Coniferales

 

Cupressaceae

 

This family of Conifers is now the largest in terms of the number of genera included (many of which are regarded as monotypic) but it is only about the third largest in terms of the number of species. This family now includes, as a result of the modern assessment of DNA patterns, those genera which were previously assigned to the Taxodiaceae – except for Sciadopitys which is now assigned to its own family. It has a world wide distribution.

 

The taxonomic positions and content of the genera included in this family, because of this modern approach, is still a significant area of debate and the nomenclature is still in a state of flux - as the various authorities make their determinations on the basis of what they think are the important DNA associations and arrangements. However it is now apparent that the Taxodiaceae nest within the Cupressaceae and that it is to be regarded as one big happy family! As far as the propagator is concerned however this is only relevant in relation to the identification of a potential parent and the necessity to be accurate in nomenclature - at least at the genus and species level. This activity has also involved the reassignment and renaming of several important species. It therefore behoves the propagator to determine, with as much clarity as is possible, what is the current name for a particular subject together with any relevant synonyms.

 

Currently (2012) the consensus appears to suggest that the following seven sub-families are recognised and that these contain the listed genera which might be grown in a temperate climate:-

 

Cunninghamioideae - Cunninghamia;

Taiwanoideae -  Taiwania;

Athrotaxidoideae – Athrotaxus;

Sequoioideae - Sequoia, Sequoiadendron, Metasequoia; Taxodioideae -  Taxodium, Glyptostrobus, Cryptomeria;

Callitroideae - Callitris, Actinostrobus, Neocallitropsis, Widdringtonia, Diselma, Fitzroya, Austrocedrus, Libocedrus, Pilgerodendron, Papuacedrus;

Cupressoideae - Thuja, Thujopsis, Chamaecyparis (includes Foikenia), Calocedrus, Tetraclinis, Microbiota, Platycladus, Cupressus (includes Xanthocyparis and Callitropsis), Juniperus.

 

The following five, sparsely represented, sub-families constitute the previously recognised Taxodiaceae and virtually all are survivors of, or are limited evolutionary descendants of, a much wider spectrum of ancient species - with a wider distribution and dominance than their current geographic status suggests.

 

Cunninghamioideae

 

The single genus Cunninghamia constitutes this sub-family and consists of two or possibly three species of evergreen trees and shrubs. It has a limited distribution in parts of southern China and Taiwan. The foliage has considerable similarities with Araucaria.

 

The plants are monoecious and the flowers of both sexes are initiated and develop during the autumn but do not open until the spring when they are wind pollinated. The female flowers are sub-terminal while the male flowers are produced at the tips of the branchlets.

 

The cones develop during the summer season and ripen in the autumn. They are rounded to ovoid in shape, about 40 mm long and wide – often several together. Individually they consist of several leathery scales each of which carries three seeds. The cones ripen and open on the tree, shedding the seeds throughout the winter. The spent cones persist and remain on the tree for several months into the next year. Each cone contains about 30 to 40 scales.

 

The seeds are hard, thin and elliptical – about 4 to 5mm long - and are surrounded by a papery wing. They are similar to those of Sequoia.

 

The germination of a seed sample is hastened and unified by a marginal period of pre-treatment by chilling. Exposing the imbibed seed to a temperature of less than 7ºC for 21 days is normally sufficient.

 

Taiwanoideae

 

The genus Taiwania contains one, possibly two, species (depending on the taxonomic treatment) of very tall evergreen, densely foliaged trees which in outline resemble Cryptomeria but with foliage very similar to Athrotaxis. Taiwania cryptomerioides is found in Taiwan and adjacent southern China and Burma (Myanmar) – although here the variant is sometimes designated T. flousiana.

 

The cones are much like those of Cunninghamia – about 15mm long and 10mm wide and ovoid to cylindrical in shape. The middle 12 to 15 scales are generally fertile and each scale carries two seeds. These seeds are oblong. About 4mm long and are encircled by a membranous wing.

