Close-up View of a 'Hen and Chicks' Hybrid Sempervivum tectorum 'Red'


A Close-up View of a

'Hen and Chicks' Hybrid

Sempervivum tectorum 'Red'

by Brian Johnston   (Canada)

Sempervivums are extremely hardy, mat-forming succulents of the family Crassulaceae, commonly known as ‘Hen and Chicks’ or ‘Houseleeks’.  Native to the mountains of Europe, the Middle East, and Central Asia, they grow close to the ground, with fleshy leaves grouped around one another in a very tightly packed rosette.  The ‘hen’ is the main plant, and the ‘chicks’ are the offspring, which start as tiny buds on the main plant, and soon sprout their own roots, taking up residence close to the ‘hen’.

Hens and chicks have a very long history of cultivation.  It is said that the Frankish King Charlemagne (742-814 AD) suggested to his subjects that they grow the plant on their thatched roofs in order to guard against fires caused by thunderbolts, storms and sorcery.  Since succulents do retain water in their leaves, they may help in the first two cases, but as to sorcery – perhaps not!

The genus name Sempervivum is Latin for ‘always alive’ (evergreen).  Tectorum, the species name is also Latin, and translates to ‘on roofs’.  Thus – the plants live for extended periods on rooftops.

Anyone growing hens and chicks knows that there is a small ‘fly in the ointment’ however.  Most Sempervivums are monocarpic, meaning that a particular hen flowers only once, and then it dies.  Fortunately by the time that this happens (usually several years), it has already produced many chicks to take its place.  I was fortunate to obtain at my local greenhouse, a striking cultivar that had a single hen in the process of flowering.  This article is the result.

The first image in the article shows a few of the beautiful pink, star-shaped flowers that cover the blooming stalk.  The series of images below shows the beginning of the flowering process.  Notice that the hen, which originally was a tightly packed rosette of leaves, has extended upward an amazing distance (about 20 centimetres at this point).  Hidden behind the fleshy leaves is a 1.2 cm diameter stalk, and at the point where each leaf joins the stalk, a group of buds extends out on its own stem.  Only a few of the buds have opened to reveal flowers.

Closer views of the flowers reveal that they are (actinomorphous), shaped like a star, with about 15  pinkish-white petals.  The most noticeable characteristic of a flower is the ring of stamens arising from the disk at the base of the petals.  Supporting filaments are bright red in colour.  Depending on whether they are immature or mature, anthers appear pinkish-red, or bright yellow.  This phenomenon will be discussed in more detail later in the article.

It is simply amazing how the tightly packed leaflets at the top of a hen rosette are suddenly carried aloft by the rapidly growing stalk of the plant.  Near the top of the stalk, clusters of pale pink, furry buds grow out from the gaps between the leaflets.

Closer examination of one of the leaflets reveals its cellular structure, and the closely spaced needle-like hairs that ring its edge.

Each of the buds is ringed by many green sepals which have pink, sharply pointed tips.  These sepals surround the pink flower petals that extend beyond them.

As we move closer to the buds, it becomes apparent that the surfaces of both sepals and petals are remarkably hairy.  Most hairs are colourless, which increases their visual contrast with the green sepals and pink petals.  Close examination also shows that at a very early stage, the sepals are pinkish in colour, and only later does their green colouration develop.

If you look carefully at the tips of the sepals in the two high magnification macrophotographs that follow, you can see the strange, bright red, bulbous structures, each of which has a ring of colourless hairs arranged radially in a planar configuration.  How strange!

Over a period of several days, buds begin to open.  The two images below show this process at an early stage.

To give some perspective, here are two images that show the entire group, consisting of a hen and its off-shoot chicks, that was the subject of this article.  At this point, the accumulated weight of the leaflets, buds and flowers has become so great that the hen’s stalk has begun to bend alarmingly.  At no point however, did the stalk give way.  The first image gives a clue to the inevitable future of the hen, as the bottom-most leaflets have already begun to turn brown.

A view of the ‘back’ of the main stalk reveals its cylindrical, light green structure.  Note that the base of a leaflet grows directly from the stalk.  Also note the narrower diameter of one of the stalks supporting a cluster of buds.

Here is a group of images showing some of the ‘chicks’ that surround the blooming ‘hen’.  Notice the sharply pointed tip of each leaflet.

Higher magnification once again reveals the closely spaced, tiny hairs that grow from the edge of a leaflet.

Once the plant begins to bloom, the resulting flowers are remarkably long-lived – up to two weeks!  The top of the stem is abundantly covered with blooming flowers and buds, producing a stunning, and unusual display.

Now lets ‘zoom in’ on the top of the stalk in order to see the profusion of colourful, star-shaped flowers.

