Hart's-tongue

During the Italian Renaissance this plant was very popular with ladies of the nobility, known as belladonnas. At this time shiny, dilated pupils were perceived as a mark of beauty. Ladies going to an evening ball would put a few drops of the juice from the glossy black berries into their eyes and did not mind the resulting impaired vision.

Their pupils dilated through the action of the substance atropine found in deadly nightshade. Today ophthalmologists make use of this effect when undertaking a full examination of the eye. The substance is extremely toxic and is present in all parts of the plant.

Can’t stand clean-ups

The hart’s-tongue fern is a medium sized, evergreen plant, bearing ripe spores in the summer. The frond (the leaf) is undivided, tongue-shaped with entire edges and is glossy light green in colour. Spores sit in ‘sori’ or ‘spore-mounts’ with a membrane and occur in two parallel rows on the underside of the leaf.

Ecology and habitat

Hart’s-tongue fern occurs from the Atlas region of Morocco across to the Caspian Sea, and also in Japan and North America. It can be found across much of the Netherlands in damp shadowy places such as on old walls, on the sides of ditches, basalt slopes, forests, under thickets and on dead wood. This fern needs damp places to develop from the spore stage into a seedling. It can’t tolerate heavy frosts so the mild climate in urban areas provides the hart’s-tongue fern with the greatest chance of survival. Following a series of only moderately cold winters the fern has been able to increase its range especially in Western part of the Netherlands. Being a nitrogen-loving plant, the hart’s-tongue fern is benefitting from the eutrophication of the environment.

Threats

The hart’s-tongue fern is not threatened but legally protected, from amongst other things being dug up, and is on the increase - possibly as a result of improved air quality following reduced atmospheric sulphur dioxide levels – particularly on old walls. Increased levels of decaying wood in forests are beneficial to ferns, whereas clean-up operations of old walls are disastrous. Good examples of the hart’s-tongue fern in the wild can be seen on the north-facing wall at the entrance to the ‘Groene Plantage’ (formerly the Hugo de Vriesgebouw), the mainstay of the Dutch Society of Botanic Gardens next to the Amsterdam Botanic Garden.