Flowering plants, or angiosperms (from the Greek, meaning encapsulated seed), make up the largest, most diverse group of terrestrial flora. The Fabaceae (Leguminosae) family, also called the legume family, is the third largest group of flowering plants, after Orchidaceae and Asteraceae, with over 700 genera and about 20,000 species. It is also one of the most economically important families, including crops such as beans, peas, alfalfa, and peanuts. The name Fabaceae is derived from the Latin, faba, referring to the broad bean (Vicia faba), a popular legume in Europe. One of the defining characteristics of the Fabaceae is the production of bean-like seeds enclosed in a pod (a legume). Many species also have the ability to fix nitrogen by means of symbiosis with rhizobia bacteria, which live in root nodules and convert nitrogen gas from the air into nitrate or ammonia, forms of nitrogen that plants can use directly. The majority of legumes are herbaceous species, both annual and perennial, but there are also hundreds of tree, shrub and vine species of legumes, inhabiting many different environments throughout the world. Many of these make excellent ornamentals for the human environment, and some have become staples of the nursery industry, such as honeylocust (Gleditsia triacanthos f. inermis). In this article I will describe some of the other tree species, hardy to the northeastern United States, which make excellent ornamental and shade trees.

Redbud

One of the most popular small flowering trees is the redbud (Cercis canadensis). With its profusion of small pink pea-like flowers in May before the leaves emerge, the redbud is an effective specimen tree or in a grouping, especially in a naturalized setting. It can tolerate full sun or partial shade, and will even thrive under black walnuts (Juglans nigra). It is highly adaptable to all soil types, except swampy soils. It is, however, prone to mechanical injury such as crotch splitting from heavy snow loads and wind. It is also subject to Verticillium wilt and treehopper damage, as well as some cankers. Unlike most of the Fabaceae family, redbuds have simple heart-shaped leaves, which emerge as the flowers begin to fade, starting out a reddish-purple and changing to deep, lustrous green. Fall color is yellowish green, occasionally a good yellow, but is not reliable. The rosy pink pea-like flowers emerge from reddish-purple buds in clusters of 4 to 8 along the branches, and sometimes along the main trunks. From the flowers emerge small pods, containing two or three bean-like seeds. The pods turn dark brown in the fall and can persist through most of the winter. On mature trees the bark is a beautiful shaggy reddish brown and exfoliates in long shreds. Redbuds can grow to about 30' in height and are often multi-trunked, or low branching, often with gradually ascending branches forming a flat-topped rounded crown as wide as tall. Small branches and twigs tend to zigzag. Although hardy to at least Zone 4, redbuds have such a wide native range, from New Jersey to Florida, and west to Texas and northern Mexico, that hardiness is determined by provenance. A tree grown in Florida will probably not produce seed hardy to New York.

There are now over 30 cultivars of redbud in the trade, only a few of which are truly different, and many of them are not as hardy as the species, having been discovered in southern states such as Tennessee. Perhaps the most common cultivar is 'Forest Pansy', a purple-leaved variety, discovered in Tennessee in 1947. New foliage emerges a deep red-purple, changing to a more subdued purple by summer. In shaded situations the leaves are often green in summer, while full sun seems to maintain a better purple. I have seen a number of 'Forest Pansy' specimens around the Rochester area, but they don't seem to be as hardy as the species and are often short-lived. 'Hearts of Gold' is a yellow-leaved variety, which will turn green if water-stressed in summer. There are three weeping forms of redbud. The most common one is Lavender Twist(TM), 'Covey', hardy to Zone 5, propagated and patented by Tim Brotzman of Ohio. The original plant was grown in Westfield, New York, by Connie Covey, and is now only 5' tall and 8' wide after 30 years. Most specimens of Lavender Twist are staked to about 6' high. Another weeper is 'Cascading Hearts', which apparently has fuller leaf coverage than Lavender Twist. There is a newly developed weeping form, called 'Ruby Falls', a hybrid between 'Covey' and 'Forest Pansy', with red-purple leaves. There are a few variegated forms, such as 'Silver Cloud' and 'Floating Clouds', with white-speckled leaves.

There are a few dwarf cultivars of redbud. 'Ace of Hearts' is a shrubby type to about 12' with shiny green leaves and abundant flowers. 'Little Woody' is similar with thick rugose leaves on a dense shrubby form and deeper pink flowers. Paul Woody of North Carolina introduced both of these varieties. 'Tom Thumb' grows to about 6' by 6' in an upright spreading form.

