Plant Families | GEOG 3: Food and the Future Environment

Plants that have similar flowers, reproductive structures, other characteristics, and are evolutionarily related, are grouped into plant families (See Figure 2). Species in the same plant family tend to have similar growth characteristics, nutrient needs, and often the same pests (pathogens, herbivores). Planting crops from different plant families on a farm and the landscape; and rotating crops of different plant families over time can interrupt the crop pest life cycles, particularly insect pests, and pathogens, and reduce yield losses due to pests. Increasing plant family diversity can also provide other agrobiodiversity benefits including, diverse seasonal growth and adaptation to weather stresses such as frosts, and drought; different soil nutrient needs, as well as producing diverse foods that provide for human nutritional needs.

Plant family tree — Figure 6.2.1: The Plant Family Tree

Read this summary of the major world food crop plant families and the value of knowing what family plants are in, The Organic Way - Plant Families, then consider these questions.

What plants are your five favorite foods produced from?
What plant families are they in?
Are they annuals or perennials?

The Fabaceae/Leguminosae, commonly called the Legume plant family, is important for soil nitrogen management in agriculture and for soil, human and animal nutrition. Legume plants can form a mutualistic, symbiotic association with Rhizobium bacteria which inhabit legume roots in small growths or nodules in the roots (seed images in the video listed below). The rhizobia bacteria have enzymes that can take up nitrogen from the atmosphere and they share the “fixed nitrogen” with their legume host plant. Nitrogen is an important nutrient for the plants and animals, it is a critical element in amino acids and proteins, genetic material and many other important plant and animal compounds. Legume grains crops, also called pulses are high in protein, such as many species of beans, lentils, peas, and peanuts. Most of their plant nitrogen is harvested in grain, although there is some in crop residues that can increase soil nitrogen content. Perennial legume crops are typically grown as forage crops for their high protein for animals. Because they allocate a large portion of their growth to vegetative plant parts and storage organs, perennial legumes also return a significant quantity of nitrogen to the soil, enhancing soil fertility for non-legumes crops grown in association or in rotation with legumes.

Watch the following NRCS video about legumes and legume research.

The Science of Soil Health: Understanding the Value of Legumes and Nitrogen-Fixing Microbes (2:30)

Transcript: The Science of Soil Health: Understanding the Value of Legumes and Nitrogen-Fixing Microbes (2:30)

Legumes and cash and cover crops use natural symbiotic relationships with soil microbes to get nitrogen into the soil. NC State University's Dr. Julie Grossman is working to provide farmers with new insights on how to harness this resource. My work really involves looking at legumes to try to figure out how we can really make them make them the most efficient nitrogen source we possibly can, by looking at the microbial component of the legume-rhizobia symbiosis. And we work a lot with organic farmers simply because right now, that's those are the farmers who are really interested in using legumes for nitrogen supply. As nitrogen prices go up we're gonna need to turn to some of these alternative processes such as nitrogen fixation. And when that happens, we need to be able to hit the ground running. We can't say, “okay now we're gonna start doing the research.” We really want to get to know how, when you take a bacteria, a strain of bacteria, and you look at its DNA, how does it differ from other strains of bacteria. Because you can have some that are very high performers and they fix a lot of nitrogen and you can have others that don't really do a heck of a lot for the plant. In my mind, what would really help the farmers is trying to understand the tools they can use as farmers to help increase nutrient supply to their crop plants. So try to figure out how much nitrogen is supplied when they put a legume in the soil and let it decompose, how that is released when it's released, how we can get more nitrogen into the legume by enhancing the fixation ability of the microbes. So all these little pieces will help us be able to help farmers develop their own research, their own experimentation, so they don't need to rely on the recipes. They can say, “Oh, I know that if I can calculate a square meter of legume biomass and I can calculate how much I have and how much nitrogen is in that square, I can then figure out on my whole field, how much nitrogen is being added through this legume to my soil.” And so those are the kinds of things I really want to give to farmers, in terms of having them understand how they can control their own biological process, in their fields on their own, and not have to rely on recipes.

Credit: TheUSDANRCS. "The Science of Soil Health: Understanding the Value of Legumes and Nitrogen-Fixing Microbes." YouTube. May 30, 2011.