A Close-up View of a

Mullein Hybrid

Verbascum hybridum 'Caribbean Crush'

by Brian Johnston   (Canada)

Common mullein (Verbascum thapsis), the subject of an earlier article, is an ubiquitous wildflower, and its tall woolly spikes, covered with bright yellow flowers, are easily recognizable.  I thought that it might be interesting to take a photographic look at an exotic relative produced by modern hybridization techniques.  This article is the result.

Verbascums, or mulleins as they are sometimes called, are native to the Mediterranean region, but many have become naturalized throughout North America.  All belong to the Figwort family, (Scrophulariaceae).  It is believed that Mulleins have been grown as a garden flower since the medieval period, and much work has been done to “improve” the lowly wildflower, by judicious use of modern botanical techniques.  One such cultivar is the subject of this article, Verbascum hybridum ‘Caribbean Crush’.  Although the plant is undeniably spectacular, it doesn’t live up to the developer’s original advertising, which stated that “the stalks are covered with flowers that range from burnt orange to yellow or mango.”  In reality, all of the flowers on a stalk have exactly the same colour!  (It was ever thus!)

The tip of a 70 centimetre long stalk can be seen below.  Although in general, the flowers bloom from bottom to top, there are exceptions.  Unopened buds are present both above, and below the flowering section.

As the buds mature, they change colour from green, through yellow, to red.  At an earlier stage (farther up the stem), the extremely hairy, pointed green bracts (modified leaves) that enclose the buds, predominate the view.

Even the under-surfaces of the developing flowers’ bud-stage petals have a liberal coating of fine white hairs.

As the buds mature, their stalks grow longer.  Notice in the image at left, that very immature buds are mixed in with their older siblings.  Near the top right of the image on the right, a flower has completed blooming, and all that remains is the long pistil ringed by sepals.

At the centre of the image below, note the pointed shape of an early stage bud.

Notice in the two images that follow, how the flower’s petals are folded over one another in an almost random manner, with each bud showing a different fold pattern.

Here are several images that show the purple style, and green stigma that remain after the petals of a flower drop off.  Once a flower has bloomed, this petal-drop happens extremely easily.  The slightest touch of the stem produces an alarming shower of petals – (alarming to the person trying to photograph “perfect” flowers that is!)

The image below shows a bud with a pentagonal shape, about to blossom.

Buds in the process of opening can be seen in the lower portions of the two images that follow.

Multiple stems grow from the plant’s base.  Notice the different flowering pattern exhibited by each stem.

Once opened, the five-petaled, 2.5 centimetre diameter flowers are revealed.

If the base of one of the flower’s petals is examined under the microscope, a variety of pigmented, and unpigmented cells can be seen.

On the underside of a petal, hairs grow from the surface.

The surface (epithelial) cells of a petal are almost spherical in shape.  (Adobe Photoshop’s “Auto levels” function was used on both images to increase contrast.  This accounts for the false colouration.

A higher magnification view of a petal’s underside shows that the hairs growing from its surface are branched.  Contrasting with these hairs, are the ones growing along the edge of the petal, some of which have glandular protuberances at their tips.

The three images that follow show views of the flower’s strange reproductive structures which consist of a single pistil, and five stamens.  In this species, three of the stamens are smaller, and are fringed with long white hairs, while two are larger, and are less hairy.

The distinctive differences between the two types of stamen can be seen clearly in the higher magnification image that follows.  The three smaller anthers, (male pollen producing structures), have a yellow base, and a brownish-red edge.  Immediately beneath each anther is a dense fringe of white hairs.  The lower two anthers are larger, and are missing the hairy fringe.  If you look carefully however, you can see that the red filaments supporting the anthers have their own white surface hairs.

All of the white hairs mentioned above have bulbous tips.  Those on the filaments tend to have red bulbs, while those on the upper anthers tend to have white bulbs.  Three images showing filament hairs can be seen below.

As the hairs age, they tend to become ribbon-shaped, and have the random, twisted appearance seen on the right.

Below, on the left, is a photomicrograph that shows the darker coloured band at the edge of an anther.  The higher magnification image on the right shows the cellular structure of an anther’s surface.

Several hairs from an anther’s fringe can be seen below.  The colouration doesn’t appear white because the light from the dark-ground condenser has been coloured by passing through the anther itself.

The four images that follow show different views of a flower’s pistil,  consisting of a red supporting style, and green stigma (pollen accepting organ).  In this species the stigma has a flattened oval shape, with a distinctive groove on its upper surface.

Under the microscope, this groove can be seen clearly.  Notice that the stigma’s entire surface is covered with tiny, hair-like protuberances.

These protuberances are easier to see in the higher magnification images that follow.  Their purpose is to increase the effective surface area of the stigma, and aid in the retention of pollen grains carried to the flower by visiting insects (usually bees).

Like the common mullein, this hybrid has intensely hairy leaves, and this causes them to feel downy soft to the touch.  The lighter coloured veins on the leaves’ lower surfaces gives them a very attractive appearance.

The leaves are stalkless – they grow directly out of the main stem.  Note that the stem is also covered with short, soft, white hairs.

In contrast to the lower surface, the upper surface of a leaf has far fewer hairs, and in the right light, appears shiny.

Closer views of the bottom of a leaf reveal that every part of the surface is hairy.

The two images that follow show the segmented nature of the hairs growing along a leaf’s edge.

If the hairs growing from the veins on the under-side of a leaf are examined, they appear to branch, and have pointed tips.

Much shorter, glandular hairs, that end in bulbous tips, grow from a vein’s surface.  The image on the right shows their circular top when viewed from above.

The striking flowered spikes of Verbascum hybridum ‘Caribbean Crush’ make this plant a popular garden choice.  Like its lowly relative Verbascum thapsis, it does best in poor, dry, rocky soil.  When watered or fertilized too much, it grows poorly.  What more could a gardener ask for?

Photographic Equipment

All of the macro-photographs were taken with an eight megapixel Canon 20D DSLR equipped with a Canon EF 100 mm f 2.8 Macro lens which focuses to 1:1.  A Canon 250D achromatic close-up lens was used to obtain higher magnifications in several images.

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

Further Information

A search for “Verbascum  information” using Google results in a wealth of info, both on the wildflower, and hybrid species.

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 July 2009 edition of Micscape.
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