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Economic Plant Photographs #24

American Pokeweed & Two Related Tree Species
In Memory Of Remarkable Ombu Hybrid At Palomar College

Pokeweed Family (Phytolaccaceae): Pokeweed

Pokeweed (Phytolacca americana) is a robust perennial potherb native to the eastern United States. It belongs to the pokeweed family (Phytolaccaceae), a small family found mostly in Africa and the New World. In addition to pokeweed, it also includes several enormous South American trees and some unusual serpentine vines of the tropics. Poke is derived from the Algonquian Indian word "pakon" or "puccoon," referring to a dye plant used for staining. It is sometimes spelled polk and the leaves were reportedly worn by enthusiastic supporters during the campaign of James K. Polk, 11th president of the United States. The generic name Phytolacca is derived from the Greek word phyton (plant) and the French lac (lake--a dark red pigment), referring to the crimson juice of ripe berries. Pokeweed may grow to nine feet tall, with large, alternate leaves and a carrotlike taproot. It may become a very invasive weed in southern California gardens and is difficult to eradicate when it becomes well-established. Greenish-white flowers are produced in long clusters (racemes) that droop due to the weight of ripening fruit. The flattened berries change from green to shiny purplish-black. Ripe berries yield a crimson juice that was used as a substitute for red ink and to enhance the color of pale wines. The coloring of wine with pokeweed berries has been discouraged because they are very poisonous.

Freshly cut young leaves and shoots may be cooked and eaten like spinach. They should be boiled twice, and the first water being discarded. In 1969, when astronaut Neil Armstrong walked on the moon, a popular song on the radio was "Poke Salad Annie." Some versions were spelled "Polk Salad Anne." The song depicted a poor southern girl who picked a wild plant called pokeweed for a vegetable. The greens are also called poke salet, and they are sometimes canned and sold in markets.

Popular Version of "Polk Salad Anne" by Tony Joe White
If some of ya'll never been down south too much
Some y'all never been down s-
I'm gonna tell you a little story so's you'll understand what I'm talkin' about
Down there we have a plant that grows out in the woods, and the fields
And it looks somethin' like a turnip green
Everybody calls it polk salad
Now that's polk salad
Used to know a girl lived down there and she'd go out in the evenings and
Pick her a mess of it
Carry it home and cook it for supper
Because that's about all they had to eat
But they did all right

  Lyrics To "Poke Salad Anne" & Recording Artists  

Naturalized pokeweed (Phytolacca americana) in Twin Oaks Valley, San Diego County.

Left: Fruiting branch of pokeweed (Phytolacca americana) showing the characteristic dark green leaves and purple-black berries. Right: A can of poke salet greens, the young, tender leaves of pokeweed.
Several toxins have been identified in species of Phytolacca, usually concentrated in the roots, berries and seeds. These poisons include an alkaloid (phytolaccine), a resin (phytolaccatoxin), and a saponin (phytolaccigenin). According to W.H. Lewis and M.P.F. Elvin-Lewis (Medical Botany, 1977), the most serious health hazard from Phytolacca comes from a very toxic plant protein called a lectin. Lectins can cause red blood cells to clump together (agglutinate) and may stimulate abnormal cell division in quiescent B and T-lymphocytes. Lectins are the primary toxic principle in the world's deadliest seeds, including the castor bean (Ricinus communis) and prayer bead (Abrus precatorius). The agglutination property of lectins serves a useful purpose in legumes, by binding and localizing essential nitrogen-fixing bacteria within the swollen nodules of roots.

Phytolacca Family (Phytolaccaceae): Ombu Tree

Of all the species of Phytolacca, the most remarkable is the ombu tree (P. dioica) of the Argentine pampas. Ombu trees (also called umbu trees) grow to a height and spread of 60 feet (20 m) or more, often with multiple trunks developing from an enormous base resembling a giant pedestal. The huge base may be three to six feet tall (1-2 meters) and 95 feet (30 meters) in circumference.

Photo by Tony Rodd licensed under CC BY-NC-SA 2.0
This tree is sometimes called a giant "herb" because it doesn't have a solid, woody trunk with hard, lignified growth rings. Its trunk consists of anomalous secondary thickening rather than true wood. As a result, the ombu grows fast but its wood is soft and spongy. The trunks store water and have structural integrity due to turgor pressure. When dry, the trunk resembles concentric layers of cardboard. True wood is composed of densely packed dead xylem cells with lignified secondary cell walls.