Redbuds also come with white flowers, often called "whitebud". 'Alba' is a white-flowered form, whose new leaves lack the reddish tint of the species. A more cold-hardy type is 'Royal White', selected for larger white flowers at the University of Illinois. 'Texas White' is a form of the subspecies texensis, with leathery leaves and wavy margins, and is hardy to about Zone 6.

As with many North American species, China also has its redbud, Cercis chinensis. This is an upright multi-stemmed shrub to about 8 to 10'. The flowers emerge at the same time as C. canadensis, but tend to be more profuse, lining the branches and the main stems. Although not as hardy as the American species (Zone 6), the Chinese redbud is more showy.

There is a redbud for just about every garden situation. It is one of the most beautiful of the native trees. It is also quite a prolific seeder, and once established will produce many offspring.

American Yellowwood

Another native American tree of the bean family is the American Yellowwood, Cladrastis kentukea (C. lutea). A native of North Carolina, Kentucky and Tennessee, with scatterings in the midwestern states, this tree inhabits limestone soils on river valleys and ridges along streams. It is rare in the wild and even rarer in cultivation. It was discovered and recorded in Tennessee in the late 18th century by Andre Michaux, the Royal Botanist to Louis XVI of France, who collected seeds and sample specimens to be sent back to Paris. At first it was named Virgilia lutea, being similar to several southern African species of Virgilia, also members of the Fabaceae (one of its common names today is Virgilia). Later it was named Sophora lutea (lutea means yellow). In the early 19th century it was recognized by the French biologist Rafinesque as a distinct genus and named Cladrastis fragrans. Later it was renamed C. lutea and finally C. kentukea.

Although native to the southern states it is hardy to Zone 4. Usually low-branching or multi-trunked, Yellowwood can grow to 50', producing a broad, rounded crown; it can grow quite fast with adequate water. The trunk is very smooth and light gray, reminiscent of beech. Small twigs are dark brown and tend to zigzag between buds. The heartwood is bright yellow, hence the common name. The alternate, odd-pinnately compound leaves emerge yellowish-green, becoming bright green upon maturity. There are usually 7 leaflets, broadly ovate, with the terminal leaflet the largest. The overall leaf is about 8 to 12" long, and the petiole has an enlarged base enclosing the bud. The fall color is usually bright golden yellow, and after the leaflets fall, the yellow petiole (rachis) generally remains over much of the winter covering the buds. In early June, after the leaves are almost fully expanded, terminal pendulous panicles of white pea-like flowers emerge, superficially reminiscent of another member of the Fabaceae, black locust (Robinia pseudoacacia), but much larger to about 14" and showier. The flowers are fragrant, especially at night, and an excellent source of nectar frequented by bees, and presumably moths. Unfortunately, the trees generally flower every other year, and not until they are at least about 15' tall. After the flowers fade, seedpods develop. These are 2 to 4" long and sparsely distributed along the panicles. They are thin and contain usually one, or occasionally two, small light brown bean-shaped seeds. The seeds are very hard-coated and require scarification to germinate.

Very few problems plague the yellowwood, although Verticillium wilt has been reported, and brittle wood and tight crotches can result in mechanical damage. The botanical name Cladrastis is derived from the Greek words for branch (klados) and fragile (thraustos). It is a very adaptable species, tolerant of a wide range of soils, including high pH as well as acid. It can also grow in the vicinity of black walnuts without effect. Chlorosis can develop sometimes, and is readily remedied with applications of calcium. Full sun to part shade is preferred, and given its brittle wood, a non-windy site is probably best. It is a profuse bleeder and should not be pruned in winter or spring, but only in the summer. Flowing sap can often be seen in early spring, from winter injuries or insect activity, but rarely creates a problem.

Very few cultivars of yellowwood have been selected to date, probably because of the trees relative obscurity in the trade. There is a beautiful pink-flowered form, 'Perkins Pink', originally from the Perkins Institute for the Blind in Massachusetts.

The American Yellowwood is a superb tree and should be used more frequently. Unfortunately, it remains in obscurity for unknown reasons, perhaps because young, containerized seedlings tend to be somewhat slow to start and gawky, making them a hard sell. But once planted in the ground the tree will grow quite rapidly into a superb flowering specimen, worthy of any garden. Specimens of Yellowwood, including 'Perkins Pink' can be seen at Holmes Hollow Farm in Victor, NY.

