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Fasciation or cristation is an abnormal
development of an
apical meristem characterized by
indeterminate
proliferative growth. A plant becomes crested when its
apex
develops laterally from a
linear meristem rather than a single point |
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From the Latin word
“fascia”, meaning “a band”.
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(Photo 1)
Rebutia heliosa
forma
cristata
This crest clearly shows the
elongated line of growth (due to a linear meristem) at the
tip. |
Fasciation
or cristation is a widespread
phenomena that may
randomly affect
vascular plants both in
nature and in
culture. Out of 290
families the fasciations were found at least in 107 of them.
There are no direct confirmation of absence of fasciations in
any of
taxonomic groups of
vascular plants.
A fasciation (abrupt changes of
organ forming activity of
meristems resulting from
somatic mutations) is an abnormal enlargement or
coalescence of a shoot
tips ( not a
disease) in which a single
apical meristem has become unusually broadened and flattened
, suggesting many
stems have fused together (Photo 1), this establish the
following
unlimited growth,
As a result the shoots have
axial symmetry instead of
central symmetry. The
plants reached take initially the form of a fan, then undulate,
and end up resembling brains (Photo 2).
Side shoots are usually absent or remain small and
undeveloped. It is especially prevalent in species with
indeterminate growth patterns. Although there is another
much rarer type, characterised by a ring-shaped growing point,
which produces a hollow shoot (ring
fasciation). |
Some
cristation are real living sculptures, sought after by
collectors, coveted by plant amateurs, and widely cultivated by
commercial grower, they look very outstanding when potted and
certainly attract a lot of attention.
The plant showing this abnormal growth are indicated as "forma
cristata" or "f.
cristata" following the name of the species |
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1) |
Genetic Fasciation
It is not truly known if the fasciations are
inherited. However, the tendency toward fasciation is
transmissible by
budding and
grafting once the plant develops a fasciation. Growers who
prune off fasciated
branches often find this condition returns with the
development of new branches. At least in some occurrences
fasciation is controlled in plants by
genes. Many species exhibit true-breeding
fasciated
lines, although the
expression of the
character is very dependent on
environmental conditions - especially
temperature and
nutrition. Because the
gene
conditioning fasciation exhibits incomplete
penetrance, the character may assume any of many degrees of
expression. The cockscomb celosia (Celosia argentea var.
cristata) is an excellent example of a plant with inherited
fasciation. |
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2) |
Physiological Fasciation |
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A) |
Natural
Environmental
Factors |
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I |
Attack by
Insects. Several insect species have been found to produce
fasciation. |
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II |
Pressure.
Underground
shoots that pierce the
ground, such as asparagus, tend to become fasciated. |
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III |
Seasonal Influences. Time of
sowing may
influence the degree of fasciation, with earlier sowing
appearing to produce larger numbers of fasciated plants.
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IV |
Crowding: has often been reported to produce a decrease in
the percentage of fasciated plants. |
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V |
Temperature. Low temperature followed by high temperature
causes fasciation in Hyacinthus and may be a cause of fasciation in
other plants. |
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VI |
Mineral Deficiency.
Zinc
deficiency is known to cause fasciation. |
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B) |
Artificially Applied
Factors |
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I |
Decapitation of
Seedlings and
Defoliation: Amputation of the main
stem
of seedlings induces fasciation in several
species. |
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II |
Wounding of the
Growing Point: Wounding causes fasciation as well as all
kinds of abnormalities. |
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III |
Ionizing Radiation: (X-rays and gamma-rays). |
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IV |
Infection with
Fungi,
Bacteria, and
Viruses |
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V |
Polyploidizing Agents (colchicine, morphine,
phenyl-urethane, etc). |
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VI |
Nutrition Good nutrition, including high rates of
nitrogen, increases the occurrence of fasciation. |
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VII |
Water Shortage Plants with
indeterminate inflorescences when kept under
drought conditions prior to
flowering and then subjected to heavy
watering and high
nutrient levels will produce fasciations |
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VIII |
Application of
Growth Regulators and
Herbicides: TIBA (2,3,5-triodobenzoic acid), for example,
induces fasciation, particularly
ring fasciation, and many other abnormalities, including
distortions and fusion of organs. |
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IX |
Photoperiod: Fasciation may be induced by increasing or
decreasing the photoperiod - the lenght of day experienced by the
plants.
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Cristation in
cactus and
succulents: |
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(Photo 3)
Turbinicarpus pseudopectinatus forma inermis cristata |
Cristation is a quite
frequent phenomenon in
Cactaceae ( reported in more than 50
genera) and also in many other succulents
family like in
Euphorbiaceae,
Crassulaceae,
Asclepiadaceae, etc.. A pure cristation is also completely
different then
monstruosity, where
axils (areoles)
are multiple-activated
and the
apical meristem stopped
growing.
All
column-like and
globular cacti, as well as
Opuntias, can be
touched by this
anomaly growth form which remains however rare because it
cannot be caused. One did not find yet a cristation for all the
existing species.
