Post by madyaas on Sept 18, 2007 1:58:44 GMT -5
Urushi, as we know, comes from the lacquer tree, Toxicodendron verniciflua. This tree was formerly named within the genus Rhus, but has been moved over to Toxicodendron (primarily due to resin channels found within the fruit, not found in Rhus). Those of us in North America know members of this family as poison oak and poison ivy.
The Lacquer Tree's latin name is Toxicodendron verniciflua. Toxicodendron meaning roughly "toxic tree", verniciflua meaning "lacquered" or referring to lacquer, from what I've found.
All of the members of Toxicodendron are within the anacardiaceae (cashew) family. This family includes plants like cashews (which have to be roasted to make safe to eat), mangoes, which can give a skin rash in sensitive people who suck the pulp from the skin of the fruit, and rengas (Gluta renghas), said to have incredibly toxic (or at least potent) sap. Toxicodendron is primarily found within North America, China, Japan, and Malaysia.
Many of these members of Toxicodendron have beautiful fall foliage. Toxicodendron diversilobum (Poison Oak) has such beautiful fall foliage that it can compete in color with the best Japanese Maples or eastern Maples. I've actually thought about growing it as a bonsai specifically for this purpose (with minimal handling and with gloves, I am not allergic to it). It will often show reds and pinks throughout the year. When it was first discovered, Poison Oak (T. diversilobum) was brought back to England and grown in gardens because in shade it will climb whatever support it finds, and because of its aforementioned fall color.
Members of Toxicodendron contain a sticky terpene oleoresin sap which polymerizes into a hard black lacquer. This is the urushi which is used for lacquer ware in China and Japan. The Pomo and other Indians of the western US often used it for dyeing materials for their baskets black (and it lasts, just like urushi). The sap must be handled carefully, or a very painful reaction can occur. However, many tribes used it to cure things like warts, and soap lily (Chlorogalum) bulbs were wrapped in the leaves and baked. The urushiol in the sap can also be carried in fires, and this is why western wildfires can be so hazardous smoke wise -- it gets into the air and can travel miles from the fire, spreading misery (mostly as microdroplets in smoke, or bound to ash).
Urushiol binds to cell membranes. It is this which causes the inflammation, as it tags the cell it is attached and causes the immune system to respond. Urushiol is such a strong allergen that one millionth of an ounce is enough to cause a reaction. A pinhead's worth is enough to cause a reaction in 500 sensitive people! Urushiol is so stable, herbarium specimens over a century old can still cause reactions.
Objects covered in urushi can cause allergenic reactions in sensitive people, since polymerization of the sap doesn't destroy the molecule. Aside from urushi, Ginkgo biloba seeds also contain urushiols, and some people are allergic to touching the smelly, soft seed coats (the soft outer part of the ginkgo nut is not fruit flesh). Some members of the protea family also contain urushiols (which suggests to me that the chemical is an ancient one, as both Gingko and Proteaceae are ancient families). Mangos as well can cause a reaction, being members of the Anacardiaceae family.
Still, urushi is beautiful stuff, and it amazes me that despite its toxicity and allergenic properties, it continued to be used for thousands of years. If you would like to know more about the science behind urushiol, this is a fascinating page, and where I obtained a lot of the information presented in this post: waynesword.palomar.edu/ww0802.htm)
The Lacquer Tree's latin name is Toxicodendron verniciflua. Toxicodendron meaning roughly "toxic tree", verniciflua meaning "lacquered" or referring to lacquer, from what I've found.
All of the members of Toxicodendron are within the anacardiaceae (cashew) family. This family includes plants like cashews (which have to be roasted to make safe to eat), mangoes, which can give a skin rash in sensitive people who suck the pulp from the skin of the fruit, and rengas (Gluta renghas), said to have incredibly toxic (or at least potent) sap. Toxicodendron is primarily found within North America, China, Japan, and Malaysia.
Many of these members of Toxicodendron have beautiful fall foliage. Toxicodendron diversilobum (Poison Oak) has such beautiful fall foliage that it can compete in color with the best Japanese Maples or eastern Maples. I've actually thought about growing it as a bonsai specifically for this purpose (with minimal handling and with gloves, I am not allergic to it). It will often show reds and pinks throughout the year. When it was first discovered, Poison Oak (T. diversilobum) was brought back to England and grown in gardens because in shade it will climb whatever support it finds, and because of its aforementioned fall color.
Members of Toxicodendron contain a sticky terpene oleoresin sap which polymerizes into a hard black lacquer. This is the urushi which is used for lacquer ware in China and Japan. The Pomo and other Indians of the western US often used it for dyeing materials for their baskets black (and it lasts, just like urushi). The sap must be handled carefully, or a very painful reaction can occur. However, many tribes used it to cure things like warts, and soap lily (Chlorogalum) bulbs were wrapped in the leaves and baked. The urushiol in the sap can also be carried in fires, and this is why western wildfires can be so hazardous smoke wise -- it gets into the air and can travel miles from the fire, spreading misery (mostly as microdroplets in smoke, or bound to ash).
Urushiol binds to cell membranes. It is this which causes the inflammation, as it tags the cell it is attached and causes the immune system to respond. Urushiol is such a strong allergen that one millionth of an ounce is enough to cause a reaction. A pinhead's worth is enough to cause a reaction in 500 sensitive people! Urushiol is so stable, herbarium specimens over a century old can still cause reactions.
Objects covered in urushi can cause allergenic reactions in sensitive people, since polymerization of the sap doesn't destroy the molecule. Aside from urushi, Ginkgo biloba seeds also contain urushiols, and some people are allergic to touching the smelly, soft seed coats (the soft outer part of the ginkgo nut is not fruit flesh). Some members of the protea family also contain urushiols (which suggests to me that the chemical is an ancient one, as both Gingko and Proteaceae are ancient families). Mangos as well can cause a reaction, being members of the Anacardiaceae family.
Still, urushi is beautiful stuff, and it amazes me that despite its toxicity and allergenic properties, it continued to be used for thousands of years. If you would like to know more about the science behind urushiol, this is a fascinating page, and where I obtained a lot of the information presented in this post: waynesword.palomar.edu/ww0802.htm)