Going Green: The Cryptobotanical Hypothesis
The examples of botanical presence in the UFO phenomenon are overwhelming. UFOs are often seen in forests, and in fields. They are even seen collecting soil samples in these places and even in the cities as well. This idea of "collecting soil samples" is often used to convey the idea of high strangeness-for some reason, the idea that aliens would be interested in soil has struck us, and it has stuck. Even some of our canned cultural aphorisms about UFOs, such as "why haven't aliens landed on the white house lawn," and "little green men from Mars," include botanical notions.
(Via The Anomalist.)