One of the extraordinary details of biodiversity is the wealth of methods plants use to assure seed survival. Pods, casings, seed shapes and attachments for mobility are sufficiently individuated to enable botanists to identify many plants simply by looking at their seeds. Gravity, wind, water and weather all contribute to seed dispersal (even forest fire plays a part, loosening the seal that holds lodgepole-pine seeds tight in their cones). Animals, birds, and humans also impact the dispersal of seeds.
Seed Dispersal Overview
The methods plants use for seed dispersal fall into a small number of general classifications. A small number of plants contain structural mechanisms that scatter seeds. Others rely on air and water to disperse seeds, which are equipped with attachments resembling parachutes or wings. Still others need the agency of birds and animals to make certain that seeds are spread. Still others rely mainly on gravity and favorable ground conditions.
Impatiens capensis, popularly known as touch-me-not or jewelweed, bears seeds in pods that explode when touched. A few other plants rely on explosive pods, although more typically pods are so fragile that it is easy for seeds to fall; columbine is well known for rapidly deteriorating, paper-like pods that let seeds fall close to the plant. Whether seed holders explode or merely collapse, these plants tend to propagate in colonies, with new plants establishing close by.
A dazzling variety of wings, casings and bits of fluff that enable seeds to travel on the wind can be found on plants ranging from the majestic tulip tree to the humble dandelion. Severe windstorms can take seeds to new locations.
Animal- and Bird-Assisted Seeds
From mountain ash and nightshade to human-favored fruits, many fleshy-fruited and berried plants rely on consumption and excretion by birds and animals to disperse seeds. The close interdependence between plants and animals is illustrated by accidental and deliberate changes to the ecology of Mauritius.
Osage orange illustrates an example of disconnection between seed-maker and animal propagator. Some seeds are no longer viable when consumed by animals or birds; many tree nuts are too damaged to grow once eaten. Those buried or cached by squirrels and other animals retain the opportunity to establish as new plants.
Naturalists sometimes refer to burdock as "nature's velcro." Tiny spurs and weak stems let burdock seedpods attach easily to animal fur and human clothing. Cattail, cottonwood, thistle, and goatsbeard fluff enable seeds to travel via wind, fur or clothing.