 

Little information is available on the germination characteristics of the seeds but it is reasonable to suppose that the imbibed seed will respond to a marginal chilling of 21/28 days at below 7ºC in order to unify germination.

 

Athrotaxioideae

 

The single genus Athrotaxis is the only genus assigned to this sub-family and contains possibly three species (depending on the taxonomic treatment). These are narrowly endemic in the uplands of Tasmania at considerable elevations (around 1000m). They are reasonably hardy and will succeed in the milder, moister regions of the British Isles – Athrotaxis latifolia has exceeded 15m tall in Cornwall. The genus, in appearance, resembles both Cryptomeria and Sequoia.

 

The trees are monoecious with the sexes developing on separate branches. The cones are globose, slightly tapered at the base and swollen towards the top. Each consists of 18 to 20 tightly packed scales which are woody and wedge shaped with each ending in a spine like process. The cones are held vertically upright on a central axis. The cones in general resemble those of Cryptomeria and mature in the one season. The seeds are small, thin and oblong with two, narrow, opposite wings – much like a Sequoia seed.

 

The cones are picked just before they are ripe and when gently dried and then shaken the scales will have opened sufficiently to release the seeds – these separate readily and so produce a clean sample.

 

Although the imbibed seeds will germinate without pre-treatment the process can be speeded up and unified by subjecting the imbibed seeds to a chilling period of 21/28 days at below 5ºC.

 

Sequoioideae

 

This sub-family contains three monotypic genera – Sequoia, Sequoiadendron and Metasequoia – all of which have value as ornamental subjects – albeit as potentially large to very large, single stemmed, erect trees. They all have a limited and narrow endemic distribution although the last does not now probably occur truly wild. They are all extensively cultivated in the British Isles where conditions are suitable.

 

The Coast Redwood (Sequoia sempervirens) of the Pacific slopes of the Western USA has been widely planted in the UK and succeeds where high winds are not a problem. This tree grows in a very restrictive habitat associated with the summer fog belts on the coastal ranges from mid-California north to the Oregon border. It grows in dense forests – each tree becoming a huge evergreen specimen with a slender trunk, when it is young, and given space, it is a shapely pyramidal to conical tree of graceful habit with downward sweeping branches and shiny deep green foliage. In virgin stands there are groves of trees in excess of 100m tall and over 3500 years old.

 

The small and insignificant flowers are produced from November to March on separate branches of the same tree and although pollination occurs then by wind, actual fertilisation does not occur until May. The cones are pendulous and ripen by September-October to a red-brown colour. They are smallish, oblong in shape and 20-30mm long by 20 mm wide; they consist of several hard, tightly packed, leathery scales – each carrying up to seven seeds, each cone will probably yield about sixty seeds.

 

The seeds are small – scarcely 2mm across, flattish, light reddish brown with a small spongy wing on each side of a central dark tan coloured seed. The quality is usually poor – often viability is as low as 15%.

 

The seeds can be readily extracted by gently drying the cones to open the scales and then shaking or tumbling. Storage by maintaining the seeds at the moisture content at which they were collected at cool temperatures will maintain the viability for several years.

 

There are no dormancy issues and the germination of imbibed, viable seeds at warm temperatures (20-25˚C) will be quick and uniform – usually in 20 days or so. The seedlings develop with two cotyledons.

 

The genus Sequoiadendron is narrowly endemic to California. The single species - the Giant Redwood, Wellingtonia or Big Tree of California – S. giganteum - occurs in a very limited belt on the lower slopes of the Sierra Nevada in California (especially the famous Yosemite National Park). It was introduced commercially by William Lobb for the Veitch nursery in 1853 and the squabbles associated with its naming at that time are legendary!

 

It is a huge evergreen tree with a single erect bole which can reach 80 to 100m tall and with immense girth. In its native habitat it has reached tremendous age (some specimens being 3000 years old). The branches sweep down to the ground carrying their persistent Cryptomeria-like foliage and with its thick, soft, corky bark it is instantly recognisable.

