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 Lamiaceae, the mint family or dead nettle family. This family is still sometimes called the Labiatae, an older name that refers to the flower structure of the plants. Members of the Lamiaceae are found almost all around the world and there are more than 7000 species. They include both annuals and perennials and are mostly herbaceous plants or shrubs.
The Lamiaceae contains a huge number of species we use as medicinal and culinary herbs, like mint (Mentha spicata), rosemary (Salvia rosmarinus), basil (Ocimum basilicum) and sage (Salvia officinalis). We use them as garden plants and for wildlife, like lavender Lavandula angustifolia, catmint (Nepeta cataria), Coleus and the variegated cultivar of yellow archangel (Lamiastrum galeobdolon subspecies argentatum), which is a common garden escape. Wildflowers like white dead-nettle (Lamium album), selfheal (Prunella vulgaris), ground ivy (Glechoma hederacea) and water mint (Mentha aquatica) are in this family.
In the UK there are about 60 species of Lamiaceae, generally herbaceous perennials or annuals.
The flowers of Lamiaceae are zygomorphic, meaning they are only symmetrical in one plane, unlike, say, a daisy, which is actinomorphic - symmetrical in more than one plane. The petals are fused to form a tube with an upper lip and a lower lip at its end. The upper lip usually has two lobes and the lower lip has 3 lobes. Lamiaceae species are insect pollinated and the lower lip provides a landing platform for insects like bees. There are normally four stamens and two are often longer than the others (or two are often shorter than the others, depending on your point of view). The sepals are also fused to form a bit of a tube - the calyx tube - around the tube made by the fused petals - the corolla tube. The flowers are arranged in whorls around the stems, some more densely packed than others and sometimes in spikes.
The ovary in these flowers is superior, so it's attached above the rest of the floral parts. It has four lobes with the style attached in the middle of these. These lobes ripen into little nutlets which fall out of the tube.
The stems of this family are very distinctive. They are square in cross-section, so when you look at them and feel them they will clearly have four angles or corners.
The leaves of plants in this family are arranged in opposite pairs, with pairs usually at right-angles to each other as they go up the stem. A lot of these species produce volatile oils in their tissues, giving them a strong scent when they are rubbed or crushed - this is what gives them their value as herbs.
So, if your plant has tubular flowers with an upper and lower lip, arranged in a whorl around the stem, and that stem is square, with leaves in opposite pairs, you are likely to be looking at a Lamiaceae, especially if it has a strong scent.
Look out for these three species when you are out and about:
• White dead-nettle (Lamium album)
• Selfheal (Prunella vulgaris)
• Yellow archangel (Lamiastrum galeobdolon)
[Note, botanical names should always be written in italics (or underlined if handwritten)]
