Mostly Mulberry: A Natural History

Guest Contributor: Georgia Silvera Seamans, founder of Local Nature Lab, a nature education nonprofit based in New York City. She holds a PhD from University of California Berkeley and is an adjunct professor of environmental studies. She has published peer-reviewed articles in Urban Forestry & Urban Greening  and Arboriculture & Urban Forestry. She also has bylines at Audubon.com, PopSci.com, BBG.org and in City Trees. Georgia is a founding member of #BlackBotanistsWeek and serves on the board of NYC Bird Alliance.

I grew up on the island of Jamaica eating roasted breadfruit (Artocarpus altilis). Sadly, I eat much less breadfruit now living in New York City.

One of the ways I remain botanically connected to the island is through my encounters with mulberry (Morus spp.) and Osage orange (Maclura pomifera). These two species are in the Moraceae family, along with breadfruit. In this piece I mostly focus on the mulberry with forays into breadfruit, Osage orange and other Moraceae fruit.

What makes a Moraceae species?

The primary characteristic that defines plants in this family is a syncarp or synconium fruit. A syncarp develops when tightly arranged flowers are fertilized and mature into an aggregate fruit.

The fruits within the syncarp are also considered drupes. A drupe is a thin-skinned fleshy fruit with a central seed. White latex is another feature of this family.

In addition to Morus, five other genera populate the Moraceae family: Brosimum, Treculia, Ficus, Maclura, and Artocarpus. Figs (Ficus) are delicious to eat. I do not prefer jackfruit (a childhood food) or durian (another Artocarpus). Family members and very good friends love to feast on the latter fruits.

I first encountered the Osage orange in Arlington, Virginia. The large chartreuse-colored, brain-textured fruits are striking. The species is anachronistic, meaning the fruit persists in the absence of its co-evolved herbivore. In “Anachronistic Fruits and the Ghosts Who Haunt Them,” Connie Barlow profiles two scientists in pursuit of identifying the extinct animals who would have eaten the Osage orange. The strongest case is for Pleistocene-age horses.

In Re-peopling Prairie: History, Ecology, & How They Can Better Inform Prairie Science, Liz Anna Kozik writes that Osage orange “travelled Turtle Island long before Europeans did.” However, the association between plant and prairie settlement began with “one gifted tree in Saint Louis.” From there, the plant was propagated in Eastern U.S. states and entered the global horticultural trade. Osage orange would make its way back to the prairie as “thorny” fencing in a landscape largely devoid of woody plants.

Breadfruit also has a settler-colonial history. Enslavers imported breadfruit from Tahiti to Jamaica and other English colonies in the Caribbean. In Jamaica, enslaved people were already eating a diet composed of indigenous and African-origin starches such as “cassava, yam, taro, plantains and bananas.” Enslaved people initially refused to eat breadfruit, instead feeding it to pigs. Breadfruit only became an embedded in Jamaican foodways decades after emancipation. 

Some mulberry natural history

In the Eastern U.S, you might encounter both red mulberry (Morus rubra) and white mulberry (M. alba). Red mulberry is native to Eastern North America. The species is a wind-pollinated, understory tree. White mulberry, native to China, has naturalized in the U.S. It is fast growing and tolerant of a variety of soil and environmental conditions, and was introduced to Virginia in the early 1600s to launch the silk industry in the U.S. The venture was unsuccessful. Silk production is labor intensive!

To understand the silk story, let’s consider that people first bred the domestic silk moth (Bombyx mandarina) from the wild silk moth (B. mori). The former is supersized in comparison to the wild silk moth. Agricultural silk moths cannot fly very well! Sadly, the wild silk moth might be extinct in the wild.

A silk moth caterpillar takes 2-3 days to spin a cocoon made of a single, continuous strand of silk that is “up to 10 city blocks long,” the equivalent of about half a mile. In order to maintain the integrity of the silk strand, the pupa with the cocoon is killed.

You might take comfort in knowing that silk is more than fashion. The material has medicinal applications. Silk fibers are used to create wound dressings and to engineer tissue and blood vessels.

The numerical facts of sericulture are astounding. The latest issue of Orion magazine features an essay about silkworms, “Heavenly Worms,” by Zhengyang Wang. The Tianhong Silk Co. Ltd. in China’s Sichuan Province “works with four thousand local households across eight thousand acres of mulberry fields to produce more than 150 tone of silk annually from 600 million moth cocoons — enough to extend to the sun.”

The numerical facts of sericulture are astounding. The latest issue of Orion magazine features an essay about silkworms, “Heavenly Worms,” by Zhengyang Wang. The Tianhong Silk Co. Ltd. in China’s Sichuan Province “works with four thousand local households across eight thousand acres of mulberry fields to produce more than 150 tone of silk annually from 600 million moth cocoons — enough to extend to the sun.”

China historically imposed the death penalty on smuggling of silk out of the country. However, in 552 AD, two monks successfully stole silkworm eggs or larvae and delivered them to the Eastern Roman or Byzantine Empire. This ended the Chinese monopoly on silk production. 

Black mulberry is native to Iran. It is grown in the U.S. in “warmer, drier areas” according to multiple sources on the internet.

Mulberry is not a berry

Even though the fruit has “berry” in the name, mulberries are not true berries. A true berry is a fruit that comes from a single flower’s single ovary. An example is a blueberry. By contrast, the mulberry is a multiple fruit composed of many fruits from many flowers (other examples are blackberry and pineapple). The strawberry is different; it produces an aggregate fruit which occurs when a single flower has multiple ovaries.

How to tell your mulberry fruits apart? The fruit of the red mulberry is longer than that of the white mulberry. The color of the mature fruit is not a diagnostic of either species.

Have you come across a mulberry that looks like a cross between a red mulberry and a white mulberry? You’ve most likely met a hybrid of the two species. The two species hybridize easily which is a conservation concern, at least in Pennsylvania.

Leafy matters

The leaves differ in terms of both texture and shape. White mulberry leaves are glossy and smooth, while the leaves of red mulberry are rough textured on top and softly hairy on the underside. A mulberry’s leaf can take various shapes, including twice-lobed and thrice-lobed. Leaves on the older shoots of white mulberry tend to be unlobed.

There is always a bird connection

This article is based on a talk I gave at the end of June. Luckily I mentioned my preparations to some folks in the bird world (NYC Bird Alliance). Science Director Dustin Partridge told me of great egrets nesting in mulberry trees!

In NYC, great egrets thrive on Hoffman Island, an 11-acre artificial island off the coast of Staten Island. Other wading birds also nest in trees, including great blue heron, snowy egret, green heron, black-crowned night heron and yellow-crowned night heron.

Next time you meet a mulberry, consider the fascinating stories behind the plants — especially the most mundane species.