The nitrogen-fixing clade consists of four orders of flowering plants: Cucurbitales, Fabales, Fagales and Rosales. This subgroup of the rosids encompasses 28 families of trees, shrubs, vines and herbaceous perennials and annuals. The roots of many of the species host bacteria that fix nitrogen into compounds the plants can use.
The trees of this subgroup dominate many temperate forests. Cannabis, with the psychoactive drug tetrahydrocannabinol (THC), has been used recreationally and ceremonially for at least 2400 years, but was in cultivation at least 6000 years before that for its oils and for making fabric and rope. Cucumbers, melons and watermelons are cultivated around the globe. The Mediterranean diet around 6000 years ago included fava beans, lentils, chickpeas and other legumes. Chestnuts were spread throughout Europe by the ancient Romans. The apple (in the rose family) is the second-most-cultivated sweet fruit, after the grape (in the order Vitales, not in this clade).
From the glossary of botanical terms:
a plant species that completes its life cycle within a single year or growing season
attached close to the base (of a plant or an evolutionary tree diagram)
a vine that leans on, twines around or clings to other plants for vertical support
falling seasonally, as with bark, leaves or petals
not woody; usually green and soft in texture
of one sex; bearing only male or only female reproductive organs
hard and lignified; not herbaceous
Fabales is basal within the nitrogen-fixing clade. This clade, the COM clade and the order Zygophyllales constitute the fabids under the fourth Angiosperm Phylogeny Group (APG IV) system.
| Type genus and etymology | Total genera; global distribution | Description and uses | Order | Type genus images | |
|---|---|---|---|---|---|
| Anisophylleaceae (leechwood family) | Anisophyllea, from Greek for "unequal leaves" | 4 genera, mainly in the tropics | Shrubs and trees with unisexual flowers. Anisophyllea griffithii is sometimes harvested for timber. | Cucurbitales | |
| Apodanthaceae (stemsucker family) | Apodanthes, from Greek for "stalkless flowers" | 2 genera, scattered worldwide | Parasitic plants lacking chlorophyll. Typically, only the flowers are visible on the host's bark. | Cucurbitales | |
| Barbeyaceae (elm-olive family) | Barbeya, for William Barbey (1842–1914) | 1 genus, in forested slopes on either side of the Gulf of Aden | Unisexual trees | Rosales | |
| Begoniaceae (begonia family) | Begonia, for Michel Bégon (1638–1710), a French official and plant collector | 2 genera, mainly throughout the tropics, extending into the subtropics | Mostly perennial herbaceous succulents with unisexual flowers, with a few subshrubs and herbaceous plants up to 4m (13feet) tall. Some species grow on rocks, some on other plants. Many species are popular potted-plant ornamentals. | Cucurbitales | |
| Betulaceae (birch family) | Betula, from a Latin plant name | 6 genera, in the Northern Hemisphere and parts of South America and Southeast Asia | Deciduous shrubs and trees with unisexual flowers and loose bark, usually with lenticels, horizontal ruptures that allow gas exchange. The wood of birch and alder is used to make furniture and musical instruments. | Fagales | |
| Cannabaceae (hemp family) | Cannabis, from a Latin plant name | 9 genera, scattered worldwide | Shrubs, trees, vines and herbaceous plants with thin sap. Beer hops have been in cultivation since the 1200s. | Rosales | |
| Casuarinaceae (she-oak family) | Casuarina, from a Malaysian word for cassowary | 4 genera, in parts of Oceania, Southeast Asia and Madagascar | Evergreen trees and shrubs, unisexual or with unisexual flowers, with green branchlets and reduced leaves. Casuarina equisetifolia is planted to anchor beach sand. | Fagales | |
| Coriariaceae (tanner-bush family) | Coriaria, from Latin for "leather" | 1 genus, scattered worldwide | Shrubs and slightly woody herbaceous plants with nitrogen-fixing roots. The fruits are used for dyes. Most species are poisonous. | Cucurbitales | |
| Corynocarpaceae (cribwood family) | Corynocarpus, from Greek for "club fruit" | 1 genus, mostly in the southwestern Pacific | Evergreen trees and big shrubs. The trees have been used to construct canoes. | Cucurbitales | |
| Cucurbitaceae (cucumber family) | Cucurbita, from a Latin plant name | 101 genera, worldwide, especially in the tropics | Herbaceous and woody perennials, mostly vines. Butternut squash was domesticated in the Peruvian Andes over 9000 years ago. Cucumbers were cultivated in ancient Ur. | Cucurbitales | |
| Datiscaceae (durango-root family) | Datisca, from a Latin plant name | 1 genus, in central and southwest Asia, in and near California, and around the Mediterranean | Mostly unisexual herbaceous perennials with nitrogen-fixing bacteria. D. cannabina has been used as a dye in Asia. | Cucurbitales | |
