Buxus sempervirens is a rare native plant in southern England
growing in scrub and woodland on chalk. It
is a shrub or small tree. However it has
been very widely planted throughout Britain being useful as a short hedge and it
responds very well to topiary. It is in
flower in the spring. The genus name Buxus is of Classical origin. The species name sempervirens is a combination of the Latin semper = always and virens
= flourishing, referring to the perennial nature of the plant.
The leaves are small
and are much darker in colour on the upper and lower surfaces. Leaves are narrowly to broadly elliptic, with
a cuneate base and an obtuse or emarginate tip.
The margins are evenly rounded = entire. The midrib is the only vein visible from
above and stands slightly proud from the surface. The same is true for the lower surface where
the midrib shows up paler and under a lens it is marked by tiny white elongated
dots. The flowers are produced in the
spring.
There are three main sexual arrangements for flowers:
a) Flowers
have both male and female parts and both these are functioning, the male parts
producing viable pollen and the female parts ovules which can develop into
seeds. This condition is called hermaphrodite.
That has been the case in the previous four species considered in this
blog series.
b) Flowers
male or female with male flowers and female flowers occurring on the same
plant. This is called monoecious.
c) Flowers
male or female with male flowers and female flowers occurring on different
individual plants. This is called dioecious.
There may in some cases be a mix of hermaphrodite flowers
and single sexed flowers on the same plant or other combinations.
The flowers in box
are monoecious.
They are in tight groups in the axils of the leaves. Groups of flowers are called inflorescences. The flowers do not have stalks so this
arrangement is called a spike. Because
the flowers are so close together they are in a contracted
spike. The flowers at the base of
each group are male and more conspicuous due to the yellow anthers. Some spikes
(particularly those towards the tip of the flowering shoots) have a female
flower, which is green and has a much chunkier appearance.
This photograph shows
what you see if all the male flowers from a spike are removed except for
one. There are four stamens with white
filaments and yellow anthers. The
anthers open towards the centre of the flower thus they show introrse
dehiscence. There are four perianth
segments around the base of the stamens and they are free from one
another. In addition there is a small yellow
domed structure in the centre of the flower which is “pretending” to be the
female part of the flower. Because it is
not functional it is termed a pistillode.
A dissected out
female flower is photographed here. It
has six perianth segments which are separated from one another around the base and
which lie against the surface of the ovary.
They are green with pale margins.
The ovary is globular with three styles.
The stigmas are flat to concave surfaces on top of the styles. This arrangement implies that there are three
carpels united together each with its own stigma. This is called a syncarpous
ovary. If the ovary is cut
through with a blade it will be found to consist of three sections. 
Each section contains two ovules side by side
which are attached at the top of the ovary.
The surface between the styles is slightly domed and has a sheen - it
produces nectar and is called an interstylar nectary. After fertilisation the ovary swells and
becomes woody, retaining the styles which then appear as horns. These are seen in the top photograph.
The floral formula of the flowers is
In shorthand this would be written. Flowers unisexual. Male flowers with four free perianth segments
and four anthers. Female flowers with
six free perianth segments and three fused carpels.
The other species of family Buxaceae you are likely to find
is Pachysandra terminalis which is
widely planted as a ground cover plant.
It also flowers in the spring.
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