Eleagnaceae

 

This small Family which contains only three genera of shrubs and small trees – Eleagnus, Hippophae and Shepherdia - is native mainly to the Northern Hemisphere through temperate and sub-tropical climates but it also diverges through tropical southern Asia to North East Australia.

 

The great majority of the species are native to xerophytic conditions – sea shores, semi-deserts etc (and indeed some have adapted to halophytic conditions). They tend to be successful in competition, on such depauperate soils, because of their ability to engage in a symbiotic relationship with the actinorrhizal bacterium Frankia. Thus they are useful soil ameliorants or can become invasive weeds – depending on the scenario! This competitive ability is also enhanced by their habit of prolific seed production. In many cases they succeed perfectly well as ornamental plants in conventional soil types.

 

The majority of species are thorny and the leaves and shoots are often covered with scales or hairs – a condition often associated with the need for the plant to conserve water. The fruits are generally fleshy, colourful, edible and highly nutritious and are eaten by a range of animals and birds; hence, in general, the seeds have hard, resistant seed coats (usually the endocarp) to protect the seeds in their passage through the gut – although not always impermeable to water.

 

Eleagnus

 

This genus of ‘the Oleaster and the Silverberries’ contains between fifty and seventy species of deciduous or evergreen shrubs and small trees. It is distributed through temperate and sub-tropical Asia and then via the Philippines to North East Australia and with one species in North America. There are only a relatively few species (probably about ten) which are relevant for cultivation in temperate climates.

 

The stems and leaves are covered in scales and/or hairs which produce a silvery cast to the overall impression of the plant.

 

The fragrant flowers are generally insignificant and are produced in late spring. These give rise, in September – October, to a prolific crop of persistent, fleshy drupes, with edible flesh, which contain one, dry, dehiscent achene.

 

The fruits are collected by hand – but with care as the fruiting branches can be thorny. The seeds are extracted by maceration of the fruits and then decanting off the pulp and dross. The seeds can then be washed and cleaned fully. Although hard seededness is not a particular problem it would be prudent to process the seeds into treatment without drying.

 

Generally the seed coat (endocarp) is not particularly hard and imbibition will occur, with fresh seed, as a result of a twenty four hour warm water soak. However if the seed has been dried and possibly stored it would be beneficial to mechanically scarify the sample prior to soaking.

 

The imbibed seeds are dormant and will respond to a period of chilling of 84 days at 3˚C. This physiological control however is not present in the embryo - as excised embryos will germinate in ten days at 20˚C – suggesting that the inhibiting agency was in the testa and/or the endocarp. Germination is most satisfactory at 20˚C.

 

Hippophae

 

The sea buckthorns are a genus of seven species, principally, from warm temperate towards very warm dry climates. The only species which are relevant for cultivation in temperate climates are the native H. rhamnoides and the Himalayan, H. salicifolia.

 

H. rhamnoides has a distribution from the Atlantic coasts of Western Europe right across the Northern Hemisphere to North West China and, over this range, is divided into eight sub species. In Western Europe it is generally confined to coastal areas inland as far as the salt spray reaches, as it will tolerate salty conditions. In Central Asia it is a plant of semi-deserts. It is native to and widespread in the UK where it is found above the shore line, in the range of salt spray, in such situations its root suckering habit makes it very suitable for stabilising sandy and dune areas.

 

In habit it will grow to three or four metres with a dense, stiff structure of very thorny braches; with narrow, silvery green, lanceolate leaves up to 8cm long.

 

Once mature the plant flowers prolifically, annually. Each inflorescence consists of only one flower which has no petals and develops only one seed. The plants are dioecious.

 

The roundish, orange, fleshy berry-like fruits are 6-9mm in diameter – juicy, soft and nutritious; they are very high in vitamin C. The berries are prolifically developed in compact bunches along the stem. Nowadays they are grown extensively, throughout the range, as a plantation fruit crop – improved strains with larger fruits and a higher nutritional status have been developed.

 

The fruits are difficult to harvest as the fruit clusters are liberally interspersed with spines which makes picking intolerable. For seed collection for nursery purposes it is best to shake the braches, when the fruits are soft and ripe, to dislodge the fruit onto a sheet on the ground. Probably only about 25% of the available fruits will fall. The seeds should be harvested as soon they are ripe and processed without delay, as germinability appears to decline the longer the seed remains in the softening flesh. The seeds should be processed without further drying, in order to avoid the possibility of hard seededness developing.

 

The seeds are extracted by maceration in water so that the skin, pulp and detritus can be floated off.

 

Although the seed coat is not particularly impermeable to water it will take at least forty eight hours of warn water soak in order to fully imbibe the seed.

 

The seeds have an endogenous dormancy which requires a chill for 84 days at 3˚C to overcome. Germination occurs, optimally, at between at 20 and 25˚C and seedling emergence will take seven to ten days.

 

H. salicifolia is from high elevations in the Himalayas and the same comments apply as above. However the chilling period is for 35 days (although lower elevation provenances may well not require this). Germination occurs optimally at 25˚C.

 

Both species appear to benefit from shallow sowing (ie just covered) and the seedlings flourish best in full sun. These are plants that grow in full sun and dislikes shade.

 

Shepherdia

 

The Buffaloberries (Shepherdia) of the west and north of North America are a small genus of three species. They are shrubs to small trees inhabiting, generally, areas of dry and poor terrain. The branches are thorny and the leaves and stems are covered in small star-shaped scales which give the plants an overall silver sheen.

 

The plants are dioecious and the flowers are carried singly or in clusters in the spring. They are without petals and are yellow to yellow-green in colour.

 

The fruits mature in the late summer and are drupe-like - about 3-8mm in diameter and each contains one achene. They are red skinned and fleshy - which is bitter to the taste. The smooth achenes or nutlets can have hard seed coats (significantly so in S. canadensis).

 

The fruits are collected by shaking from the branches when ripe – as the plants are thorny and hand picking is hazardous.

 

The seeds are extracted by maceration in water so that the skins, flesh and detritus can be floated off and the seeds washed clean. As the seed coat can harden when dried it is prudent to process the seeds into pregermination treatments straight away.

 

The seed coats of S. argentea and S. rotundifolia can be effectively penetrated by an extended warm water soak (ie several days). The seed coats of S. canadensis, however, are harder and although the recommendation is to scarify with a short sulphuric acid soak; an aggressive and abrasive scarification can achieve the same result but with safer process. This is followed also by the warm water soak.

 

All the species require a chill to overcome a physiological dormancy - S. argentea for 84 days, S. canadensis for 49 days and S. rotundifolia for 63 days at 3˚C. S. canadensis especially will germinate (at least to radicle emergence) at this low temperature so it is wise to monitor the stratifying seed and to sow the seed lot once this stage is reached. Germination at 20˚C is optimal for the germination of all the species.