Kentucky Coffeetree

Native from New York to Tennessee and west to Minnesota and Oklahoma, the Kentucky Coffeetree (Gymnocladus dioicus) makes a superb choice for parks and large open areas in Zones 3 to 7. Growing at a medium rate, it can mature at about 70' tall with a 50' spread. Rather gangly in youth, the trunk grows straight to about 10' before branching. The crown remains fairly open creating a light shade. The bipinnately compound leaves emerge quite late in May and can reach lengths of 3'. Emerging leaflets have a reddish tinge, changing to blue-green in summer. Fall color is sometimes a good yellow, but leaflets abscise early, leaving the yellow rachis, which can persist well into winter. The name Gymnocladus means naked branch, and probably refers to the trees long season without foliage. In early June greenish-white fragrant flowers emerge in 8" long panicles, but are rarely noticed, except by pollinating insects. As the specific epithet suggests, the flowers are mostly dioecious, and flowers on the male trees are somewhat smaller, although occasionally a tree will have polygamous flowers also. Developing from the female flowers come very large dark brown leathery pods, 5 to 10" long and up to 2" wide, containing several very hard dark brown round seeds embedded in a sweet, sticky pulp. The pulp contains a poisonous alkaloid, cytisine, which has been known to be toxic to cattle. The seeds mature in October, but the pods often remain on the tree for much of the winter. The seeds were once roasted and ground as a substitute for coffee.

Kentucky Coffeetree is very adaptable to most soil conditions, including high pH, drought and urban conditions. It is easy to grow, given plenty of sun, and makes a good shade tree, while still allowing underplantings. Because of the mess associated with falling fruit and the toxic potential of such, a few male cultivars have been developed in the Midwest, most notable of which are 'Prairie Titan' and 'Stately Manor', although none are commonly available. Personally, I regard the fruit as a positive feature of the tree, which makes it rather unique. A fine collection of Coffeetrees can be seen at the Buffalo and Erie County Botanical Gardens.

Locust

There are many other native American species of Fabaceae, most of which grow around the Gulf of Mexico and the Southwest, such as Acacias, Blackbeads, Paloverdes and Mesquites. Two species, which are common in our area, are Honeylocust (Gleditsia triacanthos var. inermis), and Black Locust (Robinia pseudoacacia). Honeylocust is native from Pennsylvania to Nebraska and Texas, but most wild trees sport very large sharp thorns around the trunks and branches. A thornless variety of Honeylocust was extensively planted after the demise of the American Elm, as it appeared to be a tough tree, easy to grow and not subject to disease and insect problems. Moreover, the small leaflets allowed for a filtered shade and reduced cleanup chores. However, any time one species is favored over diversity, problems inevitably follow. Such is the case with Honeylocust, which are now plagued by leaf spot, witches brooms, cankers, borers, webworm, pod gall, spider mites, rust and mildew. I would recommend against planting any more Honeylocust.

The Black Locust (Robinia pseudoacacia) is native from Pennsylvania to Georgia and west to Iowa and Oklahoma, but has been extensively planted elsewhere and is firmly established in western New York, where it freely reseeds itself. The hard wood is extremely durable and is used for fence posts, and the white flowers are an excellent source of nectar for honeybees. Its habit is very upright with a narrow crown, and it tends to form thickets by reseeding and root suckers, which are very spiny. With age the trees tend to be broken by storms and develop a rather scraggly look. Altogether, it's a very unkempt tree, which I don't recommend planting. However, there are a few cultivars that might be worth a second look. 'Frisia' is a golden foliage form, very popular in Europe. 'Purple Crown' is a vigorous, adaptable variety with purple flowers, probably a hybrid with R. hispida. 'Purple Robe' is a smaller tree to about 30' with rosy-red flowers.

Amur Maackia

As one might expect, Asia also has its share of bean trees, very few of which have found their way into American gardens. Two of these are very adaptable to the climate and soils of western New York, and should be given more consideration.

A close relative of the American Yellowwood, the Amur Maackia (Maackia amurensis) is a native of Manchuria and Korea. Named after the Russian naturalist, Richard Maack, the Maackia is a small tree to about 25' with an upright spreading, rounded canopy. Hardy to Zone 4, it is perfectly adapted to conditions in the northeast, tolerant of a range of soils, including compacted and high pH, and has the ability to fix atmospheric nitrogen. Insects or diseases do not bother it to any degree. Its adaptability and small stature makes it a good street tree in urban conditions. The large dark brown, shiny buds open in May as the silvery gray-green leaves unfurl, a very attractive sight. The alternate leaves are odd-pinnately compound, with opposite leaflets, which emerge with a fine silvery pubescence and turn a glabrous bright green upon full extension. There is no significant fall color to the leaves, most falling green. Like most of the Fabaceae, the rachis remains attached after the leaflets fall, but unlike the Yellowwood, the Maackia rachis does not cover the bud. In late June to early July stiff, erect racemes of white flowers emerge, which smell like new-mown grass. They attract pollinators; in my nursery I noticed a small, 6' Maackia whose flowers were literally covered in swarms of large, black bees of an unidentified species I have never seen on any other plants. Most of the flowers produce 2 to 3" pods, each containing 2 or 3 hard-coated seeds. The bark on the trunk has a golden hue with some exfoliation, quite attractive.

