C. sativa attains a height of 20–35 metres (66–115 feet) with a trunk often 2 m (7 ft) in diameter. Around 20 trees are recorded with diameters over 4 m (13 ft) including one 7.5 m (25 ft) in diameter at breast height. A famous ancient tree known as the Hundred Horse Chestnut in Sicily was historically recorded at 18 m (59 ft) in diameter (although it has split into multiple trunks above ground).[3] The bark often has a net-shaped (retiform) pattern with deep furrows or fissures running spirally in both directions up the trunk. The trunk is mostly straight with branching starting at low heights. The oblong-lanceolate, boldly toothed leaves are 16–28 centimetres (6–11 inches) long and 5–9 cm (2–4 in) broad.
The flowers of both sexes are borne in 10–20 cm (4–8 in) long, upright catkins, the male flowers in the upper part and female flowers in the lower part. In the Northern Hemisphere, they appear in late June to July, and by autumn, the female flowers develop into spiny cupules containing 3–7 brownish nuts that are shed during October. The female flowers eventually form a spiky sheath that deters predators from the seed.[4] The sweet chestnut is naturally self incompatible, meaning that the plant cannot pollinate itself, making cross-pollination necessary.[5] Some cultivars only produce one large seed per cupule, while others produce up to three seeds.[5] The nut itself is composed of two skins: an external, shiny brown part, and an internal skin adhering to the fruit. Inside, there is an edible, creamy-white part developed from the cotyledons.[5]
Sweet chestnut trees live to an age of 500 to 600 years.[6] In cultivation they may even grow as old as 1,000 years or more.[5]
