Orchidaceae

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. Plants are classified into families based on characteristics that they share; so, the way to identify a plant’s family is to know these characteristic features.

Today we’re going to look at the Orchidaceae, or orchid family. This is one of the biggest of the plant families, with around 26,000 species, plus many human-made hybrids. The Orchidaceae are found worldwide, apart from (as usual) Antarctica, and there’s an especially high diversity in tropical areas. Orchids are perennial herbaceous plants. They grow on the ground or as epiphytes in trees; a few are vines, namely Vanilla species, the vanilla orchids.

The main uses of orchids are as ornamental plants, example species and hybrids of Dendrobium, Vanda, Cymbidium and Phalaenopsis (moth orchids). Vanilla planifolia is grown as a spice for flavouring. A number of species don’t possess chlorophyll like most plants, giving them a pale appearance. These rely on fungi for sustenance.

There are roughly 55 species in the UK and several of them hybridise with each other. The UK species all terrestrial, growing on the ground. Dactylorrhiza fuchsii (common spotted orchid), Epipactis helleborine (broad-leaved helleborine), Neottia nidus-avis (bird’s-nest orchid), Spiranthes spiralis (Autumn ladies’-tresses), Neottia cordata (lesser twayblade) and Orchis mascula (early purple orchid) are but a few examples.

The flowers of orchids are very distinctive. They are irregular in symmetry. They have three sepals, which are usually coloured like the three petals. The petals and sepals generally look similar to each other, apart from the lowermost, centre petal. This petal forms a lip, called the labellum. The labellum varies in shape between species and genera, from lobed in Dactylorrhiza to insect-shaped in Ophyrys apifera (bee orchid), to elongated in Platanthera bifolia (lesser butterfly orchid) and pouch-like in Epipactis helleborine. The labellum often has markings on it or different colours to the rest of the petals and sepals. In many species it also forms a spur at the back of the flower. Flower colour is often pink, purple or white, or a combination of these. Fun fact: in the bud the labellum is at the top of the flower but as the flower matures it twists 180 degrees. So, orchid flowers are actually upside-down. Go figure.

Instead of the standard stamens and stigma, orchid flowers have a structure called a column which holds the reproductive parts. Pollen is held in two distinct masses called pollinia instead of as loose grains. There are two fertile stigmas at the base of the column and a third, infertile one that is modified into a piece of tissue called the rostellum that sits between the pollinia and stigmas. The flowers are mostly insect-pollinated, with the pollinia sticking to the bodies of visiting insects, to be carried away to another plant, though some specie scan also self-pollinate. The ovary is inferior.

The fruits of orchids are capsules containing vast amounts of very tiny seed which is dispersed on the wind.

The leaves of Orchidaceae are simple and entire, mostly arranged alternately on the stems, with a few species, like Neottia ovata, having opposite leaves. The leaves are often compressed into a rosette. The leaves on the flowering stems may be scale-like and reduced. The leaves have parallel veins and tend to be thick. Some species have spotted patterns on their leaves.

So, if your plant has irregular flowers with three petals and three sepals, and the bottom petal is modified into a labellum, the fruit is a capsule and the leaves are arranged alternately on the stems, or in a rosette, then you have yourself an orchid.

See if you can find any of these species on your travels:
• Dactylorrhiza fuchsii (common spotted orchid), with a dense spike of pink flowers with patterned labellae and spotted leaves
• Epipactis helleborine (broad-leaved helleborine), with green and sometimes reddish flowers with pouch-like labellae, and green leaves
• Neottia ovata (common twayblade), with yellowish-green flowers with two-pronged labellae, and a pair of opposite leaves