Fantastic Flora

  • SALLY L. WHITE –

When Beans Grow on Trees

Eastern Redbud(Cercis canadensis), and the Locusts (Black Locust, Robinia pseudoacacia;
Honey Locust, Gleditsia triacanthos)—Pea Family (Fabaceae)

Spring splendor: The brilliant, and abundant, flowers of eastern redbud in early May, before leaves appear, make it a highlight in the landscape. Redbud is virtually cloaked in flowers, thanks to its ability to produce flowers on older branches, and even the trunk (cauliflory).

Can you imagine a prettier sight in early spring than an Eastern Redbud tree in full bloom? Seeing its magnificent magenta flowers, I was delighted to find it here in my new backyard. Our tree met her demise in a major snowstorm of March 2018, but thanks to prolific seed production over the years, we welcomed several shrubby offspring, some already half grown. 

In the tropical forests where they evolved, woody legumes are exceedingly abundant. In temperate zones, we have only a few. Of more than 150 legumes, only eight woody species are listed in New York’s Flora Atlas. There’s some debate as to whether they’re native, but they are probably here to stay. Our conditions may, if climate change proceeds unchecked, grow more hospitable to them. 

Eastern redbud is the only tree in our area that exhibits cauliflory (literally, stem-flowering). The classic butterfly-shaped, or papilionaceous, flower is characteristic of legumes in temperate regions, but in the tropics, this large, diverse family displays more variety in flower types.

Eastern redbud is not just a pretty springtime face— it’s also an intriguing tree. As a smallish understory tree, eastern redbud occurs in open woods, edges, and hedgerows. Some of its qualities are unusual in our landscape and even in its own family. Unlike many other legumes, eastern redbud has “entire” leaves, each one a single, lovely, heart-shaped piece. Until you see that “butterfly” flower, you might not think it’s in the pea family at all. More surprising, the flowers arise directly from the stem or trunk of the tree, a feature called cauliflory that is also found in tropical trees and shrubs such as cacao (which gives us chocolate), coffee, figs, and papaya. 

Distinctive pod fruits, each holding up to ten seeds, reveal redbud’s affinity to the pea or bean family. (Pods or beans are called “legumes” and, in fact, define the family.) Pods of redbud are two to four inches long, dainty compared to the robust pods of honey locust, and ripen to brown. Seeds are eaten by songbirds. The pods arise directly from the main stems rather than the new growth, as the flowers did. Early June. The “entire” leaves of redbud are bright green and heart-shaped and appear after the flowers. Leaves are eaten by several kinds of caterpillars and, as here, carved by leafcutter bees (likely genus Megachile).
The “entire” leaves of redbud are bright green and heart-shaped and appear after the flowers. Leaves are eaten by several kinds of caterpillars and, as here, carved by leafcutter bees (likely genus Megachile).

Cauliflory is one way plants may improve their chances of finding pollinators. Flowers are offered not at the tips of branches, but often on the branches and even lower on the trunk. This habit makes them accessible to low-flying insect pollinators, putting the nectar and pollen buffet in reach of guests thatare unlikely to access high tropical canopies. Redbud attracts low fliers like carpenter bees and honeybees. 

The fragrant flowers and sweet pods of honey locust come at a price. In the wild, impressive thorns protect the branches, and even the trunks, of honey locusts.

Beauty and the Beasts

More robust than the dainty redbuds, black locust and honey locust are overstory trees that may reach, in the latter, 100 feet in height. Black locust is smaller and sometimes considered invasive. In New York State, it is “regulated” due to its root sprouting habit, but not prohibited. (It’s okay to plant, but only in your yard.) Like redbud, locusts are not universally considered native here in New York, but are native to states south and west of us. As pioneer species, they can escape and establish populations in areas where they may seem to be naturally occurring. 

Images by QKA Light Photography

Both locusts have durable wood used for fenceposts, tool handles, and even mine timbers. Although eaten by wildlife and livestock, honey locust pods can become a nuisance in captivity, littering lawns and sidewalks when they ripen and fall. The trees are armed by formidable thorns. Now that they’ve been tamed by plant breeders, honey locusts make wonderful street trees or decorative accents in home landscapes. Your local nursery can likely provide thornless varieties as well as trees that don’t produce those messy pods, making these variants popular in more urban settings.

Eastern redbud is earliest to flower of the three species, and perhaps most spectacular, bringing its bright pink touch of spring to our landscapes when other trees are still somber. Keep an eye out for it as you travel the roadsides this spring—I can’t wait to spot more locations for this charming tree.

Posted on April 23, 2022 by . This entry was posted in Botany, Environmental, Finger Lakes, Gardening, Nature and tagged , , . Bookmark the permalink.