''Juglans sigillata'',

common name In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often con ...

iron walnut (, pao he tao), is a species of tree in the walnut family

Juglandaceae The Juglandaceae are a plant family known as the walnut family. They are trees, or sometimes shrubs, in the order Fagales. Members of this family are native to the Americas, Eurasia, and Southeast Asia. The nine or ten genera in the family have ...

native to the eastern

Himalayas The Himalayas, or Himalaya ( ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the Earth's highest peaks, including the highest, Mount Everest. More than list of h ...

and western China. The tree has been cultivated for its edible

walnut A walnut is the edible seed of any tree of the genus '' Juglans'' (family Juglandaceae), particularly the Persian or English walnut, '' Juglans regia''. They are accessory fruit because the outer covering of the fruit is technically an i ...

s, and there have been at least 80 authorised or approved

cultivar A cultivar is a kind of Horticulture, cultivated plant that people have selected for desired phenotypic trait, traits and which retains those traits when Plant propagation, propagated. Methods used to propagate cultivars include division, root a ...

s produced after successful implementation of grafting technology.

Description

Iron walnut is a medium-sized deciduous tree reaching heights up to . The

leaves A leaf (: leaves) is a principal appendage of the stem of a vascular plant, usually borne laterally above ground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, stem, ...

are long, alternate, compound, with leaflets, each long and . 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

"iron walnut" derives).

Taxonomy

Iron walnut was long known in China before it was

formally described A species description is a formal scientific description of a newly encountered species, typically articulated through a scientific publication. Its purpose is to provide a clear description of a new species of organism and explain how it differ ...

in 1906 and given the scientific name ''Juglans sigillata'' by French

botanist Botany, also called plant science, is the branch of natural science and biology studying plants, especially Plant anatomy, their anatomy, Plant taxonomy, taxonomy, and Plant ecology, ecology. A botanist or plant scientist is a scientist who s ...

. Subsequently, it was largely neglected in western scientific literature until studied by the Chinese botanists and in the ''

Flora of China The flora of China consists of a diverse range of plant species including over 39,000 vascular plants, 27,000 species of fungi and 3000 species of bryophytes.Wu, Z. Y., P. H. Raven & D. Y. Hong, eds. 2006. Flora of China. Vol. 22 (Poaceae). Sci ...

'' series in 1979.

Uses

The tree has been cultivated for its edible nuts, and there have been at least 80 authorised or approved

s produced after successful implementation of grafting technology. It is widely cultivated in China for

production and wood. It is commonly found in

Yunnan Yunnan; is an inland Provinces of China, province in Southwestern China. The province spans approximately and has a population of 47.2 million (as of 2020). The capital of the province is Kunming. The province borders the Chinese provinces ...

, China's top walnut producing region in terms of acreage and yield, but also is found in

Guizhou ) , image_skyline = , image_caption = , image_map = Guizhou in China (+all claims hatched).svg , mapsize = 275px , map_alt = Map showing the location of Guizhou Province , map_caption = Map s ...

Sichuan Sichuan is a province in Southwestern China, occupying the Sichuan Basin and Tibetan Plateau—between the Jinsha River to the west, the Daba Mountains to the north, and the Yunnan–Guizhou Plateau to the south. Its capital city is Cheng ...

and

Tibet Tibet (; ''Böd''; ), or Greater Tibet, is a region in the western part of East Asia, covering much of the Tibetan Plateau and spanning about . It is the homeland of the Tibetan people. Also resident on the plateau are other ethnic groups s ...

in China. It is sometimes grown in gardens and parks as an

ornamental plant Ornamental plants or ''garden plants'' are plants that are primarily grown for their beauty but also for qualities such as scent or how they shape physical space. Many flowering plants and garden varieties tend to be specially bred cultivars th ...

. Outside of its native range, it was first cultivated at

Hackfalls Arboretum Hackfalls Arboretum is an arboretum in New Zealand. It was founded in the 1950s by Bob Berry (dendrologist), Bob Berry. It is part of Hackfalls Station, a sheep and cattle farm of about 10 square kilometres, owned by the Berry family. The farm is ...

in New Zealand in about 2000, and then more widely from 2005. ''J. sigillata'' is closely related to the Persian walnut ''

Juglans regia ''Juglans regia'', known by various common names including the common walnut, English walnut, or Persian walnut amongst other names, is a species of walnut. It is native to Eurasia in at least southwest and central Asia and southeast Europe, ...

''. 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 ''

'' 49 million years ago.

References

sigillata {{Fagales-stub