A close-up view of Forest Frost Hens and Chicks
Close-up View of
Forest Frost Hens and Chicks
by Brian Johnston (Canada)
are extremely hardy, mat-forming succulents of the family
known as ‘Hen
and Chicks’ or ‘Houseleeks’. Native to the mountains of
the Middle East, and Central Asia, they grow close to the
fleshy leaves grouped around one another in a very tightly
rosette. The ‘hen’ is the main plant, and the ‘chicks’ are
offspring, which start as tiny buds on the main plant, and soon
their own roots, taking up residence close to the ‘hen’.
Hens and chicks have a very
history of cultivation. It is said that the Frankish King
Charlemagne (742-814 AD) suggested to his subjects that they
plant on their thatched roofs in order to guard against fires
thunderbolts, storms and sorcery. Since succulents do
water in their leaves, they may help in the first two cases, but
sorcery – perhaps not!
The genus name Sempervivum is Latin for
alive’ (evergreen). Arachnoideum,
the species name, relates to ‘spiders’. In this species
of the leaflets are connected by thin hairs that closely
arachnoideum has many cultivars, of which ‘Forest
one. Some arachnoideum
have very dense cobwebbing, while others have little.
Frost’ seems to be positioned somewhere in the middle of the
terms of this characteristic.
When I first found this
cultivar at my local greenhouse, I had no expectation that it
bloom during the spring or summer period. I was
However, later in the summer, the same greenhouse had a couple
blooming examples, which I obtained in order to show its entire
life-cycle. This article has been produced by using images
of the three ‘Forest Frost’ plants.
It should be kept in mind that
Sempervivums are monocarpic, meaning that a
particular hen flowers only once, and then it dies.
by the time that this happens (usually several years), it has
produced many chicks to take its place.
The first image in the
the series shown below, show several ‘hens’ (4 - 6 cm diameter),
their smaller chicks (1 – 2 cm diameter).
Two higher magnification
show the dense tufts of cobwebbing at the leaflets’ tips, and
strands that connect each tip to its nearest neighbours.
Although Sempervivums can reproduce
when the plant finally flowers, a much more common reproductive
technique is vegetative
This occurs when the hen ‘offsets’. Here, the base of the
produces what look like thin, root-like stems called stolons with tiny chicks at
ends. Each offset develops roots of its own and becomes
independent of the parent when the stolon withers and
dies. Some Sempervivums
produce offsets on
the ends of long stolons, which produces a less tightly packed
group. Vegetative reproduction produces offspring with the
characteristics as the parent plant. The four images below
the tight packing of a family group. Notice the light
stolon visible in the middle left of the first image.
Another view can be seen in
images that follow.
The leaflets at the centre of
chick rosette are green in colour, while those further out have
Cobweb density is very
different hens and chicks.
When viewed at a very close
it is evident that the threads comprising the cobweb originate
tip of a leaflet. While the chick is still very tiny, the
become tangled and caught by nearby leaflets, and as the
grows, a cobweb is produced.
For some unknown reason, the
occasional chick has many fewer threads. Notice that the
threads allows us to see the outer surfaces of the leaflets much
clearly. Hair-like projections cover all surfaces.
Many of the chicks are not
rooted to the soil in the container, and they jiggle when
touched. This one was precariously balanced between a
When removed from the
is evident that there is no cobwebbing underneath.
A longitudinal cross-section
chick reveals that the leaflets grow from a colourless,
The four images that follow
what appears to be the formation of a new chick, but the shape
right. Instead of a ball, a stalk appears to be growing
the base of the rosette.
A couple of weeks of patient
observation resulted in the view below. It appears as
several of the container’s hens have almost reached the end of
life-cycle, and are preparing to bloom. The light coloured
spherical structures on the tops of stalks are immature buds.
Before the buds appear, the
the lengthening stalk has the appearance shown below. At a
stage, the stalk’s leaflets will take on the normal purplish
Many immature buds push their
through the packed leaflets in the top section of the stalk.
In some cases the bud location
limited to the very tip of the stalk. By this point the
green colour has transitioned to purplish-green.
Notice the great variation in
size within a particular group. There is just a hint of
flowers’ final pink colour in a few of the larger buds.
A sequence of images taken
increasing magnification follows showing the buds at the top of
stalk shown at left.
