Plant of the week – 13th July 2020 – Digitalis purpurea (foxglove)

Digitalis purpurea – the foxglove – in flower is an unmistakable plant, with its tall spikes of magenta flowers rising from the green of woodland floors and the brown of heathy hillsides in summer.

D. purpurea belongs in the Plantaginaceae family and is the only member of its genus native to the British Isles. It is a biennial (occasionally short-lived perennial) plant, forming a rosette of large, oval-lanceolate leaves in its first year. These leaves have rounded teeth on the margins and are downy all over, as is the stem.

In its second year, the stem elongates into a straight flower spike, up to a metre-and-a-half or so tall, from June to September. Sometimes there may be more than one spike.

The flowers of foxglove are typically a pink-purple colour, tubular, with dark spots on the lower lip that are outlined in white. However, it is not uncommon to see forms of foxgloves with white flowers, or paler pink. They are large, the corolla to 5cm long, and have a calyx (sepals) that are separate at the top and fused into a tube further towards the flower stalk. They hang to one side of the spike.

The flowers open from the bottom of the spike upwards, the lower ones opening while the upper ones are still developing. The species is also protandrous – the male parts of the flower mature before the female parts – which is an interesting cross-pollination mechanism. This means that the older flowers towards the bottom have receptive stigmas while the younger, upper ones are releasing pollen.

The main pollinators of foxgloves are bumblebees, which tend to forage from the bottom of the spikes upwards. When the bees visit a flower spike, they deposit pollen onto the receptive stigmas and collect more from the stamens before leaving to find another spike.

The fertilised flowers develop into capsules that produce large quantities of seeds, and the plants self-seed freely, germinating in great numbers after disturbance.

This plant generally prefers more acidic soils, though it will grow in a wide range of soil conditions and habitats, and is commonly seen across heaths and hillsides, in sunnier spots in woodlands, rocky outcrops in upland areas, verges and path-sides. It is also commonly grown as a garden plant, and this has led to its escape and naturalisation in countries outside its native range of Europe.

All parts of Digitalis purpurea are poisonous, with ingestion causing symptoms ranging from nausea and headaches to heart malfunction. Extracts from this species and its relative D. lanata are used to create a heart stimulant drug from the compounds digoxin and digitoxin found in their tissues.

Text and photos © Heather Forbes

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