Fagaceae

 

The Beech Family is a significant group (more than 900 species) of both evergreen and deciduous trees and shrubs. These are currently segregated into seven relevant genera – Castanea, Castanopsis, Chrysolepis, Fagus, Lithocarpus, Quercus and the (relatively recently separated) monotypic genus Notholithocarpus (from Lithocarpus), there are three other monotypic genera - Colombobalanus, Formanodendron and Trigonobalanus (all three are, by some authorities, aggregated into the one genus Trigonobalanus) which are not dealt with here as they occur in the sub-tropics and tropics. The genus Nothofagus was included here but recent DNA assessment has shown it to be distinct and is now attributed to its own Family – the Nothofagaceae

 

The family has a wide distribution across the Northern Hemisphere but crosses the equator in South East Asia – where most of the species in this family are found. This tropical and subtropical area is the centre of distribution - so that relatively few species are found with a northerly occurrence in temperate climates. However, of those which have evolved and migrated to succeed in these climates, many are dominant in their respective habitats – eg Fagus sylvatica, Castanea sativa and many Quercus species.

 

Flower production is monoecious – the flowers are catkin-like and are produced in the spring. They are wind pollinated. Fruit production and dispersal usually takes one season but is sometimes eighteen months after pollination.

 

The nut-like seeds are carried in a fruit which is basically cup-shaped but which can be a spiny husk, which encloses the seeds completely - as in Castanea and Chrysolepis or which may be reduced to a scaly cup - as in Lithocarpus and Quercus. Each fruit contains from one seed, as is the norm in Quercus, to as many as seven.

 

The seeds usually have a rounded base which fits into the base of the cup of the fruit, they have a dry and protective skin when mature and are cylindrical to conical, sometimes laterally flattened (when there is more than one seed in a fruit) in shape and coming to a point at the apex. The linear embryo is situated at the apex with the radicle in the apex and the plumule below. There is no endosperm and the food store of chiefly carbohydrates is in the cotyledons.

 

The chief problem with the collection and short term storage of the seeds is associated with water loss – viability declines rapidly with drying. The seeds should therefore be harvested as they are dispersed or picked just before dispersal and then cool stored under moisture conserving conditions. It is probably prudent to store the seeds in relatively small batches as large batches tend to heat up as a result of their ongoing metabolic activity.

 

The seeds generally are big enough to handle individually with some (especially the Chestnuts) being substantial in size. This facilitates sowing and allows them to be station sown. As has been indicated by the position of the embryo in the seed, the seeds can be readily sown with the correct polarity - so that seedling growth is not checked at emergence. Although it would seem logical to sow the seeds with the point underneath - so that the radicle emerges directly downwards this position seems to impair the quick emergence of the plumule and it is therefore best to sow the seeds on their sides sloping slightly downward towards the point so that both the radicle and the plumule emerge with equal success.

 

In general virtually the entire family requires mycorrhizal associations for an adequate and regular performance of the individual seedling.

 

The largest genus, with about six hundred of the species, is the Oaks (Quercus).

 

Quercus

 

The Oaks (Quercus) are a very large and diverse genus of, both deciduous and evergreen, trees and shrubs which encompass the size spectrum from small, low-growing plants at the tree-line (the evergreen Quercus vacciniifolia in the Sierra Nevada of California) to massive spreading subjects capable of living for several hundred years (the deciduous European Q. petraea and Californian Q. lobata). There are, currently, recognised about 600 species - which are distributed throughout virtually all climatic and geographic regions of the Northern Hemisphere (except the Arctic). Although probably more than half of the species are native to tropical and sub-tropical climates, there is still a comprehensive range of species, with ornamental potential, which are found in temperate climates and many of these are suitable for growing in the British Isles.

 

As might be anticipated with a genus that contains so many species there is considerable diversity within the various characteristics, not least within the development, structure and production of the seeds and subsequently in the conditions necessary for seed germination.

 

Although the Oaks appear to be a relatively simple arrangement of species the picture just below the surface, at least for the taxonomists, is more complex. There are many groups of species which can develop considerable levels of genetic introgression but still represent, morphologically, a particular species. This is not an easily understood situation and for the propagator is only of concern for the specialist producer. Seeds should therefore be collected from single species stands as far from genetic pollution as possible.

