Five-minute families - Apiaceae

Learn how to identify common plant families in (more or less) five minutes.

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.

Today we’re going to look at the Apiaceae: the carrot family. This family is also known by its older name of Umbelliferae, named so for the structure of their flowerheads.

There are around 3500 species of Apiaceae, found throughout the world but predominantly in temperate areas. The majority are herbaceous, with a few shrubby species, and they may be annuals, biennials or perennials.

This family includes many species we use for food and as herbs and spices, like carrot (Daucus carota), celery (Apium graveolens), coriander (Coriandrum sativum) and parsley (Petroselinum crispum). Ornamental species include sea holly (Eryngium), sweet Cicely (Myrrhis odorata) and fennel (Foeniculum vulgare). Dill (Anethum graveolens), aniseed (Pimpinella anisum) and several others can be used medicinally. It should be noted, however, that this family also contains species that are toxic - some quite impressively so, like hemlock (Conium maculatum) and hemlock water-dropwort (Oenanthe crocata). Giant hogweed (Heracleum mantegazzianum) and wild parsnip (Pastinaca sativa) contain chemical compounds in their sap that cause burns on skin when exposed to sunlight. Some wild plants in the Apiaceae are cow parsley (Anthriscus sylvestris), common hogweed (Heracleum sphondylium), ground elder (Aegopodium podogaria) and sanicle (Sanicula europea).

The species found in the UK are herbaceous and variously annual, biennial or perennial.

The distinctive flowerheads, or inflorescences, of the Apiaceae are called umbels, hence their alternative name of Umbelliferae. These umbels are relatively flat-topped clusters of flowers that radiate out from a central point to form an umbrella-like shape. The inflorescences are often compound umbels: an umbel shape made up of many smaller umbels. The umbels may have bracts or bracteoles beneath them, which protected the flowers in bud. Whether they have bracts or not is an important identification character.

The individual flowers in these umbels are small and normally regular in shape (symmetrical in more than one plane) though the flowers on the outside of the umbels sometimes have larger petals on their outer edges. Flowers have 5 petals with the sepals either much reduced or absent altogether. The petals are white, sometimes pink-tinged, or yellow. Each flower has 5 stamens and 2 stigmas. These stigmas are attached to a swollen base called a stylopodium. The flowers are pollinated by a range of insects.

The ovary of the flowers is inferior (attached to the rest of the floral parts) and develops into a dry, ridged fruit that splits in 2 once ripe. The stylopodium is visible on the fruits. The size, shape and ridging of the fruits can be important for the identification of species.

The stems of Apiaceae are often, but not always, hollow, and tend to give the plants a leggy look.

The leaves are arranged alternately up the stems and have bases which sheath the stem.

The leaves are lobed or divided, often into fine leaflets, giving many species a delicate appearance. The upper and lower leaves may have quite a different appearance. The plants are frequently aromatic.

So, a plant with whitish or yellow flowers arranged in umbels, that develop into dry fruits with ridges, and that has divided leaves with sheathing bases, that alternate up the stem, will probably be a member of the Apiaceae family.

Have a look for these 3 species on your travels:
• Sweet Cicely (Myrrhis odorata)
• Ground elder (Aegopodium podogaria)
• Common hogweed (Heracleum sphondylium)

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