Berberidaceae

 

A Family with a global distribution - consisting of 500 to 600 species of trees, shrubs and herbaceous plants which are attributed to four genera (Berberis, Epimedium, Mahonia and Vancouveria) - of which Berberis is the largest and dominant component. Nandina has often been included here but currently, on the basis of DNA assessment, it is attributed to its own Family – Nandinaceae.

 

Berberis and Mahonia

 

Both of these, closely related woody plant genera have, regularly over the years, been ‘lumped’ (into the single genus Berberis) or separated (into the two genera). They have a circum-polar distribution in the Northern Hemisphere chiefly in colder temperate climates but some species, on the southern fringes are also found in warm temperate situations – especially in arid conditions. They are also found in the Southern Hemisphere in South America.

 

Those species described as Berberis number about 450; while those described as Mahonia number about 100 species. The main distinction is that Berberis have simple leaves while Mahonia has pinnate leaves. Both groups contain evergreen and deciduous species. Berberis develops thorns from modified leaves on the stem while Mahonia produces well armed leaves.

 

The Barberries (Berberis) are found throughout most of the world except Australia but with most variety in South America, Africa and Eastern Asia. Mahonias are found in Europe, North Africa, Asia and North America.

 

The fragrant, hermaphrodite flowers in both groups are yellow but can sometimes be orange. Generally the plants are winter or spring flowering.

 

The fruit is a pulpy, colourful berry – in shades of pink, red and orange in Berberis - usually averaging about 1.5 seeds per berry and blue-black in Mahonia, often with a pruinose bloom and averaging 3 seeds per berry.

 

As a group these plants show a remarkable diversity of seed development – the Family contains seeds with linear and spatulate embryos and in many species the embryo is, at seed maturity, immature. The embryo sits in an oily endosperm - which has implications for storage temperature.

 

The major issue for the seedling propagator when producing these two genera is the fact that the greater proportion of species will hybridise in some degree and the source of seed should be considered in terms of its genetic integrity. B. darwinii and B. gagnepainii, for example, are particularly promiscuous while B. dictiophylla, B. julianae, B. thunbergii and B. vulgaris are usually reliable – largely because there are usually no suitably related genera available for potential hybridisation.

 

The seeds can be readily extracted from the ripe berries by maceration and the removal of the detritus in running water. It is important to continue cleaning the sample until all the flesh is removed - as there is some evidence to suggest that germination inhibitors are present in the flesh – especially in species from arid provenances. It is probably this characteristic which gives rise to the recommendation that the seeds of some Mahonias will benefit from leaching in order to promote germination.

 

As a general protocol, for species with no reliably described pre-germination treatments the following sequence might well be adopted – these treatments would appear to cover most of the extremes and ensure germination, even if it is excessive for some.

 

a) use freshly extracted seeds without drying;

b) warm water soak for 24hrs (up to 72 hours for arid land species which often have a marginal ‘hard’ seed coat) in order to ensure a complete imbibition and any leaching residue requirement;

c) warm stratification at 18˚C for 30 days to mature the embryo;

d) chill at 3˚C for 84 days;

e) germinate at 20˚C.

 

Not all species appear to require a chill but those that will germinate without pre-treatment will emerge more quickly and uniformly if given a 28 day chill prior to germination.