Acer platanoides. An example of family Sapindaceae

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.

Corylus avellana - a typical species of family Betulaceae

The name for each higher group in the classification of plants up to the order level is derived from one of the genera it contains.  This genus is termed the type genus.  Corylus and a few related genera used to be classified in family Corylaceae but have now been transferred to Betulaceae as subfamily Coryloideae.  Corylus avellana (hazel) was first named as such by Linnaeus in 1753.  Corylus is the classical Latin name for the hazel which has a distribution right across Europe and western Asia, except for the far north and some islands.  The English names for the species include hazel, hazelnut and avelline. The first recorded use of the species name was by Pliny the Elder in his Naturalis Historia, from Avella, a town in Italy.  It was later used by Leonhart Fuchs in his De historia stirpium commentarii insignes (1542) in which he uses the name Avellana nux sylvestris (the wild nut of Avella). 

The text from Linnaeus (1753) is as follows:

The male flowers of the hazel are a conspicuous feature of the countryside from late December onwards.  They are borne on long thin catkins; because they bear male flowers only they are termed staminate catkins.  These have a short stalk and then a central rachis to which the individual flowers are attached spirally.  Each flower has a hooded pale creamy-green bract with the stamens underneath.  The bract is pointed in the middle and is fringed with short, pale, curly hairs.  With magnification it can be seen that there are two further structures under the bracts – these are the bracteoles and they are attached to the outer half of the bracts; they are also fringed with curly hairs.  The stamens are attached to the underside of the bract at about the same point as the bracteoles.  The bracts taper to the rachis so it is difficult to decide whether the whole catkin is a raceme (each flower with a stalk) or a spike (each without a stalk).  There are six stamens in the upper part of the bract and two arising from the narrowed part of the bract, nearer its point of attachment to the rachis.  The six upper stamens form three pairs and one or more of these may have their filaments joined near the base.  In all the flowers inspected the basal pair of stamens have their filaments joined.

The number of flowers under each bracts as well as the number of

The female flowers are inside a bud-like structures which are further back on the branches than the male ones.  The bud scales towards the base are green and fringed with pale hairs.  The length of the fringe hairs is longer on the scales further inside and these also have an increasing amount of silvery hair on their outer surface.  From the tip of the bud there are a number of stigmas.  Early on these are bright red and then they fade to a purple-brown.  On the ones I inspected there were 18-20 stigmas.  Hayward (1987) in his New Key to Wild Flowers, page 138 wrongly states “the female flowers look like tiny buds with 2 red styles”

  

If the outer scales are removed, a central section is isolated, consisting of narrow hairy bracts and the stigmas.  If prised apart and carefully examined the stigmas are in pairs and each bract has two pairs of stigmas associated with it and a pair of smaller unequally-sized bracteoles.  It is very difficult to see this as the flowers are so closely associated.  If the bracteoles have dried a bit, some can be seen as having an uneven outline as two triangular lobes.  At the base of the stigmas is a small ovary which is divided into two ovules.  Each flower therefore has four stigmas (two per ovule) and thus the whole structure contains five flowers (= 20 stigmas).  There is no clear distinction between stigma and style.  The surface of the style is minutely papillose (uneven with microscopic rounded bumps).  The Flora of China (1999) volume 4 interprets the structures as each ovule having a single style which is divided to the base.

The Flora Europaea makes reference to a small irregularly-lobed perianth in addition to the bracts and bracteoles as does Stace (2011) but I could see no further structures apart from the silky hairs on top of the ovary.