The Maackia is virtually unknown in gardens and many arboreta, but it makes a very attractive, small tree for the suburban lot or street situation. The summer flowers are a bonus, and the peeling bark adds to the attraction. This should be on every gardener's wish list.

Scholar-tree

The Scholar-tree or Japanese Pagoda tree (Styphnolobium japonicum; formerly Sophora japonica) is a native of China and Korea, hardy to Zone 4. It makes a very fine specimen, growing upright to about 50' with an equal spread. It is very tolerant of pollution, and drought, and therefore makes for a good street tree in urban conditions. The young stems and branches are bright green and remain green for about 5 years, before developing a rather crusty-looking light tan bark. The bark on older trunks is reminiscent of black locust with long vertical ridges of light gray-brown. The leaves are alternate odd-pinnately compound, a bright green with no appreciable fall color. In late July or August creamy white, slightly fragrant pea-like flowers emerge in 6" to 12" long terminal panicles, making for quite a good show and lasting for a couple of weeks. After the flowers fade 3" long green pods develop, containing 2 or 3 seeds. Unlike the pods of other Fabaceae, these are constricted around each seed, so that the number of seeds per pod is readily visible. The green pods turn yellow in the fall and then yellow-brown, and can persist through the whole winter. In China a yellow dye is extracted from the pods for use in the silk industry.

There are a number of diseases and insects that prey on the Scholar-tree, but none too devastating. Cankers can cause branch dieback, but leafhoppers are perhaps the worst problem, feeding on the new tips and causing witches brooms to develop (a proliferation of adventitious growth). This is a particular problem on young trees and is difficult to control. As a young tree, it is a little cold sensitive, and can suffer some dieback on the main stem, but once it reaches about 1½" caliper develops good winter hardiness. The falling flowers create a thick creamy white carpet in late August, so don't park your car under the tree in August. There are a few improved cultivars available, most notably Regent®, selected by Princeton Nurseries for faster growth and younger flowering.

It is only recently that this species was separated from others in the Sophora genus, and named Styphnolobium, apparently because it lacks the ability to fix nitrogen through the symbiosis with Rhizobia bacteria like members of the Sophora genus. This seems a pity, because Sophora is a much easier name than Styphnolobium! Under any name this is a first-class flowering tree and worthy of much greater use. There are a few planted around the crossroads of Marsh Rd. and Pittsford-Palmyra Rd., near the Pittsford post office.

Other Species

Two other non-native species of Fabaceae, which may be encountered in our area, are Goldenchain Tree (Laburnum spp.) and Mimosa (Albizia julibrissin). Both of these are beautiful in flower, but are marginally hardy and/or susceptible to numerous problems. The Goldenchain Tree usually encountered (Laburnum ×watereri) is a hybrid of two European species (L. alpinum and L. anagyroides). It sports alternate, trifoliate bright green leaves, with no appreciable fall color, and bright yellow fragrant flowers in 6 to 10" long pendulous racemes in late May, making a spectacular show. Hardy to Zone 5, the trees tend to suffer greatly from twig blights and cankers, causing significant dieback and loss of major branches. I know of no good-looking specimens in our area, although spectacular examples can be seen in Britain.

Mimosa, or Silk Tree (Albizia julibrissin) is native from Iran to China. It is a broad spreading tree to about 25' with alternate bipinnately compound leaves. In late May to early June, fragrant pink powder puff-like flowers are produced in small clusters. More flowers are sometimes produced sporadically through the summer. Straw-colored pods, 5 to 7" long, mature in October and often persist through the winter. Considered something of an invasive pest in the South, where it is extremely well adapted and a prolific seeder, Mimosa is adaptable to a variety of soils, especially high pH, drought and wind resistant, but needs lots of heat to flower well. It is also susceptible to Fusarium wilt, especially in the South, leaf spot and rust, as well as webworms. Hardy to Zone 6, there are a few examples in our area in protected locations and near the lake. A variety introduced from Korea, 'E.H. Wilson', offers increased hardiness, perhaps to Zone 5, although my experience with this variety suggests that small trees and seedlings may not acquire full hardiness until they reach larger size, perhaps 1" caliper. The jury is still out on this.

With the exception of the popular redbud, most of the other species of Fabaceae are relatively unknown and still quite rare in cultivation, but they have much to offer in the world of ornamental horticulture. In the interests of diversity, it's time to look at some of these species and give beans a chance.