Rare Tree of Heaven cousins (Ailanthus sp. div.)

The Common Tree of Heaven (Ailanthus altissima/glandulosa) it is medium size expansive tree which is forbidden to growing in numerous areas, for example in Poland. It can become a noxious weed. But there exists numerous other species in genus Alianthus (there are total 10 species in this taxon) which are allowed to growing. Some of them are tropical, but other are enough frost hardy to survive in northern temperate areas. I grew 2 such species. They are very rarely planted (hard to finding) and have been planted in Polish botanical gardens only 1-2 times in history. They are: Downy Tree of Heaven (Ailanthus vilmoriniana) and Girald’s Tree of Heaven (A. giraldii). They both are similar to A. altissima but they are different in some details.

 

The young spring shoot of Girald's Tree of Heaven (Ailanthus giraldii)

I propagated them by seeds (sown without any pretreatment in pots inside in spring). They are extremely fast growing and can attain to about 8-9m (= 30ft) within 10 years. They are starting to flowering within 8-10 years from seeds. They are dioecious. The flowers are inconspicuous but created in large panicles. The trees can be cutted back one time in year with allowing only one shoot which can attains a few meters tallness and creates very large leaves (it gives very unusual, tropical look). 

The huge pinnately-compound leaf of young tree (about 1,8m = 6ft long)

 Downy Tree of Heaven (Ailanthus vilmoriniana) differs from other species only by soft spines which cover young shoots and more teeth on leaflets (2-4 at each side of leaflet). In other features is very similar to A. altissima and was also regarded as only variety of it (Ailanthus glandulosa var. spinosa). It is hardly frost hardy in my zone 6b and in severe winters the trunk can break due to frost. Young trees should be mulched but later they are enough frost resistant. 

The seedling in second year of life

Young spring shoots are very colorful

The young stems are covered by soft spines

There are 2-4(5) teeth on each side of the leaflets (more than on Common Tree of Heaven)

The spines are red if exposed to sun or green of grew in shade

The spnes are ended by small round red glands

Older spring shoots

A few years old tree

The bark

The plant in flowers (male)

The cutted trunk

Girald’s Tree of Heaven (Ailanthus giraldii) creates very large leaves (to 1,8m = 6ft on young trees) and large samaras (fruits) about 4,5-6 x 1,5-2cm (= 1,8-2,4 x 0,6-0,8inch). It is more frost resistant than pervious species, but in severe winters end of shoots are killed by frost. 

Young spring shoots are very ornamental

The trunk of young tree

The tree about 5 years old

First flowers was created after about 8 years from seeds

The female flowers

Young fruits

The tree in winter

The trunk of mature tree

The cutted trunk (the wood of this species in prized to making fornitures)

The fruits of this species are quite large (larger than ones of Common Tree of Heaven)

Both these species can easily hybridize. I harvested hybrid seeds. I had one male tree of A. vilmoriniana and one female A. giraldii. Recently I cutted them (they were dangerous to small house in my garden – they grew too close up it and their roots could damage a basement of this building) but I still have seeds and suckers from roots. I am going to plant them in other safe place. They could be again large soon.