 

The Oaks are part of the Fagaceae which also includes other genera with species occurring in temperate climates (inter alia - Castanea, Chrysolepis, Fagus, Lithocarpus) and which are of ornamental value in the various climates of the British Isles. In the case of Oaks the generic characteristic is to develop a single, nut-like, seed (acorn) which is carried in a cup (cupule), which may be stalked or sessile and, in general, is borne in an upright position on the terminal branchlets.

 

The genus Quercus is, initially, divided into two sub-genera:– a) Quercus - the larger proportion of species which would be recognised as Oaks in temperate climates and b) Cyclobalanopsis – the ‘Ring-cupped’ Oaks of Eastern and South-eastern Asia (c150 species) which occur chiefly in sub-tropical and tropical evergreen laurel forests. This latter group are characterised by a different cup structure which is made up of concrescent rings of scales and having the acorns produced in tightly packed clusters.

 

The sub-genus Quercus is sufficiently large to have sufficient distinctive characters to be divided into four or five sections:-

a) The White Oaks (section Quercus) range across the Northern Hemisphere through Europe, North Africa, Asia and North America. They have acorns which mature in six months and taste sweet or slightly bitter; the acorn cup is smooth and hairless on the inside and the lobes of the leaves are more or less rounded and have no bristle points. The flowers have short styles. Virtually all the species here will hybridise with each other so that collecting seeds other than from dense single species stands will produce seedlings of doubtful authenticity. The two native Oak species in the British Isles will potentially hybridise with any of this group so that collection of alien White Oak species seed in the UK (or Northern Europe) is rendered unsuitable.

b) A further small group of White Oaks (section Mesobalanus) from Europe and Asia are typified by the Hungarian Oak (Q. frainetto) and the Canary Oak (Q. canariensis). They are distinguished by the flowers having long styles and the acorns having a bitter taste. Sometimes included in the previous section with which they will potentially hybridise successfully. This group will also hybridise with each other.

c) Another small group (section Cerris) from Europe and Asia is typified by the Turkey Oak (Q. cerris). In this group the acorns take 18 months to mature and have a very bitter taste. The inside of the cup is also without hairs. The leaves have acute lobe tips which have bristles at the tip.

d) A small and localised group of evergreen species from the South West of the USA and North Western Mexico (section Protobalanus) - is typified by the Canyon Live Oak (Q. chrysolepis). These species have short styles and the acorns mature in 18 months and taste very bitter. The inside of the acorn cup looks woolly. The leaves are, generally, evergreen and have acute lobe tips with bristles.

e) The Red Oaks (section Lobatae) are an American group of, both evergreen and deciduous, species occurring from Canada right down the Continent to the northern part of South America. The styles are long; the acorns take 18 months to mature and they taste very bitter; the whole nut is encased in a thin, papery skin. The inside of the cup looks woolly. The leaves have acute lobe tips with bristles. Although these may hybridise with one another they do not usually hybridise with White Oaks and so can usually be collected in the UK with more confidence.

 

The tropical and subtropical, sub-genus Cyclobalanopsis is entirely evergreen but does contain a few species hardy enough for cultivation in cold temperate climates - occasionally good specimens of the Japanese Q. acuta and the Himalayan Q. lamellosa are found in favoured warmer situations in the UK – especially where late season frosts are infrequent. This group does not show any dormancy condition.

 

The acorn is normally dispersed in the autumn when the nut is separated from the cup either by the action of frost or strong winds. The nut is a well developed substantial structure which can, depending on the species, be as much as 30mm by 20mm and varies in shape from almost cylindrical through conical to nearly round – the base which sits in the cup is rounded and the apex more or less pointed. It consists of a hard pericarp enclosing the contents. The embryo sits at the pointed apical end with the radicle in the tip and the plumule vertically below it and the whole enclosed by two large fleshy cotyledons which contain the food reserve.

 

As the acorns mature the pericarp of the seed hardens and turns colour from green to brown. They can, however, be collected successfully from the tree when they are still just green when they can be chilled and/or germinated. The critical feature is to maintain the water status.

