Plant symbiosis is a close relationship between a plant species and an organism of a different species. The relationships likely evolved in response to ecological pressures, such as to deter predators, grow taller, or make it easier to reproduce. Scientists have documented symbiosis between plants and fungi, plants and animals, and plants and other plants. Some symbiotic relationships benefit both species, while others help one of the species and harm the other.
Humans can harness the amazing connections between plants to improve the health and beauty of their gardens. By knowing how certain flowers keep bugs away from particular vegetables, or that different veggies planted together actually improve each other’s flavor, you can design an attractive garden that thrives on symbiosis.
Commensalism: A One-Sided Situation
Three main types of symbiotic relationships occur in nature. Commensalism describes symbiosis between two organisms in which one benefits and the other is neither harmed nor helped. These relationships are further classified into three categories. A commensal relationship in which one organism provides shelter for another, such as chickadees nesting in a tree cavity, is called inquilinism. Metabiosis describes commensalism between an organism that depends on another to provide a livable habitat; a plant needing microbes to create suitable soil for its growth is one example. A commensal relationship in which one species latches on to another for dispersal, like when a plant’s spiky seed pods stick to passing animals to be planted elsewhere, is called phoresy.
Parasitism: When Plants Get Needy
The symbiosis between a plant and a host organism, in which the host may be injured or eventually die, is called parasitism, and there are many familiar examples in the natural world. A parasitic plant typically derives nutrients from its host by way of a haustorium, a structure that penetrates the tissue of the other organism. Viscum album (European mistletoe) obtains water and nutrients from deciduous trees but also photosynthesizes its energy; it’s considered “hemiparasitic” for that reason. The world’s largest flower, the fully parasitic and charmingly named corpse lily (Rafflesia arnoldii), sucks up all of its sustenance from vines in the genus Tetrastigma.
Mutualism: It Takes Two to Tango
In mutualistic relationships, both parties benefit. These arrangements are probably what springs to mind when you think of symbiotic relationships between plants and other organisms. Bees and flowers are just one instance of mutualism: When bees gather flowers’ nectar for food, they get covered in pollen and spread it to other flowers to help the plants reproduce. Another example is zoochory, in which birds eat a plant’s fruit and then disperse its seeds in their droppings.
Symbiotic Plants for Your Garden
Also called “companion planting,” pairing mutually symbiotic plants in your garden can help them grow bigger and stay healthier without needing to use pesticides or other artificial means. Farmers have been planting certain vegetables together based on this principle for centuries. Corn, beans, and squash — aka the three sisters — help each other thrive; the cornstalks provide a trellis for the beans, the beans fix nitrogen in the soil for the other plants, and the squash’s big leaves offer shade and weed control. Other mutual pairs include tomatoes and asparagus, spinach and strawberries, and cucumbers and cabbage.
Friendly Flowers for Vegetable Plots
Many flowers and herbs, planted next to or between rows of vegetables, can help keep crops free of insect pests. Pairing marigolds with tomato plants is a tried-and-true way to avert nematodes and other bugs that gobble tomato leaves. Basil also repels insects, while bee balm, chives, and mint will boost tomatoes’ flavor. Garlic keeps pests off celery, lettuce, and roses, but it will hinder the growth of beans and peas. Edible nasturtiums repel aphids and beetles around brassicas, cucumbers, and lettuce, but may also offer cover for unwanted bugs. An online companion planting chart can help you design your symbiotic garden.