Walnut trees are not particularly well suited to smaller urban gardens. Both the fallen leaves and the roots secrete a substance called juglone which kills many popular garden plants, such as tomato, apple and birch; all walnuts produce juglone, but Black Walnut produces larger amounts than other species. Juglone appears to be one of the walnut's primary defense mechanisms against potential competitors for resources (water, nutrients and sunlight), and its effects are felt most strongly inside the tree's "drip line" (the circle around the tree marked by the horizontal distance of its outermost branches). However, even plants at a seemingly great distance outside the drip line can be affected, and juglone can linger in the soil for many years even after a walnut is removed as its roots slowly decompose and release juglone into the soil.

Christopher Columbus was one of the first Europeans to encounter chili peppers, and called them "peppers" because of their similarity in taste (though not in appearance) with the Old World peppers of the Piper genus(black pepper). Columbus was keen to prove (incorrectly) that he had in fact opened a new direct nautical route to Asia, contrary to reality and the expert consensus of the time, and it has been speculated that he was therefore inclined to denote these new substances "pepper" in order to associate them with the known Asian spice

The chemical compound capsaicin is the active component of chili peppers. It is an irritant for mammals, including humans, and produces a sensation of burning in any tissue it comes in contact with. The seeds of Capsicum plants are predominantly dispersed by birds, in which capsaicin has analgesic properties rather than acting as an irritant. Chili pepper seeds consumed by birds pass through the digestive tract unharmed, whereas those consumed by mammals do not germinate at all. The presence of capsaicin in the fruits therefore protects them from being consumed by mammals, which wouldn't provide any benefit to the plant, while allowing them to be eaten by its preferred seed carriers.

All the aspens (including White Poplar) typically grow in large colonies derived from a single seedling, and spread by means of root suckers; new stems in the colony may sprout as much as 30–40 meters from the parent tree. Each tree will only live for 40–150 years above ground. The root system is long-lived, in some cases for many thousands of years, sending up new trunks as the older ones die off above ground. One colony in the state of Utah, nicknamed Pando, is claimed to be 80,000 years old, making it possibly the oldest living colony. Some experts call it the largest organism in the world, by mass or volume. It covers 43 hectares and is estimated to weigh 6,600 tons.

Seaweeds are commonly described as plants, but biologists do not consider them true Plantae. They are actually made up of multicellular algae and are classified into brown, red, and green algae based on their pigment composition.