 

The food store consists chiefly of carbohydrates but also proteins and lipids and at dispersal the seed has a relatively high water content – up to 55 or 60% in White Oaks and usually about 15 to 20% in Red Oaks. Drying, as would be anticipated, leads to a deterioration in viability and consequently any storage should be conducted under water conserving conditions at low temperatures. Ideally White Oaks should be put into the germination process as soon as possible and only stored in the short term.

 

Acorns, being large seeds, are best not stored in bulk as they are likely to heat up as a result of normal metabolic activity and so should be kept in small units in all but the short term.

 

The White Oaks, in general, produce good crops of seed annually unless there are untoward weather conditions. They do not exhibit any dormancy controls and the germination process will normally commence straight away after the acorns are shed - if conditions are satisfactory. The radicle emerges fairly quickly but the plumule tends to delay until temperatures begin to rise in the spring.

 

The Red Oaks tend to produce good crops of seed intermittently and there can be several years between bumper crops. Crops in the intervening years are usually of poor quality and often have high levels of Weevil (Curculio spp) infestation. The acorns exhibit an endogenous embryo dormancy which requires a period of chilling for mitigation. The period of chilling varies from species to species depending on the climatic niche that they occupy. For species from the most northerly extremes the chilling period can be as much as 84 days to 56 days in the mid range and as little as 28 days for the more southerly; the threshold temperature for this activity appears to occur at around 5˚C.

 

Acorns are relatively large seeds and they can very easily be station sown by hand. As would be expected, the quality of the seedlings will reflect the polarity of the seed as it is sown – ie it needs to be sown the ‘right way up’ so that the embryo is correctly oriented for maximum growth at emergence. This implies that the seeds are sown with the point down and the hilum scar upwards however as indicated above sowing on the side provides the best outcome. Ideally the seeds should be sown about an inch deep so that any drying of the seed is minimised and when the plumule emerges its base is immersed and provides some stability.

 

Oak seedlings generally produce, initially at least, a taproot system and it would be prudent to maintain this in the early stages of growth to achieve maximum development during the first season. Hence to avoid circling in the bottom of the pot or container it would be sensible to use a narrow, deep container which might also allow for air pruning at the base. At some subsequent stage it will probably be necessary to prune the tap root in order to encourage the development of a fibrous root system.

 

Acorns vary in size annually as a result of the climatic conditions during the preceding summer – particularly the level of light and temperature and this is reflected in the amount of food reserves made available to the seeds. The acorns from any one tree will also vary in size about a mean in any year. The following examples give an idea of the range of average seed counts per kilogram (taken at the season of seed dispersal):-   Q. cerris - 320-350 (in 1975 which was a good summer - the seed size increased to 220), Q. ilex - 440-500, Q. palustris - c1,0000, Q. petraea – 280-300, Q. robur - 240-260, Q. rubra - 300-320 and Q. suber - 320-360.

 

Seedling growth in the first season is often limited – evergreen types often only making 15cm of stem height but some Red Oaks are more vigorous and will achieve 40 to 50cm.

 

Oaks will also need to make mycorrhizal associations - so this condition should be catered for at germination.

 

The chief setback to seedling growth, in temperate climates, can be the development of an infection by Oak Powdery Mildew (Microsphaera quercina) – which will effectively cause the cessation of growth for the season.

 

Lithocarpus

 

Lithocarpus is an extensive genus of evergreen ‘Oaks’ which are chiefly native to the tropical and subtropical laurel forests of South East Asia. However a few species occur in more northerly locations and these provide species which will grow in warm temperate climates. Many of the species are very decorative. Of the warm temperate species, several can be found growing reasonably well in collections in the warmer niches of the British Isles – particularly the Japanese Lithocarpus edulis, L. henryi from Central and South-western China and L. pacyphyllus from the Eastern Himalayas.

 

They produce seeds which are similar to an Oak acorn but which develop a woody shell. However seed production in the UK is often limited in quality and quantity by poor summer light and cool temperatures; it thus requires a ‘good’ summer for virtually any crop to be produced – despite adequate pollination. It should also be born in mind that the parent tree will need to be sufficiently well established and have reached a mature condition.

