CROATIAN FLORA - Sweet Chestnut

Sweet Chestnut Castanea sativa Mill., Fagaceae Family Sweet chestnut is a deciduous tree with a thick tree top that typically reaches the height of 20 to 35 meters. The bark of young branches and shoots is smooth, green or red-brown with many light lenticels (small openings that look like freckles or notches). With time, it turns dark grey-brown with deep longitudinal grooves. The leaf is elongated and spear-like with a pointy tip and a jagged edge. It is 12 to 20 cm long and 3 to 6 cm wide, dark on the top side and lighter on the bottom side with pronounced veins, shiny and slightly leathery. Its flowers are small, unappealing and of a single sex: the male yellow-white flowers with numerous anthers are gathered in groups of three or more and form pointy upright catkins 10 to 30 cm long. 3-4 greenish female flowers are located at the base of each male blossom. Chestnut usually blossoms during the month of June. The fruit is round or a flattened walnut of a shiny red-brown colour. Typically, two or three can be found in a common prickly cupule or an involucre that, when it ripens, closes on the top side with four valves. The fruit ripens in October, and an individual tree can produce as much as 200 kg of fruit! Sweet chestnut is the only European member of the chestnut genus that has a total of 9 genus, and it is considered a glacial relict – the genus has survived glaciation as it moved south away from the cold. It is believed that the sweet chestnut has survived the ice age in Anatolia and the Caucasus. Once the ice retreated, it spread to the Mediterranean countries and central Europe with the assistance of the humans during the ancient times. Nowadays, it naturally grows in forests from the Caspian Sea to the Atlantic Ocean as it prefers acidic soil and mild and rainy climates, and is grown around the world. In Croatia, sweet chestnut grows in woods in the mountain area belt, that is, on the mountains of the central and north-west Croatia, as well as Istria. People were growing sweet chestnut as far back as 2500 BC. It was mostly planted and spread around Europe by the ancient Romans due to its precious fruit. The fruit of sweet chestnut is very nutritious because it contains up to 45 % starch so it can be used to produce flour. It is rich with vitamins A, B and C, minerals such as phosphorous and potassium, as well as folic acid. It is consumed either cooked or roasted, or is used to prepare various dishes and sweets. Folk medicine uses it to alleviate liver ailments and it has an anti-inflammatory effect so it is recommended for persons who suffer from arthritis and rheumatism. In addition to its fruit, its wood is also very useful as it is very resistant to rotting due to large amounts of tannin. Chestnut wood is used across Europe to make poles for vineyards, stakes, roof beams and barrels. Chestnut trees have a long lifespan so there are many century-old trees. A tree in Italy is considered to be the oldest as some believe that is more than 3000 years old! Unfortunately, during the middle of the last century, European forests have been threatened by a type of a fungus that causes bark cancer and trees to die, and it has extended to the Croatian forests as well. In Croatia, cultivars of the sweet chestnut grown for its large fruit are known as “maruni“ or “maroni“. The trees in Istria are especially revered as indicated by the logo of the Učka Nature Park - a chestnut fruit. Sweet chestnut is also a true or edible chestnut of the Castanea genus and should not be confused with the inedible fruits of the trees from the distant Aesculus genus – that is called “wild chestnut“ due to its somewhat similar prickly fruit. Vanja Stamenković, Ph.D., Expert Consultant, Botanical Gardens, Faculty of Mathematics, University of Zagreb