Floral Phyllotaxis
Phyllotaxis is Greek for “leaf
arrangement” but it is also a
useful concept for describing
the arrangement of flower parts.
The basic floral phyllotaxic
arrangements include:
Spiral
Simple-whorled
Complex-whorled
Irregular
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Floral Phyllotaxis
Spiral Phyllotaxis
In spiral phyllotaxy, the
individual floral organs are
created in a regular time
interval (plastochron) with the
same divergent angle.
A plastochron is the term used
to describe the time between
successive organ initiation.
The divergent angle in a flower
with spiral phyllotaxy
approximates 137.5 degrees,
which is indicative of a pattern
that follows a Fibonacci series.
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Floral Phyllotaxis
Spiral Phyllotaxis
Fibonacci series typically describe spirals found in nature. It is calculated as a
series where the previous pair of numbers sum to the next number in the series.
The series is 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89
Spirals of disc florets in sunflower
(Helianthus)
Ammonite fossil
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Floral Phyllotaxis
Spiral Phyllotaxis
As illustrated in a coneflower inflorescence, there is actually one set of spirals
(parastiches) in a clockwise direction and one set in a counter-clockwise direction.
Spirals of disc florets in purple
coneflower (Echinacea).
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Floral Phyllotaxis
Spiral Phyllotaxis
Floral organ spirals follow a numerator and denominator set of offset Fibonacci
numbers (1/2, 1/3, 2/5, 3/8, 5/13, 8/21, 13/34 …). The numerator is the number
of times or turns around the axis to get back to the initiation origin. The
denominator indicates the number of organs initiated during the turns. Therefore,
a 2/5 would indicate 2 turns around the axis and 5 organs to return to the origin.
3/8
2/5
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2/5 spiral
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A 3/8
spiral
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Floral Phyllotaxis
Spiral Phyllotaxis
A side view of a Camellia flower
shows the spiral pattern in the petals.
This double flowering Camellia shows
spiraling around a central axis described
by a Fibonacci series.
A 2/8 spiral
4
6
1
7
3
2
0
5
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Floral Phyllotaxis
Spiral Phyllotaxis
Spiral phyllotaxy is common in the basal
angiosperms and in the fossil record
suggesting that it is an ancestral form.
However, this is not entirely clear
because examples of whorled phyllotaxy
are also present in advanced angiosperms.
Nymphaea
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(Nymphaeaceae)
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Drimys winterii (Winteraceae) shows
a spiraling pattern in the stamens.
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Floral Phyllotaxis
Spiral Phyllotaxis
Magnolia flowers nicely show the spiraling
Pistils
pattern in the stamens and pistils.
(developing
ovules)
Pistils
Stamen
scars
Stamens
Magnolia flower after petal drop.
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Floral Phyllotaxis
Whorled Phyllotaxis
In whorled phyllotaxy, the
individual floral organs are
created in a very short time
interval (plastochron) and
therefore appear to be on the
same radial plane rather than
in a spiral.
Whorled phyllotaxy tends to
be an advanced floral pattern
and most of the monocots
display whorled phyllotaxy.
Trillium
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Floral Phyllotaxis
Simple-Whorled Phyllotaxis
In a simple-whorled phyllotaxy, there
is an equal number of floral organs in
each whorl. It is common for organs
to alternate from whorl to whorl.
Sepals
Petals
Stamens
Petals
Stamens
Carpels
This floral diagram illustrates a flower with
4 sepals, 4 petals, 4 stamens and 4 carpels
that alternate their position in the flower.
Ixora
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Floral Phyllotaxis
Simple-Whorled Phyllotaxis
Simple-whored phyllotaxy are most usually in sets of threes, fours or fives.
Crocus
Ixora
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Euonymus
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Floral Phyllotaxis
Complex-Whorled Phyllotaxis
In a complex-whorled phyllotaxy, the
number of organs differ between whorls.
Sepals
Petals
Stamens
Carpels
This floral diagram illustrates a
flower with 4 sepals, 4 petals,
8 stamens and 4 carpels.
Kalanchoe
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Floral Phyllotaxis
Complex-Whorled Phyllotaxis
With complex-whorled phyllotaxy there is a duplication of organs in a whorl.
Iberis
Zepharanthes
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Dionaea
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Floral Phyllotaxis
Complex-Whorled Phyllotaxis
In complex whorls, the duplication most often occurs in the petals or stamens.
In this jasmine flower, there is
an extra set of 5 petals.
10 petals
20 stamens
10 petals
Sempervivens
Jasminum nitidum
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In this stonecrop flower, there is an extra
set of petals and two sets of stamens.
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Floral Phyllotaxis
Irregular Phyllotaxis
In irregular phyllotaxy, there is no easily recognized spiral or whorled
pattern. It is more common in flowers with numerous petals or stamens
and may be accompanied by staminode production.
Fertile
stamens
Staminodes
Couroupita
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Barringtonia
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