writ­ten 6/1/2024, updat­ed 6/17/2024

Family Anacardiaceae

The Cashew/Sumac Fam­i­ly: Decid­u­ous trees and shrubs that pro­duce an oily or milky sap that can be high­ly poi­so­nous. Resin canals that exist in stems, leaves, and roots are found in all plants in the fam­i­ly. Their fruits are called dru­pes (stone fruit) where the fleshy part of the fruit sur­rounds a sin­gle shell which hous­es a seed

Com­mon Plants: Anac­ardi­um occi­den­tale (Cashew); Mangifera indi­ca (Man­go); Pista­cia vera (Pis­ta­chio); gen Cot­i­nus (Smoke Tree); gen Rhus (Sumac); gen Tox­i­co­den­dron (Lac­quer Tree, Poi­son Ivy, Poi­son Oak, Poi­son Sumac)

Note: The Tox­i­co­den­dron genus used to be lumped under Rhus. Tox­i­co — den­dron means tox­ic — tree.

Poison Ivy (Toxicodendron Radicans)

Native to most of the USA and south­ern Cana­da, it can be found in many types of envi­ron­ments from wet to dry, wood­lands, val­leys, clear­ings, road­sides, and back­yards. Poi­son ivy can exist as either a shrub (trail­ing, erect, or bushy) or a woody climb­ing vine with aer­i­al roots. It exhibits woody under­ground rhi­zomes. All aspects of the plant are poi­so­nous, con­tain­ing the per­sis­tent oily irri­tant, urush­i­ol. It is said that the vine ver­sion can cause 10–100 worse symp­toms than the shrub vari­ety

Note how the mid­dle leaf is set out longer than the oth­er 2 leaves. This is char­ac­ter­is­tic of Poi­son Ivy

Here you can see the Poi­son Ivy inter­spersed amongst oth­er plants and vines. The red are Poi­son Ivy, the pur­ple is Eng­lish Ivy, and the blue are Vir­ginia Creep­er

There’s a mas­sive Poi­son Ivy prob­lem at this house. Can you spot it amongst all the oth­er plants here?

The vine vari­ety

Poison Oak (Toxicodendron pubescens)

Low-grow­ing shrub native to Cen­tral and East­ern USA, it is found in dry, sandy loca­tions in wood­lands and thick­ets. The word pubes­cens is latin for “cov­ered in hair,” and the plant is named such owing to the fine hairs on stems and leaves. The plant roots are rhi­zomes and often form dense colonies. Yel­low­ish-green flow­ers appear in the spring­time, result­ing in green-tan­nish white dru­pes (fruit) by late spring. All aspects of the plant are poi­so­nous, con­tain­ing the per­sis­tent oily irri­tant, urush­i­ol.

SOURCE. You can see how they grow in clumps. Notice how the 2 leaves are more irreg­u­lar­ly lobed than the mid­dle leaf which, like poi­son ivy is set out a lit­tle

Poison Sumac (Toxicodendron vernix)

Decid­u­ous small tree or shrub, it is native to east­ern and cen­tral-east­ern USA, and east­ern Cana­da. There are many look-alike plants. Typ­i­cal­ly, Poi­son Sumac will not grow in clumps and since it prefers wet areas, will not be found in dry loca­tions, nor will it be com­mon­ly found along road­sides and fields. While it is the least like­ly of the big 3 to be exposed to, effects of the urush­i­ol from Poi­son Sumac tend to be more severe than its Poi­son Oak and Ivy rel­a­tives.

SOURCE

Red­dish stem, leaflets end­ing in a sin­gle leaflet, gray­ish brown bark

Urushiol

Urush­i­ol is an ole­o­resin (oil + resin) found in the sap of plants in the fam­i­ly Anac­ar­diaceae. It has potent aller­genic prop­er­ties that affect most humans on con­tact, caus­ing urush­i­ol-induced con­tact der­mati­tis. The chem­i­cal is per­sis­tent and can last for months on cloth­ing and gear unless cleaned thor­ough­ly with soap + water or rub­bing alco­hol.

Its irri­tat­ing effects are only applic­a­ble to humans and a few pri­mates. Oth­er ani­mals like dogs, cats, deer, birds, etc. are not affect­ed. In fact, birds, deer, cat­tle, goats, and oth­er wildlife ben­e­fit and feed from the plants.

Sci­en­cy Stuff

Toxicohedron Control — Before and After

Vine­gar Solu­tion

Reg­u­lar white vine­gar is only 5% acetic acid (and 95% water). You’re def­i­nite­ly going to want a high­er con­cen­tra­tion for this which can be found eas­i­ly in hard­ware stores up to 30% (usu­al­ly in the clean­ing and/or gar­den sec­tions), but you can get them even high­er online. I end­ed up buy­ing the 45% con­cen­trat­ed solu­tion (there’s even 75% or 95%). The gen­er­al for­mu­la is:

Results of Vine­gar

1 week apart

RoundUp and sim­i­lar prod­ucts

I real­ly dis­like using RoundUp, but I real­ly don’t want to mess with Poi­son Ivy espe­cial­ly giv­en my ter­ri­ble reac­tion to it. Ever since the issue with gly­cophos­phates and can­cer, RoundUp has changed their for­mu­la­tions away from gly­cophos­phates. Also, RoundUp does­n’t care if it rains (30 minute rain ready) or if it’s sun­ny out­side. It’s like­ly more sub­stan­tive than vine­gar, too. Just make sure you use eye pro­tec­tion and a mask

Active ingre­di­ents:

Results of RoundUp

I drenched the holy heck out of this plant with the RoundUp. It did not work as well as I thought it would

Fun Facts

The name urush­i­ol comes from the Japan­ese name for the lac­quer tree, urushi.

In 2016 an inter­na­tion­al group of sci­en­tists dis­cov­ered that a mol­e­cule found abun­dant­ly in human skin, CD1a, is respon­si­ble for the reac­tion of humans to urush­i­ol con­tact. CD1a is expressed by Langer­hans cells in the skin. Langer­hans cells are part of the immune sys­tem, and the CD1a mol­e­cule it pro­duces acts by pre­sent­ing lipid anti­gens to T‑cells. Since urush­i­ol is an ole­o­resin, the now acti­vat­ed T‑cell releas­es cytokines, caus­ing both inflam­ma­tion and itch­i­ness. Inter­leukin-33 was iso­lat­ed as a key cytokine in mouse stud­ies, along with its recep­tor ST2 on the small to medi­um dor­sal root gan­glion neu­rons. By block­ing the inter­leukin-33/ST2 (IL-33/ST2) sig­nal­ing path­way, relief from the hor­ri­ble itch­i­ness of urush­i­ol can be attained. Inter­est­ing­ly, IL-33 is also asso­ci­at­ed with eczema/atopic der­mati­tis and asth­ma. With this infor­ma­tion, a vac­cine is cur­rent­ly in the works to help desen­si­tize the body to urush­i­ol’s potent irri­tat­ing effects.

Urush­i­ol is found in some mem­bers of the Anac­ar­diaceae fam­i­ly includ­ing poi­son ivy, oak, and sumac, as well as man­go skins, cashews, and pis­ta­chios

Sources