 

The tree is monoecious and the small flowers are produced in April to May and pollination is by wind – fertilisation is then delayed until August - despite the development of the cone. The embryo remains as a few cells only, over the winter and then seed development occurs throughout the following summer when both the seeds and the cone are completed and mature. The cones, which are oval in shape 60-70mm long by 30-35mm broad, mature to a faded reddish brown colour. They are borne singly on the ends of the shoot and remain attached to the tree for many years with the seeds retained inside. The cones dry gradually and open slowly - so liberating the seeds over a considerable time.

 

Young cones can be picked in September-October and gently dried. This action will cause the cones to open and the seeds can be easily released by gently tumbling the cones. The seeds are 3 to 6mm long and compressed to about a thickness of 1mm, the wings are laterally united so that they virtually surround the seed.

 

Germination is markedly inhibited by an endogenous dormancy control. This condition can readily be eliminated by chilling the imbibed seed at 3˚C for 35 days. Even after chilling the seeds will only germinate in a temperature range of 16 to 21˚C.

 

The deciduous, monotypic genus Metasequoia represented by M. glyptostrobioides is another plant which has been described as a living fossil and its discovery in the late 1940s in China and its subsequent ‘escape’ to the West in front of Mao’s Long March advance is also the stuff of legend.

 

It is a tall, erect, single stemmed tree. Because of its relatively recent introduction there have been few mature fruiting trees available but now 70 years on there is no shortage of coning trees (it does produce cones and seed quite successfully at a young age) and seed can be located readily. The tree is monoecious, flowers in the spring and is wind pollinated. The cones are small and pendulous, egg-shaped with thick fleshy scales which eventually dry as they ripen in the first autumn gradually opening to release the seeds. The seeds are 6mm long, flat and obovate in shape, carrying two broad, paper thin, pale wings which are more or less convergent and surround the seed.

 

The cones should be collected at or about leaf fall – before they open, they are gently dried to release the seeds, which will probably need to be cleaned by picking over and removing the cone debris.

 

The seeds will germinate readily when exposed to suitable warm conditions and no dormancy blocks are apparent.

 

Taxodioideae

 

This sub-family contains three genera – Cryptomeria, Glyptostrobus and Taxodium

 

The monotypic genus Cryptomeria is represented by the species C. japonica – the Japanese Cedar or Sugi. It is native to the cold temperate climatic regions of China and Japan and grows into a stately, picturesque, upright, single-boled tree to 35 to 45m tall. It is grown for timber, shelter and ornament and because of the variability many ornamental forms have been selected – most of which are slow growing and/or juvenile foliaged and/or have a contorted habit – and are much used in gardening practice in the Japanese traditions.

 

The trees are monoecious and flower in the spring with the cones ripening in the late summer to early autumn of the same season. The mature cones remain on the tree, opening slowly and releasing the seeds over a long period. The cones are picked when ripe, which is evidenced by the development of a red-brown colour. They are globular (15 to 20mm in diameter) and consist of 20 to 30 woody scales radiating from a central axis. The seeds are extracted by gentle drying to open the scales when the seeds can readily be shaken free – producing a very clean sample.

 

The seed are dark brown, more or less flattened and of an elongated triangular shape – about 4-6mmm long x 3mm wide -

with each edge having a rudimentary wing. Viable seeds contain a relatively large embryo. Seed production is prolific but a large proportion of them are not viable.

 

The seeds can be stored satisfactorily for two years if maintained dry and cool.

 

Germination of virtually all samples of seed is prevented by the development, within the seed, of a reasonably deep physiological dormancy which is mitigated by a period of chilling. This problem can be overcome by exposing the imbibed seed to a temperature below 3ºC for 56 days.

 

Viable seeds will germinate, after such treatment, without significant delay when provided with a temperature of 15 to 20ºC. However the problem of assessing the viability of such small seeds with a high void rate makes the calculation of sowing rates difficult. So the sample is best sown thickly and pricked off – as soon as germination occurs.

