The Fabaceae family, also widely recognized as the pea family or legume family (Leguminosae), is a vast and economically significant group of flowering plants. If you’re familiar with the blossoms of peas or beans from your garden, you’ve already encountered a member of this family. Fabaceae plants are characterized by their unique, irregular flowers, typically composed of five petals arranged in a distinctive formation known as the “banner, wings, and keel,” as illustrated below.
Recognizing the “Banner, Wings, and Keel”
The hallmark of Fabaceae flowers lies in their petal arrangement. The “banner” is the uppermost petal, often broad and visually prominent, sometimes appearing as if two petals have fused. Flanking the banner are two “wing” petals. Lastly, the “keel” is formed by the two lowermost petals, which are often fused together, creating a boat-like shape. While the proportions of these parts can vary across different species within the Fabaceae Pea Family, the consistent presence of a banner, wings, and keel structure is a reliable indicator of family membership.
Another telltale sign of the fabaceae pea family is the presence of pea-like pods. These pods, which develop after flowering, are fruits that enclose the seeds and are a defining characteristic of legumes.
For a practical exercise in identification, observe a clover head in your lawn. Each clover head is actually a cluster of numerous tiny fabaceae pea family flowers. Upon closer inspection, you can discern the banner, wings, and keel in each miniature flower. As these flowers mature, each one will develop a small, pea-like pod – a detail you might not have noticed before!
The Expansive World of the Pea Family
The fabaceae pea family is one of the largest plant families globally, encompassing approximately 600 genera and 13,000 species. All members are descendants of an ancient pea flower that existed millions of years ago. Over vast stretches of time, fabaceae pea family members have adapted to a remarkable diversity of environments, ranging from low-growing clovers to towering trees that provide shade in urban landscapes.
Plant families of this size are often further categorized into subgroupings known as subfamilies and tribes, reflecting evolutionary relationships and shared characteristics.
Genera, Tribes, and Subfamilies: A Closer Look at Fabaceae Classification
Within the fabaceae pea family, closely related species are grouped into a “genus.” For instance, the clover genus, Trifolium (meaning “three-leaved”), includes about 300 distinct species worldwide. While each clover species is unique, they share fundamental clover characteristics, leading to their classification under the same genus, with individual species names such as T. arvense or T. pratense.
Comparing clovers to other members of the fabaceae pea family reveals that they share more similarities with alfalfa and sweet clover than with beans or caragana bushes. Consequently, plants like clover are categorized into the Clover tribe, while bean-like plants belong to the Bean tribe, and so on. Currently, there are eight recognized tribes within the Pea subfamily (also known as Papilionoideae). All these tribes within the Pea subfamily share the distinctive banner, wings, and keel flower structure. A significant portion of fabaceae pea family members found in northern latitudes belong to this Pea subfamily.
As you explore regions further south, you’ll encounter a greater diversity of species within the Pea subfamily, alongside plants from the Mimosa subfamily (Mimosoideae) and the Bird-of-Paradise-Tree or Senna subfamily (Caesalpinioideae). These latter subfamilies primarily include trees and shrubs, with some herbaceous members. While their flowers typically lack the classic banner, wings, and keel structure, many possess pinnate leaves (leaves divided into leaflets, similar to the illustration above) and the characteristic pea-like pods that split open along two seams. Each of these subfamilies exhibits enough unique traits to potentially be considered families in their own right. However, their underlying similarities are sufficient to classify them as subcategories within the overarching fabaceae pea family.
Edibility and Toxicity: A Spectrum within Fabaceae
The edibility of fabaceae pea family plants ranges from barely edible to slightly poisonous. Certain species contain toxic alkaloids, particularly concentrated in their seed coats. A well-known example is the tragic story of Christopher McCandless, who ventured into the Alaskan wilderness in 1992. McCandless consumed the roots of Hedysarum alpinum (wild sweet pea) and mistakenly assumed the seeds were also safe to eat. After consuming a large quantity of seeds over two weeks, he succumbed to starvation, despite continuing to eat. It is now believed that the seeds contained a toxic alkaloid similar to that found in locoweed, which inhibits an enzyme crucial for mammalian metabolism, preventing his body from utilizing the food he consumed. Even common garden peas, when consumed in excessive amounts, can lead to adverse effects like depression and nervous disorders. Therefore, while poisoning is possible with members of the fabaceae pea family, it generally requires significant consumption of specific plant parts.
Key Features of the Fabaceae Pea Family: “Banner, wings, and keel” flower structure. Pea-like pods, often accompanied by pinnate leaves.
Explore the Diversity: Pea Subfamily and Beyond
Let’s delve into some of the tribes within the Pea Subfamily and briefly touch upon the Mimosa and Caesalpinia subfamilies. Observe if you can identify the banner, wings, and keel in the flower images below.
Broom Tribe | Golden Pea Tribe | Hedysarum Tribe | Licorice Tribe | Clover Tribe | Trefoil Tribe | Pea Tribe | Mimosa Subfamily | Caesalpinia (Bird-of-Paradise Tree) Subfamily
For inquiries about image licensing or to report any inaccuracies, please e-mail Thomas J. Elpel.
Pea Subfamily: Broom Tribe
| Lupinus arbustus. Longspur Lupine. | Lupinus arbustus. Longspur Lupine. |
| Lupinus pusillus. Rusty Lupine. | Lupinus pusillus. Rusty Lupine. |
| Lupinus sp. Lupine. | Lupinus arboreus. Tree lupine, also known as yellow bush lupine. |
| Large leaf lupine: Lupinus polyphyllus. | Large leaf lupine: Lupinus polyphyllus. |
| Cytisus scoparius. Scotch Broom. | Cytisus scoparius. Scotch broom. |
| Ulex europaeus. Gorse. |  Foraging the Mountain West |
Pea Subfamily: Golden Pea Tribe
| Thermopsis montana. Golden Pea. | Thermopsis montana. Golden Pea. |
Pea Subfamily: Hedysarum Tribe
| Onobrychis viciifolia. Sainfoin. | Onobrychis viciifolia. Sainfoin. |
Pea Subfamily: Licorice Tribe
Pea Subfamily: Clover Tribe
| Trifolium repens. White clover. | Trifolium repens. White clover. |
| Trifolium haydenii. Bigleaf Clover. | Trifolium haydenii. Bigleaf Clover. |
| Trifolium pratense. Red Clover. | Trifolium wormskiodii. Springbank Clover. |
| Medicago sativa. Alfalfa. | Melilotus officinalis. Yellow Sweet Clover. |
Pea Subfamily: Trefoil Tribe
| Lotus corniculatus. Bird’s Foot Trefoil. | Lotus corniculatus. Bird’s Foot Trefoil. |
| Lotus corniculatus. Bird’s Foot Trefoil. | Lotus sp. Lotus. |
Pea Subfamily: Pea Tribe
| Hairy Vetch: Vicia villosa. | Hairy Vetch: Vicia villosa. |
Pea Family: Mimosa Subfamily
| Calliandra sp. Fairy Duster. | Calliandra sp. Fairy Duster. |
| ](https://hopspress.com/Books/Botany_in_a_Day.htm) |
Pea Family: Caesalpinia (Bird-of-Paradise Tree) Subfamily
| Cercis occidentalis. Western Redbud. | Cercis occidentalis. Western Redbud. |
| Cercidium microphyllum. Palo Verde Tree. | Cercidium microphyllum. Palo Verde Tree. |
| Parkinsonia florida. Blue Palo Verde. |
Explore More: Pea Family Pictures at PlantSystematics.org
| Foraging the Mountain WestStart feasting with Foraging the Mountain West |
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