The flower in the lower left corner of the image below has just opened.  Notice that the two rings of anthers are deep reddish-pink in colour.  At the centre of these rings is a group of hair-like, purple protuberances that are, in fact, the flower’s pistils.  By contrast, the flower in the upper right corner of the image opened several days earlier.  Here the anthers are bright yellow, with a deep purple furrow bisecting each into two lobes.

In some areas,  all of the flowers’ anthers are releasing bright yellow pollen.

In the flower shown at left below, all of the anthers are covered by a thin purple membrane which hides the developing pollen grains beneath.  In the image on the right, half of the protective purple membranes have disintegrated, revealing yellow pollen releasing anthers.  Notice in both images, the hairy tips of the flower’s petals.

Under the microscope, the details of these petal tips are easier to resolve.  Many pollen grains adhere to the colourless hairs that cover the tip’s edge.

A higher magnification shows that the pollen grains are ellipsoidal in shape.

Although it is difficult to see, the surfaces of  petals are also covered by hairs.  Several of these can be seen to have bulbous tips in the lower left half of the image.  The bulbous tips imply that the hairs may be glandular in nature.

Additional images showing these glandular hairs can be seen below.

Still higher magnification shows the structure of the base of the hairs.

Each of the plant’s flowers has a diameter of about 2.5 cm.  What does its supporting stalk look like?

The answer can be summed up in one word – hairy!  Extremely fine, and remarkably soft hairs, result in the stalk feeling downy.

Let’s look more closely at the flower’s stamens.  As mentioned earlier, when the flower first opens each anther’s exterior surface is covered by a thin pinkish-red membrane.

The membrane appears to be bisected by a lighter band that can be seen in the image below.

Closer examination using a microscope however, reveals that some of the membranes are divided into four quarters by two longitudinal bands.  Most however, are simply bisected.

The cells composing the lighter bands are larger than those that make up the rest of the membrane.  When the membrane begins to disintegrate, the process starts along these lighter bands.

Pollen grains from mature anthers in the vicinity have ‘stuck’ to the surface of one of the membranes (left image), and to the anther’s supporting filament (right image).

The two images that follow reveal the moment when an anther’s membrane begins to split longitudinally along the band.  A copious quantity of bright yellow pollen is then revealed.

In the flower shown below, only one of the anthers has begun to expose its pollen, and if you look closely, a small segment of the purple membrane still remains in its upper left-hand corner.

The membrane disintegration process has happened to a greater degree in the flowers shown in the images that follow.  Strangely, the dark, deep purple bisecting band in each of the mature anthers started out as the lighter coloured band in its immature stage!

At the centre of the circle formed by the flower’s stamens, there is a group of what look like deep purple hairs.  These are the female pistils of the flower.

Under the microscope, a pistil can be seen to have a white tip – the stigma.  Beneath the stigma is its bright red supporting style.  The image on the right shows a group of pollen grains that have adhered to the pistil’s surface.

Even the lighter coloured base of the style is pollen covered (left image).  Higher up the style (right image), its surface has been damaged, allowing us to see the long, thin cells of which it is composed.

Here all but three of a flower’s anthers have fully matured.

The final stage of the blooming process shows all of the anthers mature.

One of the flower’s petals can be seen in the two images that follow.  Notice on each side at its base, the brilliant red globular tips of two of the flower’s sepals.

Even at the high macrophotographic magnification of the image on the right below, it is not really possible to distinguish individual pollen grains.

Under the microscope, using low power, it is still difficult to resolve single grains.

At much higher magnification however, their ellipsoidal shape becomes apparent.

The seeds produced by the flowers of a particular Sempervivum plant can be used to grow another, however they usually do not breed ‘true’ to their parentage.  New variations are often produced in this way. 

Vegetative reproduction occurs when the hen ‘offsets’.  Here, the base of the hen produces what look like thin, root-like stems called stolons with tiny chicks at their 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 family group.  Vegetative reproduction produces offspring with the same characteristics as the parent plant.

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.  A few of them are: Houseleek, Jupiter’s Eye, Jupiter’s Beard, Thor’s Beard, Bullock’s Eye, Sengreen, Ayron, Ayegreen, Aaron’s Rod, Hens and Chicks, Liveforever, and Thunder Plant!!

Photographic Equipment

The low magnification, (to 1:1), macro-photographs were taken using a 13 megapixel Canon 5D full frame 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 macro lens, the MP-E 65 mm 1:2.8, was used to take the remainder of the images.

The photomicrographs were taken using a Leitz SM-Pol microscope (using a dark ground condenser), and the Coolpix 4500.

A Flower Garden of Macroscopic Delights

A complete graphical index of all of my flower articles can be found here.

The Colourful World of Chemical Crystals

A complete graphical index of all of my crystal articles can be found here.

 All comments to the author Brian Johnston are welcomed.

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Published in the February 2012 edition of Micscape.
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