Why Does a Plant's Fruit Help Disperse Seeds?

Overview

Plants have developed methods to ensure distribution of their seeds. Fruits may be fleshy, having plump tissues protecting the seeds, such as a peach or strawberry, or may be dry like peas or beans enclosed in a pod. Animals find nutrition in fruits, eating them for sustenance and passing the seeds in their excrement. Other fruits explosively propel their seeds or float in water, allowing prevailing currents to disperse them.

Fruit Types

Fruits of flowering plants (angiosperms) can be generalized into either fleshy or dry. Although not true fruits, the seeds of non-flowering plants (gymnosperms) like pines are dry, or those of cycads are surrounded by a juicy seed coat. Fleshy fruits develop as the tissues around the ovary swell as the seeds mature. The flesh often is colorful, nutritious, tasty and buoyant, all of which are advantageous to distributing the seeds. Prime examples include watermelon, currant, apple and holly. Dry fruits, when mature, can split open like a pod or remain within a hard casing like a nut. Additional appendages can occur on dry fruits that aid their dispersal, such as sticky hooks, cottony hairs or buoyant casing. Many dry fruits are nutritious to animals, too.

Wind

Fruits that are lightweight and have fibrous attachments or are shaped aerodynamically can be readily moved by the wind. The seeds of the maple (Acer) are affectionately called "helicopters" and known botanically as samaras. The papery keel attached to the fruit or seed spins as it falls more slowly due to its air resistance, traveling a greater distance from the mother plant. Dandelion (Taraxacum) and milkweed (Asclepias) shed their seeds with cottony fibers that also catch the breeze.

Water

Depending on their structures and densities, fruits may or may not float in water. Fleshy fruits may have limited buoyancy, and dry fruits have an advantage when being carried by moving water currents. The coconut (Cocos) fruit is dry and protects the hard seed inside, carrying it thousands of miles across the ocean. Lotus (Nelumbo) also disperses seeds by floating dry fruits.

Attachment

Fruits may have hooks, thorns, spurs or lengthy fibers that readily attach to hair, fur or clothing. Cocklebur (Xanthium) and some types of dryland grasses use this method.

Food Source

Animals gain sustenance from the nutrition found in the dry and fleshy fruits of plants. As the animals recognize the fruit or nut by scent, color or flavor, the fruits are ingested. The seeds within the fruits are usually protected by a thick seed coat that is unharmed when exposed to digestive acids. The seeds pass through the mammal or bird and are dropped in excrement a great distance from the mother plant.

Propulsion

Dry fruits can also project their seeds by explosively splitting. Many legume pods buckle as they dry and will snap open, launching seeds in the process.

Keywords: seed dispersal, floating fruits, animals dispersing seeds, fruits disperse seeds

About this Author

James Burghardt has written for The Public Garden, Docent Educator, numerous non-profit newsletters and for Learn2Grow.com's comprehensive plant database. He holds a Master's degree in Public Horticulture from the University of Delaware and studied horticulture and biology in Australia at Murdoch University and the University of Melbourne's Burnley College.