| Dirachmaceae (rachman family) | Dirachma, from a Socotran plant name, possibly | 1 genus, in Socotra and Somalia | Trees and shrubs | Rosales | |
| Elaeagnaceae (oleaster family) | Elaeagnus, from a Greek plant name | 3 genera, mostly in the Northern Hemisphere, Southeast Asia and Queensland, Australia | Small trees and shrubs. Several species of Elaeagnus are cultivated as ornamentals. Hippophae rhamnoides has been used in jams and juices for centuries. The roots are generally nitrogen-fixing. | Rosales | |
| Fabaceae (pea family) | Vicia. Faba, an earlier synonym, is from a Latin plant name. | 780 genera, scattered worldwide | Also known as legumes. Trees, shrubs, vines and herbaceous plants. The roots are generally nitrogen-fixing. Staple foods include soybeans, peanuts, peas and various beans. Some species provide valuable gums, soaps and perfumes. | Fabales | |
| Fagaceae (beech family) | Fagus, from a Latin plant name | 8 genera, scattered in the tropics and the temperate Northern Hemisphere | Mainly trees with unisexual flowers. Edible chestnuts have been cultivated for thousands of years. Cork is harvested mainly from the cork oak. Wood from beech and oak trees is used in construction and carpentry. | Fagales | |
| Juglandaceae (walnut family) | Juglans, from a Latin plant name | 9 genera, mostly in parts of the Americas, Asia and Oceania. | Shrubs and trees, mostly with unisexual flowers. Trees with edible nuts include walnuts and pecans. | Fagales | |
| Moraceae (mulberry family) | Morus, from a Latin plant name | 48 genera, scattered worldwide | Shrubs, trees, climbers and herbaceous perennials, frequently with whitish sap. Some grow on other plants. The common fig was most likely already in cultivation more than 11,000 years ago. Breadfruit is a food crop in parts of Asia and the Pacific. | Rosales | |
| Myricaceae (bayberry family) | Myrica, from a Greek plant name | 3 genera, scattered worldwide | Evergreen shrubs and small trees, unisexual or with unisexual flowers. The roots are usually nitrogen-fixing. Chinese bayberry is grown commercially in China for its fruit. | Fagales | |
| Nothofagaceae (roble family) | Nothofagus, from Greek for "false", plus Fagus | 1 genus, in Oceania and southern South America | Shrubs and trees with unisexual flowers. The timber is used in carpentry. | Fagales | |
| Polygalaceae (milkwort family) | Polygala, from Greek and Latin plant names | 30 genera, scattered widely, except in polar regions | Herbaceous plants, vines, shrubs and trees, some up to 50m (160feet) tall. | Fabales | |
| Quillajaceae (soapbark-tree family) | Quillaja, from a Chilean plant name | 1 genus, in warmer regions of temperate South America | Evergreen trees with leathery leaves and foamy saponins in their bark | Fabales | |
| Rhamnaceae (buckthorn family) | Rhamnus, from Greek and Latin plant names | 63 genera, worldwide | Deciduous shrubs and trees, for the most part. Ziziphus jujuba and Z. mauritiana, similar to dates, are commercially grown. | Rosales | |
| Rosaceae (rose family) | Rosa, from a Latin plant name | 110 genera, worldwide | Trees, shrubs and herbaceous plants, frequently with spiny branches. The genus Rubus includes raspberries and blackberries. Prunus includes plums, peaches, cherries and almonds; domesticated almonds are found in Bronze Age archaeological sites in the Eastern Mediterranean. | Rosales | |
| Surianaceae (bay-cedar family) | Suriana, for Joseph Donat Surian (1650–1691), a French doctor, chemist and botanist | 5 genera, scattered worldwide in tropical, subtropical and warm-temperate zones | Shrubs and trees | Fabales | |
| Tetramelaceae (false hemp-tree family) | Tetrameles, from Greek for "four-part" (sepals) | 2 genera, in parts of Oceania and South and Southeast Asia | Tall unisexual trees with soft wood | Cucurbitales | |
| Ticodendraceae (tico-tree family) | Ticodendron, from Tico plus Greek for "tree" | 1 genus, in Central America and Mexico | Just one species of unisexual evergreen trees | Fagales | |
| Ulmaceae (elm family) | Ulmus, from a Latin plant name | 7 genera, mainly in the temperate Northern Hemisphere | Trees and shrubs with thin sap. Dutch elm disease killed almost all of the elms in North America and Europe in the 20th century. Disease-resistant elms have been difficult to propagate. | Rosales | |
| Urticaceae (nettle family) | Urtica, from a Latin plant name | 60 genera, worldwide | Shrubs, trees, woody vines and herbaceous plants, some growing on other plants, and some with stinging hairs. Ramie (Boehmeria nivea) is grown in East Asia for its long, strong fibrous stalks. | Rosales | |