopy tree native to the Guanacaste Province of northern Coasta Rica and naturalized in southern Baja California and the Hawaiian Islands. It has fernlike, twice pinnately-compound leaves and distinctive seed pods. The word "guanacaste" is of Nahuatl origin and signifies "ear tree." The peculiar coiled, leathery pods superficially resemble the shape of a human ear. The nutritious pods are used for stock feed and the bark and wood are used for tanning and lumber. One of the most interesting uses involves the hard, woody seeds which litter the ground beneath large trees. Guanacaste seeds have a distinctive brown "eye" and make some of the most striking seed jewelry in North America, especially when they are enhanced with a fine finish of tung oil or lacquer. In Costa Rica the seeds are used in a variety of bracelets, necklaces and earrings (see the following image).

Seeds and pod of the Guanacaste tree (Enterolobium cyclocarpum), a large canopy tree native to the Guanacaste Province of northern Costa Rica. The beautiful seeds are commonly used in jewelry.

  See Article About Botanical Jewelry  

Guanacaste seedling (Enterolobium cyclocarpum) from seeds originally collected in the Guanacaste Province of northern Costa Rica about 20 years before. The seeds remained viable in a flask for approximately two decades.

Wild tamarind (Leucaena leucocephala) photographed along a roadside on the island of St. John (U.S. Virgin Islands). This species produces thousands of flattened legume pods containing shiny brown seeds. It is generally thought to be native to Mexico and Central America, but is naturalized throughout tropical regions of the world. Right: Close-up view of globose inflorescences of this species in the Palomar College Arboretum. The flowers have reduced petals and conspicuous stamens, typical of the subfamily Mimosoideae.

Wild tamarind (Leucaena leucocephala) produces thousands of elongate, flattened legume pods containing numerous seeds. The shiny brown seeds are commonly strung into elaborate necklaces in Caribbean and Hawaiian islands. They are often used as spacers between bright red seeds from coral trees (Erythrina) or other species.

  See Beautiful Seed Necklace with Wild Tamarind Seeds  


Rapid Movement Of The Sensitive Plant

The sensitive plant (Mimosa pudica) is a pantropical weedy herb in the legume family (Fabaceae). The pinnately compound leaves are composed of numerous tiny leaflets. When touched, the leaflets begin to fold up very rapidly and the leaf stalk (petiole) suddenly bends downward. [Sleep movements also occur in the sensitive plant and in many other species of leguminous trees and shrubs in which the leaflets slowly fold up at night.] These plant movements in response to a stimulus (called nastic movements) are associated with loss of tugor pressure in the leaves. The sensitive plant is especially interesting because of the rapidity of the wilting process, an entire leaf suddenly drooping after it has been touched. As one leaflet folds up, the stimulus moves to other parts of the leaf until all the leaflets and adjacent leaves have folded up. Two distinct mechanisms, one electrical and the other chemical, appear to be involved in the rapid spread of the stimulus in sensitive plants. At the bases of the leaflets are jointlike thickenings called pulvini, with a large pulvinus at the base of each petiole. When a leaf is stimulated by touch, heat or wind, there is a chain reaction in which potassium ions migrate from one side of each pulvinus to the other side. This is followed by a rapid shuttling of water molecules from parenchyma cells in one half of the pulvinus to cells in the other half. This action results in loss of turgor pressure that causes folding of the leaflets and eventually the entire leaf. The entire process may take only a few seconds. When the leaflets fold up and instantaneously become wilted, it is often difficult to see where the leaf was in its original turgid state. It has been suggested that this rapid wilting process may be an adaptation to grazing mammals or ravenous insects.

A sensitive plant (Mimosa pudica) on the island of Hawaii before and after being touched. The left photo shows fully turgid leaves (pinnae) with all the leaflets (pinnules) fully extended for maximum light absorption. In the right photo the leaflets have folded up and the leaves are barely discernable. Can you spot the five main compound leaf divisions (pinnae) that have closed up in the right photo?

A Sensitive Plant In The Palomar College Arboretum

A sensitive plant (probably the genus Mimosa) growing in the Palomar College Arboretum. The flowers resemble Mimosa pudica); however, this is a woody shrub two meters tall. In addition, the stems have very long stipular spines at the bases of the compound leaves. It may be M. pigra, a widespread tropical shrub appropriately called "giant mimosa" or "catclaw mimosa."

A sensitive plant before and after being touched. The left photo shows fully turgid leaves (pinnae) with all the leaflets (pinnules) fully extended for maximum light absorption. In the right photo the leaflets have folded up.

A shrubby sensitive plant (Mimosa sp.) from Central America. Vegetatively it is similar to the pink-flowered M. pigra, a common roadside shrub of Costa Rica. The latter species is a very invasive weed throughout tropical regions of the world, particularly the Northern Territory of Australia. The flowers and pods are typical of the subfamily Mimosoideae. The leaflets in left photo have closed up in response to being touched.