Cactus horticulturists and
collectors believe that cristation results from
somatic mutation(s) at the
apical meristem region of the main
stem or
branches and that a predilection for occurrence of this
mutation is
heritable. |
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As a result of
unlimited growth of
linear meristem (see: photo 1) the stem gets flattened,
areolae with
spines are situated on all the
surface of the crests. The number of
ribs and/or of
parastichs (spiral lines formed by areoles) increases but
the structure of areolae themselves does not practically change.
Depending on the age there are
fan-shaped (Photo 6),
wavy and
brain-shaped crests. More thick crests seldom grow into
brain-shaped (e.g. crests of Carnegia gigantea). All
fasciated species grow faster than normal ones which corresponds
to the opinion of most authors, the increase of
photosynthesizing surface leads to better
carbon
nutrition and faster
growth of fasciated plants. Crests may remain at any
stage for a long time. But at the stage of brain-shaped
crest when the curves begin to crowd
defasciation (Photo 4) occurs rather often. That is the
linear meristem turns into a number of small
apical meristems that form normal
shoots. Seldom defasciation occurs without any reason at an
earlier stage of the development of the crest. In general with
age meristem gets less
active or not active at all. The growth continues only at
some parts of linear meristem. Thanks to this process the upper
surface becomes uneven. The more active parts are usually
situated at its ends. This type of developing crest prevails
among cacti, and for a long time it was considered to be the
only possible. |
(Photo
4)
Mammillaria
luethyi
forma cristata
an example of crest
defasciation |
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(Photo 5)
Strombocactus disciformis
forma cristata
Juvenile and mature structure in response to the use of
different grafting stocks. |
Many authors affirm that the crest
of
cacti has another specific feature. In spite of their rather
large size the
areolae frequently kept their
juvenile
structure and are situated like at the
seedlings of the
species.
Consequently the physiological age of crest may not depend on
its real age and be determined by the
stage of the development at which it appeared. It is quite
possible that the crest that appeared at a juvenile plant will
not be able to
bloom during its life-time.
But this thesis is not based on a correct observations, the
apparent age of the crest depends mainly by the
hormonal balance furnished by the
grafting stock. It is a well known
phenomenon that crest grafted on different stocks may be
very different one from each other.
The fact that crest forms flowers rarely is in part due to the
consuetude to graft the crest on strong stock that enhance only
a fast growth and delete the natural
maturation and flowering. (photo 5) |
In the
ontogenesis a crest can appear any time, but development of
crests at large
columnar cactus species ( such as in saguaro Carnegia
gigantea) in the early
stages of ontogenesis is unlikely. On the other hand small
species may crest early already at the
cotyledons
stage.
That means fasciations can take place even in the first days of
a
seedling or at the stage of the forming of the
embryo in the
seed. As practice shows when cactus fanciers grow cacti out
of seeds fasciations often take place at germs and
juvenile plants especially when the regime changes (temperature,
humidity,
grafting onto a strong
stock). It also takes place in any growing phases without
any apparent reasons. |
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Fasciation in a
taxon is clearly correlates with the degree of
succulent characteristics of
stems. Among widely spread fasciated plants there are many
members the most advanced
subfamily Cactoideae, which grows in
arid conditions and are remarkable for the high degree of
succulence. While
primitive
subfamily Pereskioideae which grow in the conditions
of sufficient or excessive
humidity, have a high percentage of
photosynthesizing surface to the volume of the plant and
have almost no fasciations. A larger number of fasciations is
found among
xerophytes as compared with
hydrophytes were mentioned earlier for other
families as well. Among
succulents the frequency of fasciations is most likely to be
at
evolutionally
advanced
taxa with highly
specialized
vegetative organs. It is obvious that
environmental conditions are more important for the
appearance of fasciations than the origin of the species with
high frequency of fasciations. |
(Photo 6)
Geohintonia mexicana
forma cristata |
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(Photo 7)
Echeveria coccinea
San Bartolo Co. Hidalgo,
Mexico forma cristata |
Cultivation of crested cacti and
succulents.
Cultivation of the cristate forms of cacti is worthy of a
special mention because an accidental appearance of a crest
happens quite often and these plants attract attention of
collectors thanks to their prominent ornamental features.
Furthermore the crested forms can be usually
reproduced vegetatively without difficulties Many crests
should be kept on the dry side, in other words, grown hard. Too
much
water and/or
fertilizer can cause cracks and spreading. Trimming any
normal shoots off helps the crested form grow better and truer
to form, but sometimes these normal shoots can crest again after
some normal growth. Cuttings from crested cactus should be
grafted for best results.
Cuttings from other crested
succulents can be replanted after the normal waiting period.
Keep these very dry for at least a week or preferably two weeks
and on the dry side during their normal growing cycle. For
euphorbias,
this would be in the
Autumn. |
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For some
leaf succulents it is sufficient to have any part of the
mother plant - a
leaf or even an ordinary, non-crested shoot (Photo 7) in
order to reproduce crested form. In other cases only a fragment
of the crested shoot is suitable for reproduction whereas leaves
and normal, not crested shoots don't
inherit desirable qualities. |
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