Miscellaneous Sapindaceae

 

The scope of the Family Sapindaceae does not yet appear to be fully settled and, despite the availability of DNA analysis etc, it is one in which the taxonomists still agree to differ. It occurs chiefly in the tropics and sub-tropics but a few genera extend into temperate climate provenances. It may or may not include Acer and Aesculus (depending on the opinions of the taxonomist and the genetic markers to which they attribute prominence) but it does appear to include the following genera, which contain species suitable for cultivation in temperate climates:- Alectryon, Dipteronia, Dodonea, Koelreuteria, Ungnadia and Xanthoceras.

 

The seeds of these genera are all of a sufficient size to be handled individually both at harvest and during the germination process. Generally the viability levels are high (<90%).

 

Alectryon

 

The genus Alectryon consists of about fifteen species of evergreen trees and shrubs which occur in the tropics and subtropics of South East Asia, the Philippines and Eastern Australasia. The Titoki (Alectryon excelsus) of New Zealand, however, is exceptional in that it occurs in temperate climatic areas. It develops into a spreading, evergreen tree - sometimes with a twisted trunk, and could reach nine or ten metres tall with tough, shiny green leaves.

 

The Titoki flowers in early summer with inconspicuous purplish flowers. The fruit is initially a green hairy capsule which takes a year to mature - when it becomes hard and woody; it then splits to allow a red, raspberry-like, fleshy aril type structure to emerge which contains the single black seed with a small pale coloured hilum scar.

 

The seeds remain on the tree for some time until they are taken by birds – so they can readily be picked by hand when convenient. The seeds are separated from the arils by fermentation. Fresh seed will then germinate without further treatment at 20˚C. Stored seed may develop a hardish seed coat condition which can usually be overcome by an extended warm water soak.

 

Dipteronia

 

The genus Dipteronia contains two species - D. sinensis and D. dyeriana and, superficially, appears very close to Acer. Both species are native to Central and South West China. The latter is regarded as rare and endangered.

 

They are generally large multi-stemmed shrubs but sometimes single stemmed trees. They are deciduous and have pinnate leaves. The racemes of inconspicuous flowers are produced during the spring. The flowers are structurally bisexual but are functionally male or female. In the autumn however the shrubs can be covered with large clusters of fruits which are initially green and mature to a distinctive red.

 

The individual fruit is a samara which consists of two nutlets which are compressed and are surrounded by two semicircular wings.

 

The seeds, once mature (ie having dried to the dispersal stage), have a hard seed coat which can usually be mitigated by an extended warm water soak. Once the seed is imbibed it exhibits an endogenous embryo dormancy - which requires a chill of 84 days at 3˚C to permit germination which then will occur in seven to ten days at 15˚C.

 

If it is possible to collect seed locally, then it would be advantageous to collect the samaras as they turn colour – ie before the seed coat hardens.

 

Dodonea

 

The ‘Hopbushes’ (Dodonea) are a genus consisting of about seventy species which have an extraordinarily extensive geographic distribution through the tropics and subtropics of Africa, Southern Asia, Australasia and the Americas – chiefly in the Southern Hemisphere and with about sixty of these species endemic to Australia. Several occur in Tasmania and therefore have a temperate provenance and are suitable for cultivation in such climates.

 

The inconspicuous flowers are wind pollinated and the species are either monoecious or dioecious; the flowers are produced in short racemes. The fruit is a colourful capsule with two or three wings which at maturity dries, hardens and bursts to expel the seeds. The seeds are usually black and develop a hard seed coat by dispersal.

 

The commonest species in cultivation is D. viscosa – which has a huge range through the subtropical/warm temperate climates of the whole distribution of the genus – it therefore tends to be variable in habit – depending on its provenance. The three to four winged capsule turns purple red at maturity, becomes brittle and then breaks up liberating two to three black seeds which are 2-3mm in diameter. The seeds have a hard seed coat which, if treated when fresh can be mitigated by a warm water soak which starts with pouring boiling water over the sample (4 to 5 volumes). If the seed has been stored it may need scarification to degrade the seed coat and permit imbibition. Germination will be prolific at 20+˚C.

