Wednesday, April 14, 2010

Xanthoceras sorbifolium - Yellowhorn

Also called the "White Raintree". Xanthoceras sorbifolium which is native to northern China, is the only species in the Xanthoceras genus ( tribe ) of plants. Typically a vigorous large shrub or small, dome shaped tree to 15 feet; some records include: fastest recorded growth rate - 2 feet; 20 years - 30 x 30 feet; largest on record - 40 x 40 feet.
The pinnate, deciduous leaves are clustered near the tips of the branches and are up to 12 inches in length. The 9 to 17, sharply toothed, narrow elliptic leaflets are up to 2.5 inches in length. The smooth foliage is glossy, deep green above, bright green beneath.The foliage remains green late into the fall.
The fragrant flower up to 1.5 inches wide are 5 petalled and white with a deep red blotch near the base. They are borne in upright clusters up to 10 inches in length and the ends of old shoots in mid spring as the foliage emerges. This plant may bloom as young as 2 years of age.
They are followed by a smooth, thick-walled, rounded green capsule up to 2.5 inches in width that resembles a Walnut. Several pea sized seeds are contained within.
There is some genetic variability with this plant despite having no named cultivars.
Some plants have marble sized nuts that taste like Macadamia nuts if roasted.
The gray-brown bark is fissured into scaly ridges.
Hardy zones 3 to 7 in full to partial sun on fertile well drained soil. It is tolerant of alkaline soil as well as extremely cold winters but needs a long hot summer to flower and fruit well.
In cool summer climates such as England; it can be planted along a warm sunny south facing wall. It hates growing in containers and should be planted while small since older Yellowhorns aren't fond of transplanting.
Propagation is from seed and also cuttings and suckers. Root cuttings taken in winter are also an option. The seed does not require pre-treatment however does germinate faster with a 3 month cold stratification at 41 F.

* photo taken on April 11 2010 @ U.S. National Arboretum

* photos taken on May 16 2010 @ Cylburn Arboretum, Baltimore, MD

* photos taken on August 3 2010 @ University of Guelph Arboretum, Ontario

* photo taken on July 26 2015 @ Niagara Parks Bot. Gardens, Niagara Falls, ON

* historic archive photo

'Clear Creek'
Considered exceptionally hardy but otherwise identical to the species. It was developed by Green Acres Nursery in Colorado.

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