 

The monotypic, deciduous genus Glyptostrobus is represented by the species G. pensilis and is closely allied to and is not dissimilar to the genus Taxodium – even to developing the same type of ‘knee formations’ on the roots under relevant environmental circumstances. The species is native to the warmer climatic areas of Southern China although it is possible that it no longer occurs wild. It does not succeed in the UK - except in the very mildest places and is thus rare in cultivation.

 

The cones are pear shaped about 20mm long with a long stem. The terminally winged seeds are about 5-6mm long and are thin coated; they show no barriers to germination once suitable conditions for germination are available although germination does not occur below a temperature of 16˚C.

 

The deciduous, Swamp Cypresses (Taxodium) from the South Eastern USA and Mexico are closely related to Glyptostrobus.

 

They are variously described as three species or as one species (Taxodium distichum) with a series of three geographical variants. They are tall, deciduous, upright, ornamental trees of relatively lightweight structure with a tapering slender trunk. They are particularly adapted to a damp, swampy habitat and on sites where they are regularly inundated they develop unusual aerial roots known as ‘knees’ – which project above the ground.

 

The trees are monoecious and flower in March-April as the leaves expand. Pollination is by wind and the cones mature in the late autumn to early winter of the same year. Two or three cones are, typically, developed in a group towards the ends of the branchlets. They are globose to polyhedral in shape to 30mm+ in diameter, are of a somewhat resinous consistency and ripen from green to purple in colour. They consist of a few four sided scales, each carrying two irregularly triangular, tough coated, woody seeds. On ripening the scales break away from the cone and liberate the seeds. Each cone will produce between 18 and 30 seeds.

 

The cones are collected just as they begin to open on the tree and are gently air dried, they are then crushed to extract the seeds. It is then necessary to separate the seeds from the detritus and because of their shape and structure this is a tedious task.

 

Cool storage under moisture conserving conditions will give a reasonable shelf life of a year or so.

 

Imbibition is initially delayed by the impermeability to water created by the thick woody seed coat but fresh seed which has been dried as little as possible will respond to a warm water soak of 48 to 72 hours. The literature has several ad hoc recommendations to improve the permeability of dried seed but probably the most effective would be a soak in a 1% solution of citric acid for 48 hours.

 

Once the seed has imbibed it requires a period of chilling before germination can be induced. There are many fanciful recommendations in the literature which suggest periods of as much as 90 days – these are almost certainly due to the fact that the seed coat had not been made fully permeable prior to the chilling treatment. This species will usually respond to chilling at less than 5˚C for 42 (even possibly 35) days. Germination is then best at 16 to 20˚C

 

Cypresses

 

The following genera represent what used to be regarded as the Cupressaceae. This group of conifers has a world wide distribution and, in general, develop as upright single-stemmed, conical trees which are clothed to the ground.

 

In general they produce large quantities of seed, but this prolific production is usually associated with a high proportion of non-viable seeds. The cones are remarkably similar throughout the range and typically are small and round (more precisely polyhedral). The seeds are usually small, dry and winged. Most of the species from cold temperate climates exhibit a marginal dormancy condition which is eliminated by a period of chilling. 

 

Callitrioideae

 

This sub-family contains a series of ten genera which are not much found in cultivation in the UK because they are not as competitive ornamentally and/or are less (or not) hardy and/or are best adapted to arid environments - most obviously the Australasian Callitris, the narrowly endemic Actinostrobus from Western Australia, the African Widdringtonia and Neocallitropsis from New Caledonia. All of these are not suitable for cultivation out of doors in the UK and are therefore not described here. These four genera are all closely related and germination of the seeds does not appear to be affected by any dormancy conditions.

 

The old portmanteau genus of Libocedrus (which once was home to a varied, disparate and not very similar group of species in the Cupressaceae) has now been carved up and, as a result of modern DNA assessments, has been scheduled into a series of genera which are often monotypic. In this sub-family are located Austrocedrus (A. chilensis), Libocedrus (4 species), (the non-hardy Papuacedrus) and Pilgerodendron (P. uviferum). Calocedrus has now been transferred to the sub-family Cupressoideae with its associated species – the most relevant being C. decurrens.

