Rosaceae

In this series, I aim to give you a quick introduction to some of the common plant families found in the UK. Learning to identify plant families is a great help in identifying individual plant species you come across – if you know the family, then you know where to start looking for the species in a guide, and identifying the family is an achievement in itself. Plants are classified into families based on characteristics that they share; this is then narrowed down further into genera and then into species. So, the way to identify a plant’s family is to know these characteristic features.

In this video we are going to look at the Rosaceae, the rose family. This is a very diverse family containing around 2800 species. They are found throughout most of the world, although there are more in the Northern Hemisphere than the Southern. The majority are perennial, though there are some annuals, and they include trees, shrubs and herbaceous plants.

The Rosaceae is a very important family in terms of both food plants and ornamental plants. Apples (Malus domestica), pears (Pyrus communis), almonds (Prunus dulcis) and raspberries (Rubus idaeus) are all in this family. Ornamental-wise there are, of course, roses (Rosa species), but also Cotoneaster, firethorn (Pyracantha), cherry laurel (Prunus laurocerasus) and lady's-mantle (Alchemilla mollis). Rose essential oil extracted from flower petals is used in cosmetics and a number of species are used in traditional medicine. Wild species in the UK include trees like hawthorn (Crataegus monogyna), rowan (Sorbus aucuparia) and blackthorn (Prunus spinosa); shrubs like bramble (Rubus fruticosus agg.) and dog rose (Rosa canina); and herbaceous plants like meadowsweet (Filipendula ulmaria), wood avens (Geum urbanum), tormentil (Potentilla erecta) and Alpine strawberry (Fragaria vesca).

The flowers of the Rosaceae have a distinctive look - they are open, symmetrical in more than one plane and usually have five petals and five sepals, although there are some species with four. The petals come in a whole variety of colours, though many are white or yellow. They have many stamens and varying numbers of carpels (the female parts of the flower).

In a lot of Rosaceae species the base of the flower forms a structure called a hypanthium - a floral cup that encloses the carpels and to which the petals, stamens and sepals are attached. Collectively, the sepals are known as the calyx. Many species also have an epicalyx, which is like an extra set of sepals. This makes it look as though the flowers have 10 sepals, rather than five, but if you look closely you might be able to see that there are two rings of five. The majority of these plants are pollinated by insects, frequently bees.

This family produces a diverse array of fruits that may be dry or fleshy, that may split open to release the seeds or not split. Some, like cherries (Prunus species), have flesh surrounding a single seed; others, like roses, have a collection of seeds in a fleshy hip; in raspberries and blackberries each seed has its own fleshy surround. These have evolved to be eaten and dispersed by birds and other animals. Wood avens has dry, hooked fruits that catch on fur and clothes. Other species have fruits and seeds that are dispersed by wind.

The leaves of Rosaceae can be simple (undivided) but are often compound: divided into leaflets. The leaf margins tend to be serrated. There are structures called stipules at the base of the leaves, paired and leaf-like. The leaves are arranged alternately on the stems, and the stems may have thorns or prickles on them.

So, a plant with open, five-petalled flowers with lots of stamens, that have a hypanthium (floral cup) and an epicalyx, and that has compound leaves with serrated margins, that are arranged alternately on the stems, is probably going to be in the Rosaceae.

Have a look for the three species when you are out and about:
Meadowsweet (Filipendula ulmaria)
Wood avens (Geum urbanum)
Bramble (Rubus fruticosus agg.)


[Note, botanical names should always be written in italics (or underlined if handwritten)]