When the blackthorn is in bloom, spring is definitely
heralded, preceding by a couple of weeks the more showy blossoms of the
cultivated cherries (also genus Prunus)
in towns. My previous two studies have
been of families of monocotyledons and so a change to a dicotyledonous family
is due as I explain more botanical terms in a straightforward way.
Prunus is the Latin word for plum tree, while spinosa refers to the spines that are present. These spines are often quite difficult to
find, but you can find shoots that have long spines extending from the dark
brown to black woody shoots.
The flowers open before the leaves in the spring, but the
flowering period is quite long so in a few weeks there will still be flowers
along with leaves on the shoots.
The flowers of the blackthorn are produced on the previous
years’ shoots and arise very close to the main stems on short side shoots. These shoots have a bud at the tip which
opens to reveal leaves (vegetative bud) and the
flowers arise from the base of the bud.
There may be one, two or three arise from the same level.
There are five white sepals
at the end of the pedicel (flower stalk) and
five white petals. These are called sepals and
petals because they differ greatly in structure and colour. The five sepals together are collectively
called the calyx and the five petals together
are the corolla.
The sepals are not attached to one another and are described as being free. The same is true for the petals. There are 20-25 stamens
and these consist of long white filaments and
small yellow anthers, turning orange and then
brown. In the centre of the flower is a
single green style with a single yellow stigma.
The stigma is rounded (termed capitate).
In between the base of the filaments and the style is a glistening area which
is an indication of nectar.
If the flower is cut
in half with a blade it becomes clear that the sepals, petals and stamens are
all attached to the top of a cup-shaped structure which has the ovary attached
at its base. This structure is called
the receptacle. In other flowers this may be
flat or of other forms but this cup-shape is quite common in the rose
family. The colour of this cup shape is
golden and glistening and has glands on the surface producing nectar; it is described
as being a nectariferous disc. The stamens, petals and sepals aren’t
attached to the top of the ovary or below the ovary, but rather on the rim
around it. This arrangement is called perigynous (peri = around; gynous = female parts). The ovary however is described as being superior as it is itself attached to the base of the
receptacle. If it is cut across, it can
be seen there are two ovules in the ovary. They are attached to the top of the ovary and
are said to be pendulous.
After fertilisation
one of the ovules aborts and the ovary swells into a spherical fleshy fruit
containing a single stony seed. A fleshy
fruit of this type with a hard stone in the middle is called a drupe. The fruit matures from green to dark blue with
a whitish “bloom” that comes off when rubbed with a finger. These are the
familiar sloes, collected for jam and gin.
No comments:
Post a Comment