Celastraceae

 

This extensive Family of some ninety to one hundred genera and containing about thirteen hundred species of shrubs, trees and climbers chiefly occurs in the tropics and sub-tropics.

 

Only three genera contain species with a relevant temperate distribution - Celastrus, Euonymus and Maytenus.

 

All of these three genera have brightly coloured, valved, fruit capsules which, when ripe, split open to display the red aril type seeds which still adhere to the fruit case; these are normally taken by birds. Thus it is relatively easy to collect the fruits just as they are about to split (or have split) and then dry them sufficiently that the seeds can be separated from the capsules. It is not advisable to collect the fruits prior to this stage as artificial drying does not cause the capsules to dehisce and extraction is then manual and tedious.

 

Celastrus

 

The genus Celastrus contains thirty to forty species of shrubs and climbers which have mainly a tropical and sub-tropical distribution but with a few outliers in temperate climates. Only three or four species are suitable for cultivation in the UK. The plants are dioecious with greenish yellow inconspicuous flowers which are followed, in the autumn, by a two to four valved, dehiscent capsule which is normally orange to yellow.

 

Each fruit cell contains up to two seeds which are red fleshy arils. The seeds can be separated from the flesh (which may contain a germination inhibitor) by drying the seeds and agitating them roughly to separate the flesh or by maceration and fermentation. If fresh seed is used and separated by the wet method it is unlikely that the seed coat hardens sufficiently to prevent water uptake. If it is suspected that the seed coat has hardened then an organic acid treatment will reduce the seed coat.

 

These temperate provenance species exhibit an endogenous dormancy control which is mitigated by chilling the imbibed seed at 3˚C for 63 days. Germination will then occur satisfactorily at 20+˚C.

 

The following species from temperate provenances, which are all twining or scandent climbers, are found in cultivation in the UK - C. hypoleucus, C. orbiculatus, C. paniculatus, C. rosthornianus, C. rugosus and C. scandens.

 

 

Deciduous Euonymus

 

Euonymus is a large genus of some 160 to 170 species. The species are chiefly found in the Northern Hemisphere. There are both deciduous and evergreen species which barely look as though they are related - however the fruits and flowers easily distinguish their relationship. The deciduous Euonymus europaeus is native to the UK and adjacent Europe – its English name Spindle Bush (or Tree) indicates its traditional use as a preferred wood for making spindles for the textile industry.

 

The deciduous species of Euonymus are chiefly distributed in temperate climates and virtually all the cultivated species are grown for their decorative, colourful fruits and often brilliant and intense autumn foliage tints - as well as being tolerant of ‘chalky’ soils. The flowers, which are produced during the summer, are usually small, insignificant and dull. They are normally greenish yellow in colour.

 

These deciduous species are normally propagated from seed although the particular variants are usually propagated from cuttings. It is prudent to grow several stock plants (not of the same clone), so that cross pollination occurs - as sometimes isolated plants (which are necessarily self pollinating) leads to poor quality and low levels of seed production.

 

The fruits consist of a locular capsule which has four (or sometimes five) locules, each enclosing a single seed (if there has been a satisfactory pollination). The more or less globular seed usually has a distinct bright yellow or orange covering ‘skin’ and this is exposed in situ when the capsule opens. Each locule of the fruit has a median diagonal suture which, when ripe, splits and flattens backwards to expose the seeds. The capsule, when ripe, is usually brightly coloured - normally shades of pink or red. The seeds are taken and dispersed by birds but some species, in their natural domain, are eaten by deer, other ruminants and bears. Internally the seed has a hard protective seed coat which is a protection against digestion in the gut. In the UK the majority of these species ripen the fruits from mid-October onwards and the seeds should be collected before the birds remove them. It is not suitable to collect the fruits, at an early stage, before the sutures open as the capsules are strong and are tedious to split open; however if the capsules are collected just as the very first suture on the plant is splitting then they can be harvested and gently dried for 24 hours - when they will split and open readily and after a further day of drying the seeds will separate easily.

 

Each seed consists of a conventional embryonic core which is protected by the hard seedcoat, outside this is a thin but nutritious, fatty (white) layer enclosed in the brightly coloured skin - which is the attractive advertisement agency for dispersal. The seeds remain stuck to the fruit, for some time, from where they are taken by the predator.

 

The seeds are prepared for propagation initially by separating them from the capsule and then removing the external skin and flesh – this is achieved by macerating and then fermenting in warm water for a few days – the seeds will sink to the bottom of the container and the dross can be decanted off. The seeds should then be rigorously washed using a small amount of detergent and then rinsed - this ensures that all the fatty flesh has been removed and is not a potential barrier to imbibition. The next stage is to reduce the ‘hard’ seed coat to a level at which it becomes water permeable. This can be achieved either by a few weeks of warm stratification with or without an accelerator. Alternatively it may be achieved by an organic acid digestion using a 1% (10,000ppm) solution of citric acid – the seeds are soaked in the acid for +/-96 hours in warm environmental conditions – which should be a sufficient period to degrade the seed coat.

 

Once the seeds have imbibed they require a period of chilling to mitigate an endogenous dormancy condition. It would appear that a period of 63 days at below 3˚C will be sufficient. Germination can then be achieved with a speedy and synchronised emergence at temperatures in excess of 15˚C.

 

It is possible that an early collection of the fruits before the seed coat hardens will avoid the problem and allow for immediate imbibition but the extraction of the seed from the capsules is difficult and thus essentially impractical.

 

The following species will all respond to the treatment indicated above-

Euonymus alatus,  E. bungeanus,    E. europaeus,

E. grandiflorus,   E. latifolius,   E. maackii,

E. oxyphyllus,    E. phellomanus,  E. planipes,

E. sachelinensis, E. sargentianus and E. yedoensis.

 

Maytenus

 

This genus of evergreen and semi-evergreen trees and shrubs contains over 100 species which principally have a tropical and subtropical distribution throughout the world. There are two species, however from the southerly parts of Chile and Argentina which have a temperate provenance - M. boaria (which is marginally hardy) and M. magellanica (which is cold hardy).

 

The inconspicuous yellow flowers are produced in profusion in early summer and are hermaphrodite (or sometimes monoecious). On an established plant flower and fruit production is prolific.

 

The fruit is a two valved capsule which splits in the autumn to display the one or two seeds, these remain attached for some time and are taken by birds. The capsule is bright yellow in M. magellanica and dull green in M. boaria. The seed is enclosed by a red skin containing an oily/fatty material and inside this is the seed which usually has a rugose seed coat.

 

The detail for seed extraction is the same as for Euonymus.

 

Although the seeds are usually taken by birds the seed coat does not seem to harden sufficiently to prevent imbibition.

 

Germination at 20+˚C is normally prolific.