 

In common with all subjects in this family the seeds should not be allowed to dry out and must be kept under moisture conserving conditions to maintain best germinability. The seeds do not exhibit any dormancy controls and will germinate reasonably quickly when sown if the temperature is high enough (18+˚C). The seeds can be sown individually in suitable containers - and with the correct polarity will produce good quality seedlings. These will not be frost hardy when young.

 

Notholithocarpus

 

The monotypic genus (Notholithocarpus densiflorus) has been created to accommodate the Tan Oak from the West Coast of the United States – it was conventionally included in Lithocarpus although it was the only representative of this genus from outside Eastern Asia. Recent genetic and DNA investigation has indicated that it is not closely related to Lithocarpus or any other genus of the Family – it is probably closest to Quercus - and has therefore been given its own genus. It is a common and sometimes dominant tree in the forests of the Coastal Ranges across to the Sierra Nevada chiefly in California and Southern Oregon. It is capable of growing to more than thirty metres tall. Currently the populations are being decimated by the spread of the fungus disease ‘Sudden Oak Death’ (Phytophthora ramorum). It is an evergreen tree and the leaves are hard, tough and persistent with a covering, when young, of brown scurfy hairs.

 

It is a species which will succeed in the South of the UK and will fruit successfully. The fruits are very similar to the Oaks insofar as a single acorn type seed is produced in a cup – which is distinctly ‘spiny’. The seed takes eighteen months to mature to dispersal. The acorn has a very hard woody shell.

 

If the seed does not dry significantly germination of fresh seed is relatively easy. The seeds are collected from the ground and are graded to take out the smallest and the empty or infested seed is removed by flotation. The seeds can be stored in the short term under water conserving conditions at low temperature.

 

For germination the seeds are fully imbibed and then sown when about half the seeds may emerge erratically and over a long period. A synchronised and rapid emergence will occur at high levels of productivity if the imbibed seeds are chilled for 56 days at 3˚C and then germinated at 18 to 20˚C when emergence will occur in about 21 days.

 

 

Castanea

 

The genus Castanea (the Sweet Chestnuts) contains eight or nine species of often substantially sized, deciduous trees and shrubs. They are native to the Northern Hemisphere with species of local importance in Europe, Asia and North America where they can be the climax vegetation in temperate deciduous woodland. Virtually all have significance as timber trees and the European Castanea sativa has been selected and cropped for its edible seeds.

 

The fruit has a spiny case (a ‘burr’) which encloses the seeds, this case splits at maturity to release the seeds - these can be picked up from the ground. Each fruit (in most species) may contain up to three seeds.

 

The seeds are relatively large and, generally, are variable in size – depending on the suitability of the season for food storage, the number of seeds which develop in the case, any inherent periodicity and other inherent genetic characteristics of the tree.

 

Depending on requirements, it would be prudent to grade the seeds as there is much evidence to show that bigger seeds produce bigger seedlings. As the seeds are large it would be useful to place the seeds in water so that ‘floaters’ can be eliminated – as these are likely to be non-viable.

 

The chief cause of subsequent poor performance will be the loss of water from the seed and this can have a detrimental effect as the food reserves are principally lipids and proteins. It is therefore necessary to store the seed under water conserving conditions or to process the sample into the chilling procedure as soon as is feasible after collection. The seeds are prone to surface infection by ascomycetic fungi and should therefore be surface sterilised (dilute hypochlorite) before storage – even at low temperatures.

 

The seed can be cold stored, under water conserving conditions, for several months – taking care to store in such a way that ‘heating up’ is avoided.

 

The imbibed viable seed has a variable chilling requirement (depending on the provenance of the sample) but is usually about 63 days at 3˚C. Germination is most productive at 15-18˚C. The main issue with successful treatment is to ensure that these relatively large seeds do not come under any water stress as they tend to ‘use’ quite a bit of water. Thus the samples should be monitored regularly and the medium remoistened as necessary. The seeds can also chit a low temperatures so this regular monitoring should include assessing this feature and sowing as soon as this happens. (Do not mix seeds from different sources as they may have different chilling requirements).

