Ask A Scientist© Biology Archive

name         Adele
status       other
age          20s

Question -   Why do Banana trees grow bananas??  I've been asked this
question and no-one I know can provide an answer!
Bananas do not have seeds in them to reproduce the tree (e.g you can grow
a lemon tree from the seeds in the fruit but not a banana tree from a
banana) What evolutionary justification is there for a banana tree to bear
fruit?
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Hi Adele! you are right, one cannot seed a banana tree,
still that kind of vegetal is reproduced and grows...
As many other plants they have an asexual reproduction,
where the new plants are identical in every respect to
the parent plant.The asexual reproduction involves no
union of cells or nuclei of cells, there are not mingling
of genetic traits.
Banana plant is a gigantic herb that grows from an under-
ground stem ( rhizome),and forms a false trunk with leaves.
There emerges a large flower spike, with numerous
individual flowers, that bends downward to become fruits.
After the plants had fruits, they die and are replaced
by others that arise from the underground stem, and
that process can keep on going for many years.
Right?
Thanks for asking NEWTON!

Mabel
(Dr. Mabel Rodrigues)
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Dear Adele,

Cultivated bananas are parthenocarpic (with sterile fruit), while wild
bananas did have seeds.  The fruit was probably a result of co-evolution
with its pollinators and the animals that feed upon it and spread its seeds
before cultivated forms.

http://www.crfg.org/pubs/ff/banana.html
"Fruits: The ovaries contained in the first (female) flowers grow rapidly,
developing parthenocarpically (without pollination) into clusters of
fruits, called hands. The number of hands varies with the species and
variety. The fruit (technically a berry) turns from deep green to yellow or
red, and may range from 2-1/2 to 12 inches in length and 3/4 to 2 inches in
width. The flesh, ivory-white to yellow or salmon-yellow, may be firm,
astringent, even gummy with latex when unripe, turning tender and slippery,
or soft and mellow or rather dry and mealy or starchy when ripe. The flavor
may be mild and sweet or subacid with a distinct apple tone. The common
cultivated types are generally seedless with just vestiges of ovules
visible as brown specks. Occasionally, cross-pollination with wild types
will result in a number of seeds in a normally seedless variety. "

http://www.orst.edu/food-resource/a/weaver/r6.html
"The anatomy and development of the banana are discussed by von Loesecke
(1949), Simmonds (1959), and Palmer (1971). The edible banana is
parthenocarpic and is propagated from a rhizome. The fruit consists of an
inedible skin which encircles the edible pulp. "

http://vertigo.derby.ac.uk/BiologicalImaging/Shows/fys95/DW2.html
"The banana (Musa accuminata) is a berry formed from a superior ovary of
three joined carpels arranged in an axile placentation. The flowers are born
on long and pendulous inflorescence which are usually unisexual, that is,
the female flowers are born near to the base of the peduncle (producing the
typical banana berry fruits) whilst the male flowers are born on the tip of
the same peduncle. Seed may be produced or more usually, develop the berry
parthenocarpically. Both the seeded and the parthenocarpic berry are very
similar in structure when flowering."

Sincerely,

Anthony R. Brach, Ph.D.
=========================================================

Adele,

My understanding is that in the 'wild', banana trees do indeed bear viable
seed within the fruit.  I believe the commercial banana has been bred to
have only the vestige of seeds, which then promotes easy consumption.
Recent research and development has produced watermelons also with reduced
or eliminated viable seed.

Thanks for using NEWTON!

Dr. Rupnik
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