 

All of these genera are basically limited to a warm temperate or sub-tropical distribution but those which border on the cooler margins can be grown in warmer moister niches of the British Isles. Although germination of these species will be achieved without pre-treatment, a speedy and synchronised emergence will occur if the imbibed seed is chilled for 35 days below 5˚C and then subjected to above 18˚C for germination – however for the successful germination of Austrocedrus the chilling requirement is effectively mandatory.

 

The remaining two genera Fitzroya and Diselma are closely related and are the only two with a cold temperate distribution.

 

Diselma archeri is a monotypic genus from Tasmania. It is an evergreen bush or small tree and is rarely seen in cultivation. It would appear that it can be raised without problem – germination is said to be straightforward.

 

The monotypic genus Fitroya is one of the most interesting of conifers insofar as it is the largest and potentially the oldest conifer in the Southern Hemisphere. It is found on both flanks of the southern Andes in Chile and Argentina where it is native to the region of temperate rain forest. In its native habitat it can reach immense size – on a par with Sequoiadendron – and specimens of 3500 years old are known. In cultivation in the UK it is quite rare and is only suited to sheltered moist environments. It was first introduced by William Lobb in 1849 for Veitch and again it was later sent back by Richard Pearce for the same employers. There are still some specimens of this vintage extent – most notably at Killerton.

 

It shows considerable variation in its sexual expression – various trees being dioecious, monoecious or even rarely hermaphrodite. The flowers are pollinated in the spring and the cones mature in the autumn of the same season – however as female trees will cone without pollination and fertilisation, it is likely that any seeds will not be viable – in the UK it is rare to find other than a single specimen at any one site so that even when sexually mature there will be no potential partner extant – if there was - Murphy’s Law ordains that they would be of the same sex!

 

The cones consist of nine scales arranged in three whorls, the scales of the lowest whorl are minute and sterile, the middle whorl is normally empty but can produce the odd seed and the upper whorl of scales which are the largest and bear two to six, two or three winged seeds. The cone is woody and 6 to 8mm in diameter and terminates in a resin producing body which produces a fragrant smell.

 

The cones open readily when ripe and should be collected just before this stage as the colour changes from green to brown. They open with air drying and the scales flare out and the seeds can be shaken out easily to produce a clean sample.

 

The seeds are long, narrow and flat – about 4mm long – with usually two, broad half moon shaped wings. Much of a sample is non-viable.

 

Viable seeds do not exhibit any particular problems with germination although very limited experience does suggest that a short chill will synchronise and speed emergence.

 

Cupressoideae

 

Microbiota is a monotypic (M. decussata) genus from the Far East of Western Siberia in North East Asia, it is a small, low growing, spreading, evergreen shrub. It is mainly used as a ground cover plant in dry, depauperate hostile environments. In its native habitat it is reported that it rarely exceeds 50cm high.

 

The plants are monoecious and the cones are the smallest among the conifers – only some 2 to 3mm long. They are produced in the one season after pollination in the spring – they ripen from green to brown. They consist of four scales arranged in two opposite pairs. The seeds are roundish to oval and are not winged. Usually there is only one seed per cone.

 

Germination is unified by chilling – a period of 42 days at below 5˚C is adequate.

 

Perhaps the most striking realignment, produced as a result of the DNA assessment in this part of the family, is the confirmation that the Chinese Arborvitae – most commonly known as Thuja orientalis - is (as had already been widely suspected) more closely related to Microbiota and Tetraclinis than Thuja and is now finally separated into the genus Platycladus.

 

Platycladus orientalis is a relatively small, slow growing tree often with a number of trunks from the base.