 

Castanopsis

 

Castanopsis is a genus of evergreen trees and shrubs which is limited to Eastern Asia and is chiefly tropical and sub-tropical in its distribution. There are however a few species with a temperate provenance of which C. cuspidata from South Korea and southern Japan is most commonly seen in the UK.

 

The fruits are like a hard beechnut which contains one seed - which resembles an acorn but with three longitudinal ridges. These are shed from the split fruit case in the autumn. The seeds do not show any dormancy controls.

 

Fresh seed should be stored at cool temperatures under water conserving conditions in the short term and the imbibed seed germinated at 18-20˚C when emergence should be synchronised and take in the order of 21 days.

 

Chrysolepis

 

This genus Chrysolepis (the Chinquapins) consists of only two species, both are evergreen – one growing to tree stature (c30m) and the other a small shrub. They are native to the West Coast of North America and were once included in the genus Castanopsis. They are distinguished by their simple, entire, linear leaves which have a dense layer of golden scales on the lower surface and which persist for three or four years.

 

The fruits are produced in dense, green, prickly cluster which mature to a light brown. The fruits consist of a cup like structure densely covered with spines which more or less encloses the seeds – like a chestnut, this contains three seeds.

 

Seeds take two seasons to mature before dispersal in the second autumn after a spring/summer pollination

 

Natural regeneration of both of these species from seed, throughout the natural range, is extremely sparse or even non-existent although there is prolific and often extensive regeneration over a large area from root sprouts. Success under artificial conditions is also very variable. The number of viable seeds in a sample rarely exceeds 50% and although these can be germinated quite easily - the survival rate subsequently is very low and it is possible that the seedlings may require to engage in a mycorrhizal association at an early stage. It also appears that pruning of the tap root is counterproductive.

 

The seeds do not exhibit any particular dormancy conditions and germinate when temperatures exceed c15˚C.

 

Fagus

 

The Beeches consist of a genus (Fagus) of eight to ten species with a circumpolar distribution in the Northern Hemisphere and occur in temperate climatic areas. They are often dominant forest trees in their particular climatic and geographical areas viz - F. sylvatica, F. orientalis and F. grandifolia and are important timber trees. The following species are also seen in cultivation in the UK:- F. crenata, F. engleriana, F. japonica and F. lucida.

 

The beeches are the classically quoted example of periodic seed production, as they generally only produce substantial seed crops intermittently – usually between four and seven years. This production will depend on the quality of the summers and hence the quantity of stored food which is achieved.

 

Common Beech (F. sylvatica) will produce populations of seedlings with a relatively high proportion of coloured leaf seedlings if selected from parents with coloured leaves (ie shades of red and ‘purple’). F. sylvatica is also grown in the UK for hedging and as rootstocks for grafting the wide spectrum of clonally reproduced variants.

 

The relatively inconspicuous flowers are produced at leaf bud break, are wind pollinated and the fruits mature by the same autumn. The fruit is a cupule and this encloses one to three (generally two) seeds. The seed is dispersed when this nut splits to liberate the seed. If the fruits are readily accessible, it is simplest to pick the nuts just before they are ready to split and gently dry them to liberate the seeds – otherwise they can be picked from the ground before the critters get them. It is only worth collecting the seeds in good ‘mast’ years as the seeds in the ‘off’ years will be mostly empty and of low quality.

 

The seeds are pyramidal in shape about 10mm by 6mm at the base. Although beech seeds will withstand drying more than most of this Family, it will be prudent to maintain the water status and cool store them until required as there is inevitably loss of viability with drying.

 

The seeds have a dormancy which is mitigated by chilling - however there is no consistency to the duration of the period required. It is said that the variation between years and between samples can be as little as four weeks to a maximum of twenty weeks. As the chilling requirement appears to vary so significantly about the norm (which is postulated at nine weeks) the usual practice is to chill the seeds at 3˚C until 10% of the radicles emerge and then transfer to conditions for germination.

 

The temperature for successful (ie synchronised and speedy) germination is relatively low (+/-15˚C) – high temperature appears to hamper productivity significantly.

 

The seeds are big enough to handle individually and so can be station sown. Polarity does have an impact and the seeds should be sown on their side as the radicle is at the tip.