Left: A cross section of an ombu limb showing harder (more resistant) xylem tissues separated by spongy parenchyma that has since disintegrated.

Ombu trees are native to the grassy pampas of Argentina, usually widely spaced and the only trees for miles. They are called "lighthouses of the pampas" by gauchos who use them for welcome landmarks and shelters. The massive, fire-resistant trunk contains water storage tissue, an excellent adaptation for raging grass fires that periodically sweep across the pampas. Even young trees develop the characteristic enlarged (caudiciform) base, an obvious advantage in surviving prolonged months of drought during the dry season.

Several specimens of ombu trees were planted at the Palomar College Arboretum, including another interesting species from Peru (P. weberbaueri) and an unusual hybrid between the two species. The leaves have natural insecticidal properties and many years ago a professor of veterinary medicine (possibly from Cornell University) stopped by Palomar College to collect leaves for his research. He apparently located our trees on Wayne's Word, but unfortunately, I cannot find my details of his visit.

The North American pokeweed (Phytolacca americana) is synoecious, a term applied to a plant (or a species) in which the flowers are perfect (bisexual) with male stamens (androecium) and female pistil (gynoecium). Some references state that flowers of Phytolacca may also be unisexual, in which case, the species can be dioecious. Although the specific epithet for the umbu tree is dioica, plants I examined in the Palomar College Arboretum had bisexual flowers, with stamens (androecium) and a pistil (gynoecium). Racemes in fruit were sometimes lacking evidence of stamens. In some flowers with mature stamens the gynoecium was not fully developed. According to the scholarly textbook Plant Ststematics: A Phylogenetic Approach by W.S. Judd, et al. (2008), the flowers of Phytolaccaceae are usually bisexual.

Left: Massive base of an ombu tree (Phytolacca dioica). Right: The foliage and inflorescences (racemes) of the ombu tree. The older, far right raceme is composed of numerous multicarpellate fruits, each representing a separate flower.

Inflorescence and bisexual flower of ombu tree (Phytolacca dioica).

Close-up view of an immature, bisexual flower of Phytolacca dioica showing a central gynoecium (red arrow) surrounded by many stamens (androecium).

Phytolaccaceae: Phytolacca weberbaueri

Left: The Peruvian species Phytolacca weberbaueri in the Palomar College Arboretum showing the large base which is similar to the Argentine ombu tree (P. dioica). Right: A hybrid between P. weberbaueri and P. dioica in the Palomar College Arboretum. This large tree developed a massive trunk greater than one meter in diameter in only 25 years.

Hybrid Phytolacca weberbaueri At Palomar College

In the early 2000s this was the largest tree on the Palomar College campus. For many years I hiked up to this spot, with Owens Peak in the distance, with my biology and botany classes. It is a hybrid between the Peruvian species Phytolacca weberbaueri and the Argentine ombu tree (P. dioica). In the distance is the Palomar "P" on the southwest slope of Owens Peak. Unlike the blue-gray monzogranite bedrock on the Palomar College campus, the summit of Owens Peak is composed of Santiago Peak Metavolcanic rock. This dark, fine-grained, very hard rock dates back to the Jurassic Period, 135-180 million years ago, to a time when dinosaurs walked the earth. This heavy rock is resistant to erosion and forms some of the higher topography in coastal San Diego County.

Unfortunately, this marvelous tree succumed to a devastating soil fungus in 2014. It was identified by horticulturist Tony Rangel as (Fusarium solani). There are many species of Fusarium, including pathogens of plants & people, and even a slimy mass in bathroom drains. I must say that I truly miss this massive tree overlooking the Palomar College campus.

The pokeweed family also includes some unusual tropical vines, mostly native to the Caribbean region, Central and South America. Agdestis clematidea is a climbing vine native to Mexico and Guatemala. It grows from a huge gray tuber weighing up to 150 pounds (68 kg) and resembling a large granite boulder. Another interesting species called hoop vine (Trichostigma octandrum) in native to the Virgin Islands. Like a woody boa constrictor, it trails along the forest floor, ascending tropical trees and often forming tangled masses of writhing serpentine branches. It is essentially leafless except on new growth where leaves are produced that superficially resemble pokeweed. Hoop vine is used in basketry on the island of St. John, a rare art that is only practiced today by a few native islanders. The tightly woven baskets are made entirely from strips of hoop vine and are masterful works of art.

  Photos Of Hoop Vine On The Island Of St. John  

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