Ricin

[Major_Kong]

Is ricin a naturally occuring substance?

[Q.E.D]

Yes.

Ricin is a potent toxin derived from beans of the castor plant (Ricinus communis). The naturally occurring toxin is fairly easily removed from bean pulp remaining after castor oil extraction. Although ricin itself is not volatile, it may be formulated as a powder or an aerosol for intentional airborne dispersal. It is difficult to detect in human tissues or the environment. It can persist in the soil or environment for up to three day.

[Squink]

The Castor bean plant is commonly grown as an ornamental in the US. Its height, and large leaves (pics) make it a natural choice for garden backgrounds. The plant is winter hardy in the southwest, and is a common weed species in AZ, and So. Cal. It also makes frequent appearances in movies as a jungle-plant stand in.
The ricin containing seeds of the plant are also the source of commercially valuable castor bean oil. More on castor beans, castor bean oil, and ricin.

[Coriolanus]

NBC’s Jim Miklaszewski gleefully reported as fact what he was told by ‘sources’:

The sources said U.S. troops also discovered about 300 sacks of castor beans, which are used to make the deadly biological agent ricin, hidden in a warehouse in the town of al-Aziziyah, 50 miles southeast of Baghdad, the capital. The castor beans were inaccurately labeled as fertilizer.

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Thanks Jim. Good, um…journalism.

“The total world crop of castor beans is about a billion pounds per year,
yielding half that poundage of castor oil. The principal producing
countries are India and Brazil with lesser amounts from other Latin-
American countries, the West Indies, Africa, other parts of Asia, and
the United States. American manufacturers use about 40 percent of the
world’s crop and import nine-tenths of this. Castor Oil and its products
have hundreds of industrial uses and chemical research steadily adds
more. A substantial amount goes into paints, varnishes and lacquers.
A lipstick, a hair tonic, or a shampoo may contain over one-third
castor oil. Made into special lubricants for jet engines and racing cars,
it does not become stiff with cold nor unduly thin with heat. It is made
into plastics, soaps, waxes, hydraulic fluids and ink. During the war it
was stockpiled as a strategic material.”

http://newton.dep.anl.gov/natbltn/500-599/nb503.htm