 

The species is monoecious. The flowers develop in the early part of the year and pollination occurs in March to April.  The male cones are small – 2 to 3mm long and yellowish green. The female cones are produced terminally on the shoots and develop in one season, dehiscing in the autumn. They are fleshy and pale greenish blue when immature and red brown when mature. They consist of six sometimes eight scales – the middle four are fertile; the proximal pair carry two seeds each and the distal pair one each. The scales are fairly thick and woody when mature and if picked before dispersal, the scales spread wide and dehisce readily, when air dried, to liberate the seeds. The seeds are virtually wingless about 3 to 4mm across.

 

Germination is synchronised by a short period of chilling (35 days at below 5˚C) but dormancy is also achieved by the seed requiring a relatively high temperature to initiate germination (optimally between 18 and 20˚C).

 

Tetraclinis is a monotypic genus - T. auriculata which is native to the Western half of North Africa, Malta and sparsely in southern Spain. It grows into a conical, erect, evergreen tree to 12 to 15m tall and is a particularly valuable, ornamental conifer for the hot dry extremes of a Mediterranean climate area.

 

It is monoecious and the cones are produced solitarily on the tips of the branchlets in the spring. The cones ripen in about eight months when they become brown, they are broadly globular, 10 to 15mm in diameter and consist of four tough thick scales arranged in opposite pairs. The outer pair are sterile and the inner, narrow pair are fertile and carry two or three seeds each.

 

The cones should be collected just before dehiscence and then dried at reasonably high temperature (35 to 40˚C) when the cones will dehisce and liberate the seeds. Viability is not normally high.

 

The seeds are about 6mm long, 2mm wide and oval with a broad papery wing on each side.

 

There are no particular blocks to germination although best results for a speedy and synchronised germination are achieved at temperatures above 18 to 20˚C.

 

Calocedrus is one of the genera which have been devolved from the once all encompassing Libocedrus - which had become a portmanteau name for a fairly disparate collection of cypress type conifers.

 

This genus has, as a result of DNA assessments, finally been separated out and consists of the Californian Incense Cedar (C. decurrens) and the Chinese C. macrolepis (from Southern Yunnan) together with its two sub-tropical relations (?variants) C. formosana and C. rupestris. Only C. decurrens is suitable for cultivation in a cold temperate climate and is, in fact, much hardier than its Mediterranean climate provenance would suggest.

 

The Incense Cedar (C. decurrens) tends to grow, in the UK, as an erect, columnar tree to well over 30m tall – although on the West Coast of the USA it eventually develops a spreading crown. It has striking dark green foliage.

 

The female flowers are produced during the spring on the tips of the branches – pollination is followed by fertilisation and the cones mature in the same autumn. The trees are monoecious and seem to self fertilise without difficulty.

 

The cones are oblong-conical in shape about 25mm long and consist of six narrow, long, overlapping scales which open to disperse the seeds in the late autumn. The seeds are flattened with a substantial wing and are carried one pair to each of the two fertile middle scales – one with a large wing and one with a small wing – the actual seed being about 6mm long.

 

The cones should be hand picked in the autumn just before dispersal - when they will readily open with conventional air drying. When they are tumbled the seeds fall out easily and a good clean sample is produced.

 

Seed stored, without further drying, at cool temperatures will maintain viability for several years.

 

Virtually all samples of the seed of C. decurrens show a marginal dormancy condition which is eliminated by chilling. A chilling treatment of 35 days at below 7˚C will unify the germination response. Rapid germination requires a temperature of above 16˚C.

 

The genus Cupressus is a widespread group of tall evergreen trees. They occur principally in the warm temperate climates of the Northern Hemisphere fringing to the cold temperate range. There are more than twenty species which are divided into the New World Cypresses – many to several species (depending on the taxonomic treatment) usually with restricted distributions – and the Old World Cypresses – with a relatively few species ranging over quite large areas through the north of Africa and Southern Europe through to South East Asia; in addition what used to be called Chamaecyparis nootkatensis is now included in this genus. They are in general decorative subjects and would be more widely grown as ornamentals but for the occurrence of the microfungal disease, Coryneum cardinale, which disfigures (usually causing large brown blotches) and then ultimately kills the tree. Fortunately the disease has not, so far, become particularly virulent in the climate of the UK.

