A Close-up View of the

Dotted Hawthorn

Crataegus punctata

by Brian Johnston   (Canada)

“The beautiful Hawthorn, that has now put on
Its summer luxury of snowy wreaths,
Bending its branches in exuberant bloom,
While to the light enamour’d gale it breathes,
Rife as its loveliness, its rare perfume.
Glory of England’s landscape!  Favourite tree
Of bard or lover!  It flings far and free
Its grateful incense.”

“Forest Minstrel”
William Howitt

The tree which is the subject of this article grows about 300 metres from my home.  As the poem suggests, it is simply beautiful when it blooms in the spring, as it provides a huge abundance of brilliantly white flowers.  Neither I nor my neighbours however could, by any stretch of the imagination, agree with the poet about “Its grateful incense”.  I suppose that it depends on what is meant by the term “rare”, as in “rare perfume”.  The tree in question does flood the entire neighbourhood with its scent.  Unfortunately the scent is best described as foetid, and closely resembles decaying fish!  Passersby tend to hold their breath when walking nearby.

Hawthorns are deciduous members of the Rose family (Rosaceae) which normally possess spines.  The genus name Crataegus is derived from the Greek, and translates to ‘flowering thorn’.  The species studied here, punctata, refers to the unusual dots which cover the tree’s fruit, and which are actually glands.  The common name Hawthorn is derived from ‘haw’ which is the old English name for a hedge.  Thus Hawthorn refers to a ‘thorny hedge’.

Pictures of the tree in question follow.  It’s about 6 metres in height and has the same width.  Its crown is roughly rounded, with spreading branches.  Since it is obviously a Hawthorn, I was puzzled by the fact that no spines were visible anywhere.  Investigation revealed that Crataegus punctata has fewer spines than most other Hawthorns.  In fact a thornless cultivar is sold in North America, and I suspect that the City deliberately chose this cultivar to prevent puncture accidents, since the tree grows beside a sidewalk.

The bark is grayish-brown in colour, and is scaly.  Lighter coloured areas are patches of lichen.

Strangely, the tree’s buds are pink in colour, and this colour fades to white as the flowers bloom.

The series of images that follows show the Dotted Hawthorn’s flowers.  Most of the colour is provided by the bright red, immature anthers.  Notice that in newly opened flowers, these anthers are arranged in a ring around the central pistils.  Later, the filaments lengthen, and the stamens spread to take up more random positions.  The flowers themselves are arranged in corymbs, in which the stalks are of varying length, producing a flat topped cluster.

When flowers bloom, their anthers are covered by a bright red membrane which protects the developing pollen grains.  Their supporting filaments are curved, and white in colour.  Each flower possesses about twenty stamens, and from two to five styles.  This particular cultivar has two.

The series of images that follows shows, with increasing magnification, these membranous anthers and their filaments. Notice in the first two images that a flower has five irregularly shaped, white petals.

As time passes, the red membranes begin to disintegrate, revealing the less visually appealing , brown, pollen shedding anthers beneath.  (The process of an anther’s releasing pollen is referred to as dehiscing.)  The difference in size of the ‘red’ anthers, and ‘brown’ anthers is striking!

Closer views of pollen releasing anthers reveals that they possess two pollen covered pads on either side of a dark central disk, which is attached at its base to the filament.

The later stages of a blooming corymb are much less colourful than the early ones.  Without the bright red membranes, flowers have a rather drab appearance.

Twigs are grayish-brown in colour.  Notice the complex series of rings at several locations on the twig.

Immature fruit, (more correctly called pomes), of the Dotted Hawthorn are indeed ‘dotted’ with tiny white glands.  (A pome is a fruit with fleshy outer tissue and a papery-walled inner chamber containing the seeds.)  Although eventually they will have a dull red colour, at this early stage they are light brown.

Notice that a leaf’s margin is finely serrated, and that it has a complex vein pattern on its upper surface.

Although Dotted Hawthorn flowers have an extremely unpleasant scent to humans, the smell is positively delightful to midges and they are strongly attracted to it.  For this reason midges are the main instrument of pollination in the wild.

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.

An 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.

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 August 2012 edition of Micscape.
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