This
genus was formerly placed in its own family (Aceraceae) with genus Dipteronia). Recent research including molecular studies
suggests that a broadly definition of Sapindaceae is more logical than
separating Aceraceae. The Flora of China
separates Aceraceae as a separate family while Stace (2010) unites the families.
The name Acer is the classical Latin name for the
maple. The species name platanoides refers to its similarity to
the plane tree (genus Platanus).
The flowers arise from terminal
buds, appearing towards the end of March into April. The flower stalk has short unfolding leaves
at its base. The flowers are arranged in
panicles which form a rounded, upright cluster.
Each subsection of the panicle has the stalks at different lengths
meaning the flowers and buds are more or less level with one another. This means the inflorescence could be
described as a compound corymb. The
lower branches are opposite one another and have a narrow bract each side. Subsequent branches have shorter to very
short bracts grading to none at all towards the end of each subsection.
Each
panicle either contains male flowers or female+male flowers on the same
tree.
Male flowers
The
flowers have a central swollen quoit-like disc and the stamens are attached in
the tissue of the disc. The sepals and
petals are attached under the disc.
There are five sepals
which alternate with five petals. The
sepals are just about joined to one another at the base and arise from the conical
receptacle at the top of the flower stalk.
They are tongue-shaped with wavy margins and with the tip weakly lobed. From above they can be seen to have several
more or less parallel veins. A few
silvery hairs arise from the clefts between the sepals.
The five
petals consist of an elongate oval section (the blade) and a stalk-like basal
section (the claw) which attaches it under the disc. From above the oval section is pinnately
veined.
There are eight
stamens; the anthers are borne on long filaments. The filaments are attached to the back of the
anthers and they open to expose pollen towards the middle of the flower.
The
centre of the disc is deeply hollowed and a white oval to quadrangular
structure is present at the bottom of the hollow. This probably represents the non-functional
stigma. When sectioned there are no
structures differentiated below this, within the receptacle.
Hermaphrodite flowers
These
flowers also have a central swollen quoit-like disc and the stamens are
attached in the tissue of the disc. In
this case however, the stamens do not appear to be open and thus the flower is
probably functionally female. If broken open it will be found that they do
contain pollen – I’m uncertain if this is viable. The sepals and petals are attached around the
edge of the disc just under it. The top
photograph shows the flower with a sepal and two of the petals removed.
The arrangement and
shape of the sepals and petals are as in the male flowers, however there are no
hairs between the sepals.
There are
eight stamens; the yellow anthers are borne on short green filaments which
curve towards the middle.
The female part of the
flower arises from the centre of the disc.
The central part is swollen and bears two narrower triangular lobes, one
each side. There is a single style which
divides into two stigmas which curve outwards.
If the ovary is sectioned it will be found to contain two sections
(locules) separated by a central wall (septum).
Each locule contains two ovules one on top of the other each attached to
the septum.
The male
flowers seem to appear a couple of weeks earlier and then fall leaving a few
hermaphrodite flowers on the same panicles.
By this time the leaves are much more open.