 

The trees are monoecious with the male and female flowers being produced in the autumn and pollination occurring over the winter; the cones then mature over eighteen months and ripen in the later part (July onwards) of the second summer. The mature cones are some 25 to 30mm in diameter, woody to leathery in texture and globular (polyhedral); the scales open at the sutures after drying to liberate the seeds. In those species which are native to ecological niches which are regenerated by wildfire many of the cones are serotinous (remain closed) until opened by the passage of a significant degree of heat – although these cones will remain on the tree for several years the viability of the enclosed seeds is not maintained for more then a few years. All the species are prolific come producers.

 

The cones are collected, during the late summer just prior to opening. The cones do not open easily with artificial drying but if the cones are frozen for two days and are then subjected to a drying environment at 30 to 35˚C the cones will open and the seed is readily shaken free. Each cone will have the potential to yield between 12 and 15 seeds – depending on the species and pollination success.

 

The quality of the seed, in terms of viability, is almost invariably low but existing viability can be maintained for a few years at cool temperatures.

 

Although germination of the seeds of all species will occur without any pre-treatment, a period of chilling will both speed and synchronise emergence. Storage of the imbibed seeds for 35 days at below 5˚C will achieve the required effect.

 

The seeds of C. nootkatensis often develop a marginal, hard seed coat condition which can prevent imbibition – this can be mitigated by a warm water soak for 48 hours prior to chilling.

 

Cypress seeds have, in general, a considerable propensity to develop fungal infections and it would be prudent to consider dressing the seeds with a fungicide but this should be undertaken with care – bearing in mind the probable need for the seedlings to develop a mycorrhizal association.

 

The Junipers (Juniperus) are a large and widely distributed genus of evergreen conifers varying from procumbent shrubby alpine and montane types to tall, erect, single stemmed forest trees. They are chiefly found in the sub-tropical and temperate climates of the Northern Hemisphere but are found below the Equator in Africa. The number of species currently tends to be under review - as the determination of what constitutes species and subspecific rank is argued through - but somewhere between 50 and 70 is the current range!

 

They are generally a highly ornamental group which lend themselves to intensive cultivation. Many species tend to be variable and have given rise to an enormous selection of ornamental forms – these are inevitably vegetatively propagated.

 

The fruit of this genus is unusual and is distinct among the conifers insofar as it is effectively a berry – the flesh of which is a source of various useful oils and chemical products and in the case of J. communis provides the flavour to gin (Geneva)!

 

The plants flower in the spring and as the cones mature the scales become fleshy and coalesce to form an indehiscent berry-like fruit containing one to four seeds. According to the species, the plants are dioecious or monoecious and the fruits take one, two or even three seasons to ripen to maturity. The seeds are taken and dispersed by frugivorous birds. The berries are usually blue, black or red-brown (the colour is species specific) when ripe and are covered in a waxy pruinose bloom. Depending on the period taken to maturity, fruits of the previous seasons occur on the same branch.

 

The fruits should be picked as soon as they are ripe – before they are taken by birds. The seeds are extracted by soaking the seeds for a few days in warm water, then macerating and leaving to ferment until the pulp floats off and the seeds fall to the bottom of the container. Some species have an oily flesh which repels water and militates against successful fermentation; such seeds should be soaked in brine for two or three days when the flesh will begin to separate. It is important to persevere with the cleaning of the seeds as any residual flesh may still contain a germination inhibitor.

 

The seeds are protected by an impermeable hard seed coat – this has evolved to protect the seed in its passage through the digestive tract of the bird – although, as a result of this progress, the coat is massively degraded and in nature there is not much further degradation required before the seed can imbibe.

 

As the fruits are of different vintages on the same branch and ripening rates are variable, it is necessary, for ease of preparation, to pick the fruits by hand – selecting only the berries in the relevant condition.

 

After extraction and washing to provide clean seeds, they are surface dried, air dried for a couple of days and then they are stored, under moisture conserving conditions, at cool temperatures – this maintains viability for several years. Commercial samples of seed are often offered as dried berries but the treatment is the same beginning with an extended warm water soak.

