By Katie Stannard
Winter visits to the conservatory at Matthaei Botanical Gardens are a treat for the senses: warm temperatures, lush greenery, and plants in bloom or in fruit. A visitor favorite is one of the banana tree plants, which just finished a fruiting cycle.
The banana is the variety Gros Michel or “Big Mike,” Musa acuminata ‘Gros Michel,’ a remnant of this ill-fated clone of seedless banana. Gros Michel, or fat Michel, so named for its thick fruits, was devastated in the 1950s and 1960s by a fusarium wilt (F. oxysporum f. Sp. Cubense, or Foc), also commonly known as Panama disease or banana wilt. As this disease spread it wiped out many commercially-grown banana fields of the day.
Despite its height which makes it look like a tree, it’s not a true tree after all.
An excursion into botany by way of a conversation with Mike Palmer, Matthaei-Nichols research coordinator, will guide our curiosity.
A broad definition for a tree is a fifteen foot or taller plant that has woody stems. Though Gros Michel does grow more than 15 feet tall, it has a different vascular arrangement as a herbaceous plant.
In woody plants, the presence of lignin within the cell walls makes them sturdy and slow to break down or decompose–hence those plants last longer. The cell walls of herbaceous plants are made up of cellulose, which though strong decomposes more readily than lignin.
The arched, hanging banana plant stalk with fruits from October, 2021.
Photo: Katie Stannard.
Like hosta, eyes emerge from the large underground clump, producing stems which contain vascular bundles. Long trunks or pseudostems are actually leaf material which has continued to grow, forming stem stalks. A cross section of a cut fruiting stalk (see photo) shows what looks like plant or leaf material compacted to form the stem.
Once the banana finishes fruiting, the stalk would eventually topple over–but like this one removed in early January, generally they’re cut down for safety reasons.
The last time Gros Michel flowered and fruited was about 18 months ago, in June, 2020.
Diameter cut of the stalk is about 6 inches across. Photo: Katie Stannard.
The removed banana plant stalk. Photo: Katie Stannard.
Once the fruiting stalk was removed, only the stump remained. Photo: Katie Stannard.
Most of the other stalks that emerge will not fruit. But in growing and conducting photosynthesis, they add to the energy of the crown. On non-fruiting stalks, leaves will mature, senesce (gradually deteriorate) and then fall.
A zone of female flowers (which become fruits) occurs at the tip of the stalk. As the flower stalk elongates, every layer of brownish petals includes a zone of male flowers, which keep emerging until the stalk falls. Ironically, these separate zones prevent self-fertilization and encourage cross-pollination. Yet Gros Michel is parthenocarpic: it produces fruit without fertilization. Fruits are sterile and seedless, the desirable quality for which they’ve been bred.
Photos of male flowers on Gros Michel banana. Photo: Mike Palmer.
Banana plants grow as rhizomes, modified horizontal underground reproductive stems which develop roots and shoots from nodes, and store nutrients needed for plant growth. It’s similar to how hosta clumps develop and can then be divided into segments for propagation. Chopping off a segment means it’s the same plant.
Often visitors might ask whether the bananas were hand-pollinated by staff. No, said Palmer, they reproduce through asexual reproduction. Essentially if one cuts a part of the rhizome clump, that’s an exact clone which will grow.
The trouble with cloning, noted Palmer, is that the same genetic material produces a monoculture, which over time can become more susceptible to disease or insect infestation–like what happened with Panama disease. Though initially bred to be resistant to banana wilt, there’s concern that today’s commonly available banana variety, Cavendish, will also eventually succumb. A strain known as Foc TR4 is impacting Cavendish fields in some parts of the world. However, tropical plant research institutions are working to develop new varieties that will be disease resistant, taste good, and be easy to propagate.
A Gros Michel banana. Photo: Katie Stannard.
What are some differences between Cavendish and Gros Michel? Gros Michel produces prolific shorter, wider fruit in bunches with thick skins and intense flavor.
According to Matthaei-Nichols curator David Michener, Gros Michel was part of a set of plants procured over time from the Missouri Botanical Garden just before and after World War I. Likely in our collection since 1921 or 1922, it’s been growing and fruiting for about 100 years!
So how has this Big Mike specimen survived without succumbing to Panama disease? “Because the conservatory is an island in its own stasis, we’re very careful to not introduce any other plant or insect material into it,” remarked Palmer.
Mike Palmer prunes banana fruit from the stalk. Photo: Katie Stannard.