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What’s Blooming: Sweet Gum’s Bittersweet Horticultural Legacy

December 14, 2009

What's Blooming

 

On the south side of the creek that meanders through the Arboretum’s Meadowbrook section three tall, upright trees can be seen right now covered in brightly colored fall foliage. Commonly called "Sweet gum," Liquidambar styraciflua, is native to Central America, Mexico, and the Southeastern United States where it is a significant percentage of newly regenerated hardwood forests. Liquidambar grows rapidly in regenerating forests because it has the ability to fix nitrogen in the soil. 

Liquidambar’s name derives from the liquid, amber-colored, resin the tree produces to protect itself from insect attack. This resin has been used by Native Americans in Mexico and North America as a chewing gum and as a medicine for healing wounds. The Aztecs were even more creative with the gum, using it as ceremonial incense and adding it to smoking tobacco to create a potent sleep-aide.

Liquidambar wood is beautiful; polished cross sections reveal red heartwood surrounded by a contrasting band of bright white sapwood. Unfortunately the moisture content of the wood and its poor durability make it almost impossible to work with; items made from the wood warp and wear out rapidly. Furniture makers can still exploit the Liquidmabar wood’s natural beauty by applying it as a veneer to furniture constructed of more durable but less beautiful woods like pine.

During the late 1970’s and throughout the 1980’s, Liquidambar styraciflua was an extremely popular landscaping and street tree. Three varieties introduced in the late 50’s and early 60’s by the Saratoga Horticultural Foundation in Palo Alto came to dominate the California urban landscape because of their pleasing forms and reliable fall coloration. ‘Palo Alto’ has orange and red fall leaves, ‘Festival’ has a confetti-like combination of red, yellow and pink, and ‘Burgundy’ is a variety that reliably turns a dark red here in late fall. These are the varieties planted along the stream in the Meadowbrook section.

Liquidambar styraciflua

For a while Liquidambar seemed like the perfect tree for California; a deciduous tree that seemed to thrive here and gave migrants from the east coast a taste of the colorful fall display of leaves they were used to back home. It was also fast grower that didn’t get out of bounds (cultivated Liquidambar rarely get over 60-70 feet tall) and a tree that seemed to thrive anywhere because of its nitrogen fixing abilities. But when the Saratoga Horticultural Foundation introduced the trees they paid little attention to a characteristic of the tree that would later create what could be termed a horticultural disaster.

As Liquidambar matures its nature changes; the trees develop a propensity to form damaging surface roots and their production of spiny seed-balls increases. This makes mature Liquidambars quite a nuisance and liability; a fact that many property owners and cities would become painfully aware of after removing tens of thousands the trees and repairing the expensive damage caused by them to nearby structures.  A study published in Western Arborist that surveyed tree damage in several Southern California cities found that the ubiquitously planted Liquidambar accounted for the greatest number of trees causing damage. In the city of Alameda it was found that 69% of the Liquidambars planted in that city were damaging or starting to damage structures.

Currently Liquidambar styraciflua is not the easy landscape choice it used to be, but it still has advantages in some situations; it is now recommended that the trees be planted in locations that are at least 15-20 feet from any structures, and in areas where their copious production of spiny seed balls is not a problem. They should never be planted as street trees.

Chorisia Trees Greet the Fall With Hot Pink Pizzazz

October 04, 2009

What's Blooming

Chorisia speciosa
Chorisia speciosa grown from seed here at the Arboretum

Chorisia speciosa seedling

 

Named after a German artist, Ludwig Choris, the Floss silk tree, Chorisia speciosa, is called ‘Palo barracho rosada’ (‘rosy drunken stick’) in its native Argentina because of its odd-angled branches and pink flowers.  In the fall it produces a spectacular show of orchid-like pink blooms and then a large crop of avocado like green pods that eventually explode in the spring to produce cotton-like masses of seed impregnated fibers. Here at the Arboretum parrots swarm to the newly exploded fruit to consume the seeds and in the process cause the fibers to scatter in the warm spring breeze like snow. This fiber is resistant to insects and rotting and has been used for pillow stuffing and, because it floats, has been used in life vests and preservers as well. Probably the most interesting use of this fiber has been to acoustically deaden recording studios and radio broadcast rooms.  Besides using its fiber Argentineans and Brazilians have used the wood for canoes (it’s almost as light as balsa) and the tree is planted extensively in its native range as an ornamental.

C. speciosa 'September Splendor'

Chorisia speciosa 'September Splendor' is usually the first to bloom here at the Arboretum.

 

In its native, mostly frost-free range Chorisia endures dry seasons and droughts by losing its leaves; however unlike trees in temperate regions where a thick layer of bark is needed to insulate the sensitive layer of food and water transporting tissue known as the vascular cambium from the freezing cold, Chorisia's trunk has a very thin layer of protective tissue. This thin layer allows light to pass through photosynthetic cells containing chlorophyll. This is why Chorisia's trunk appears green. Because the trunk has no bark to protect it from animals that might eat it, large spines cover it and the larger branches of the tree -this is why you'll rarely see a Chorisia planted next to an athletic field!

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