7.2.1: 1 Plant Families

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.

Figure 6.2.1.: The Plant Family Tree. Credit: The U. S. Botanic Garden and the National Museum of Natural History, Department of Botany, Smithsonian Institution.

Click for a text description of Figure 6.2.1.

The Plant Family Tree Ancestral Green Algae

1. Modern Green Algae - single and multicellular algae
   1. Volvox Spirogyra
2. Seedless Non-vascular - plants with no veins and no seeds
   1. Liverworts
   2. True Mosses
3. Seedless Vascular - plants with veins and NO seeds
   1. Selaginella
   2. Quillworts
   3. Club Mosses
   4. Whisk Ferns
   5. Adder's Tongue
   6. Water Ferns
   7. Royal Ferns
   8. Horsetails
   9. Climbing Ferns
   10. Tree Ferns
   11. Common Fern
4. Gymnosperms - Plants with cones
   1. Ephedra
   2. Welwitschia
   3. Firs
   4. Pines
   5. Ginkgo
   6. Cycad
   7. Yew
   8. Sequoia
   9. Cypress
   10. Podocarpus
   11. Monkey Puzzle
5. Angiosperms - Flowering Plants
   1. Dicots
      1. Euphorbs
      2. Violets
      3. Willows
      4. Mustard
      5. Papaya
      6. Cacao
      7. Mallow
      8. Maples
      9. sumacs
      10. Citrus
      11. Roses
      12. Elms
      13. Hopes
      14. Mulberries/figs
      15. Beans
      16. Begonias
      17. Cucumbers
      18. Oaks
      19. Walnuts
      20. Birch
      21. Coffee
      22. Milkweeds
      23. Gentians
      24. Morning Glories
      25. Tomatoes
      26. Scrophs/Snapdragons
      27. African Violets
      28. Holly
      29. Olive
      30. Mints/Verbena
      31. Ginseng
      32. Carrots
      33. Sunflowers
      34. Pawpaw
      35. Magnolia
      36. Laurel
      37. Pepper
      38. Poppies
      39. Grapes
      40. Buttercup
      41. Eucalyptus
      42. Evening Primrose
      43. Geraniums
      44. Sedum
      45. Peonies
      46. Currants
      47. Sycamore
      48. Star Anise
      49. Water Lilies
      50. Sundew
      51. Mistletoe
      52. Carnations
      53. Beets
      54. Cacti
      55. Portulaca
      56. Blueberries
      57. Impatiens
   2. Monocots
      1. Amborella
      2. Aroids
      3. Yams
      4. Lilles
      5. Iris
      6. Palms
      7. Pineapple
      8. Sedges
      9. Dayflowers
      10. Bananas
      11. Gingers
      12. Cannas
      13. Grasses
      14. Orchids
      15. Asparagus
      16. Agave
      17. Amaryllis
      18. Onions
      19. Daylillies
      20. Aloe

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.

1. What plants are your five favorite foods produced from?
2. What plant families are they in?
3. 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.

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

Click for a transcript of the Science of Soil Health video.

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.

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Knowledge Check (flashcard)

Consider how you would answer the question on the card below. Click "Turn" to see the correct answer on the reverse side of the card.

Card 1:

Front: What are some of the benefits of including legumes in a crop rotation?

Back: Legumes return some nitrogen to the soil, particularly perennial legumes that allocate a proportion of their resources to vegetative growth (ex. roots and shoots) and storage organs. Legumes also produce a crop that is high in protein, whether it is a high protein annual grain legume (also called a pulse) or perennial crop.