iron walnut

Iron walnut is a medium-sized deciduous tree reaching heights up to 25 metres. The leaves are 15–50 centimetres long, alternate, compound, with 9–11(–15) leaflets, each 6–18 cm long and 3–8 cm wide. The leaflets have entire or minutely serrated margins. The nuts are globose to oval, with a pointed apex and bumps and seal-like depressions (sigillatae, from which the scientific name derives) in the very thick, hard shell (from which the common name "iron walnut" derives).

The tree has been cultivated for its edible nuts, and there have been at least 80 authorised or approved cultivars produced after successful implementation of grafting technology. It is widely cultivated in China for walnut production and wood. It is commonly found in Yunnan, China's top walnut producing region in terms of acreage and yield, but also is found in Guizhou, Sichuan and Tibet in China. It is sometimes grown in gardens and parks as an ornamental plant. Outside of its native range, it was first cultivated at Hackfalls Arboretum in New Zealand in about 2000, and then more widely from 2005. J. sigillata is closely related to the Persian walnut Juglans regia. A 536.50-Mb genome has been sequenced to provide a solid foundation for additional genomic studies in nut crops and related species, as well providing valuable resources for plant breeders. Demonstrating an estimated divergence time between J. sigillata and the more widely cultivated Juglans regia 49 million years ago.

== References ==