Each of the buds is ringed by
green sepals which
sharply pointed tips. These sepals surround pink flower petals. The whorl of
referred to as the calyx.
the last few images, taken at the highest macrophotographic
magnification possible with my equipment, it is evident that the
on the sepal have bulbous red tips, which indicates that they
glandular in nature.
Eventually some of the buds
to bloom. A closer view of the flowers reveals that they
shaped like a star,
with about 12 reddish-pink petals. The most
characteristic of a flower is the ring of stamens arising from
at the base of the petals. Anthers are yellow in colour,
their supporting filaments are bright red.
arachnoideum ‘Forest Frost’ buds are strikingly
in form, and colouration!
“Of all the Houseleeks
Walter Ingwersen 1943
magnification shown below, it is apparent that both the
the flower’s petals are covered with fine hair-like
The whorl of pink petals is referred to as the flower’s corolla.
The petals of the flower grow
the edge of a yellow dome-shaped disk, and the male stamens grow
ring where the petals meet the disk. Emerging from the
itself is a group of bright red female pistils.
If the surface of a green
examined under the microscope, the subtle green colouration is
reminiscent of a pastel painting. Note that a water mount
used, and this accounts for the occasional bubble in the field
Near the edges of a sepal,
the glandular hairs seen earlier are visible. Notice that
colouration in the glandular, bulbous tips is localized in two
The use of a different
technique emphasizes the bulbous tips of the hairs, but does so
More images of flowers at
stages of development follow. Next, we will look at one of
flower’s pink petals with the aid of the microscope.
Photomicrographs of the
edge of a petal can be seen below. Its cells are
in shape, and pink colouration. Hairs growing along the
edge are visible in the second image.
A petal vein can be seen in
image on the left below. The image on the right reveals
presence of glandular hairs on the petal’s surface.
A higher magnification shows
longitudinal striations on the surface of individual cells (left
image), and the bulbous tips of glandular hairs (right image).
In the sequence of three
that follows, some of the anthers are covered by a thin purple
which hides the developing pollen grains beneath. In more
anthers this protective purple membrane has disintegrated.
Notice the unusual surface
of the anther at the centre of the left image. The image
shows a membrane that has split longitudinally to reveal the
underlying pollen grains.
When the membrane has
disintegrated and fallen away, the remaining anther appears
considerably smaller. Each anther has two pollen releasing
with a darker central section that is connected to the
This forms a sort of anther ‘sandwich’.
The slightest contact is able
dislodge pollen from the anther, as can be seen in an area where
has touched the surface of a petal.
Below are photomicrographs
the surface of a mature anther. The pollen grains can be
be ellipsoidal in shape.
Images showing pollen grains
adhering to the top of a filament (left), and the surface of a
(right), can be seen below.
Ten bright red pistils, each
connected at its base to a pale green swollen ovary are visible
centre of the flower shown in the two images that follow.
Under the microscope the
structure of the stigma and its supporting style can be seen
below. At the very tip of the pistil, the unusually short
that make up the surface of the stigma can be seen. In my
experience, these lobes are shorter than those in most flowers.
In the first image below, the
of one of a flower’s styles (red) is shown at the point of
to its associated ovary (green). Note, in all of the
large swollen heads of the glandular hairs.
Hens and chicks are extremely
popular as rock garden plants. This popularity has
resulted in an
amazing number of ‘common’ names being given to the them.
of them are: Houseleek, Jupiter’s Eye, Jupiter’s Beard, Thor’s
Bullock’s Eye, Sengreen, Ayron, Ayegreen, Aaron’s Rod, Hens and
Liveforever, and Thunder Plant!!
The low magnification, (to
macro-photographs were taken using a 13 megapixel Canon 5D full
DSLR, using a Canon EF 180 mm 1:3.5 L Macro lens.
A 10 megapixel Canon 40D DSLR,
equipped with a specialized high magnification (1x to 5x) Canon
lens, the MP-E 65 mm 1:2.8, was used to take the remainder of
The photomicrographs were
using a Leitz SM-Pol microscope (using a dark ground condenser),
the Coolpix 4500.
A Flower Garden of
A complete graphical index of
of my flower articles can be found here.
The Colourful World
A complete graphical index of
of my crystal articles can be found here.
Microscopy UK or their contributors.
Published in the
March 2012 edition of Micscape.
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