 

Koelreuteria

 

The genus Koelreuteria consists of three species of medium sized, deciduous trees from South and East Asia. They are characterised by their pinnate leaves and large panicles of small, but showy, yellow flowers in late summer.

 

Koelreuteria paniculata - the so-called Golden Rain Tree of China is the hardiest - although in the south of the country K. bipinnata is sometimes seen.

 

Fruit is sometimes produced in the UK but it requires a warmer and brighter late summer than is the norm to achieve this and develop a viable crop of seeds. The fruit itself is a trilocular, bladder-like pod which turns from green to beige and then to red/pink. In a good year they are produced in profusion. The seed is easily extracted by collecting the pods just before they split open and then gently drying in a paper bag – The fruit splits down the median sutures to liberate the seeds – which are produced one per locule.

 

The seeds are brown at dispersal and mature to black (about 7.0K seeds per Kg). They have a pale hilum and are like small Aesculus seeds. When mature they can be successfully stored dry for a couple of years.  Unless the seed is treated immediately it is shed it is likely to have developed a reasonably hard seed coat - in the early stages this can be overcome by a warm water soak  but later will require a mild scarification to permit imbibition. The seeds also have an endogenous embryo dormancy which will require a 63 day chill at 3˚C to mitigate.

 

Ungnadia

 

The Mexican Buckeye (Ungnadia speciosa) is a monotypic genus - this Buckeye is native to North East Mexico and adjacent Texas. It is a very decorative shrub or small tree and will tolerate arid summer conditions. It can be cultivated in the drier, milder niches of the UK.

 

It produces its attractive crowded clusters of purple-pink, 2-3cm diameter, five-petalled flowers just before bud break, on the otherwise bare branches.

 

The fruit is a trilocular capsule - which when mature is about 5cm across, smooth, light brown and splits on the median suture of each locule to liberate the seeds. Often the capsules will persist until spring. The seeds are like small Aesculus seeds, globular – 2cm in diameter (about 750 per Kg), dark brown-black and develop one per locule.

 

The fresh seeds will usually germinate without constraint - provided that the temperature is warm enough (20˚C+). It would be prudent to give them a warm water soak before attempting germination. If the seeds have dried then scarification to abrade the seed coat slightly before the warm water soak is advisable.

 

Xanthoceras

 

The monotypic genus (Xanthoceras sorbifolium) is the only remaining survivor of the early stages of evolution in the Sapindaceae. It emanates from Northern China where it develops as a spectacular, deciduous, large shrub to small tree. It is hardy in all but the coldest areas although late spring frosts can be a problem for the emerging vegetative buds.

 

The plant produces light green, pinnate leaves and erect, tall (20 to 30 cm) panicles (like a Horse Chestnut candle) of five petalled white flowers, each 2 to 3cm in diameter, with a maroon centre – these are produced at or just before bud break.

 

The fruits are round, trilocular capsules, 5 to 6cm in diameter, leathery, green (quickly maturing to light brown) and smooth-skinned like a small Aesculus x carnea capsule. This will split, from the apex, into three sections along the median sutures of each locule to liberate the seeds. Each capsule could potentially produce 16 to 18 seeds but 10 to 12 is the norm. The fruits can be collected quite successfully at this stage and allowed to open by gentle drying in a paper bag.

 

The round, Aesculus-like seeds are 1.5cm in diameter and are sometimes flattened on one side. They generally exhibit a very high level of viability (90 to 100%) when fresh. When fresh they are light brown in colour and as they age the colour deepens to dark tan. Stored seed often develops a hard seed coat which requires low level scarification to allow for water uptake and imbibition, although a prolonged warm water soak may achieve the same result. The imbibed seed will respond to a chill of 63 days at 3˚C - this will certainly speed and synchronise germination at 18 to 20˚C.