 

Most samples of seed, in common with so many of the Cypresses, usually show a high proportion of non-viable seeds – this is normally associated with a failure to develop an endosperm.

 

This genus exhibits some of the most comprehensive dormancy controls found among the conifers, a significant range of species show the development of a hard seed coat and/or an embryo dormancy requiring a period of chilling for its elimination; some species also produce germination inhibitors in the flesh of the fruits. The degree of dormancy control also varies within a species - where it occurs over a considerable range of climatic experience. There can be less chilling and often greater hardseededness in warmer provenances. The picture is also complicated by the possibility of the embryo being immature at dispersal.

 

In order to be reasonably certain of achieving a reasonable degree of success in a prescribed treatment sequence – the relevant phases of the following defined sequence should be applied. If no relevant data is available then use the treatments outlined:-

a) extraction of the seed from the fleshy fruit – ensuring the production of a properly cleaned sample;

b) reduction of a hard seed coat to a permeable condition – depending on the degree of hardseededness - either by a prolonged warm water soak or digestion with a 4 to 6 day soak in 1% citric acid solution;

c) the maturation of the embryo by warm stratification of the imbibed seed sample at 22˚C for 42 days;

d) a chilling treatment of 70 days at below 3˚C;

e) the provision of a germination environment of at least 16˚C.

 

The literature suggests that most temperate species have the same sequence of controls but vary in the period required to overcome the individual dormancy condition – however as usual some periods quoted seem to be extraordinarily long and outside their natural environmental parameters which suggests that the previous treatment was not completed adequately.

 

The following species are known to exhibit significant levels of hardseededness – J. chinensis, J. communis, J. horizontalis, J. occidentalis, J. osteosperma, J. pinchotii and J.scopulorum, while J.ashei, J. deppeana, J. monosperma and J. virginiana do not. Most of the species from cold temperate distributions can be expected to require a chilling treatment to break the endogenous dormancy and species from warm temperate regions may still require chilling at below 7˚C for 28 or 35 days.

 

The genus Chamaecyparis consists of tall, erect, conical, evergreen Cypresses which are normally clothed to the ground in flat dense foliage. They constitute a very ornamental series of species - which is typified by the Port Orford Cedar or Lawson’s Cypress (C. lawsoniana) – in which virtually all the species show a fair degree of variability in size, habit and foliage colour. There are six species in the genus and these occur on the far Western side of the United States (C. lawsoniana and C. thyoides) and Eastern Asia (C.obtusa and C. pisifera from Japan, C. (Fokienia) hodginsii from Eastern China and the less hardy C. formosensis from Taiwan). They are all important as timber trees and as ornamentals. (C. nootkatensis has been realigned in Cupressus).

 

Because of their ability to remain clothed to the ground they are widely used as hedging plants – C. lawsoniana especially. The considerable variability in size, shape and leaf colour, which occurs in this species, has given rise to many vegetatively propagated variants but it has also been possible by judicious selection to determine parent trees which will produce a population of seedlings with particular coloured foliage.

 

The flowers are produced in the spring on the tips of the branches, both sexes on the same tree. The cones are small, spherical (polyhedral) to about 12mm in diameter. They mature in the late summer to early autumn of the same year – they consist of 6 to 12 scales – each scale with a potential to produce 5 seeds.

 

The cones should be hand picked just before they begin to open and are gently dried at about 30˚C – the scales will then open at the sutures and the seeds can be shaken out. Each cone will normally yield between 20 and 30 seeds. The seeds are small, flat and winged and naturally are dispersed by the wind over the course of the winter. If the cones do not open readily – as often happens with C. thyoides – the scales can be induced by soaking the cones, draining and then freezing them and then returning them to the drying process.

 

Storage at low temperatures under water conserving conditions will preserve viability for several years. The quality of the seed is intrinsically low – normally below 70% an often as low as 45%.

 

Germination will occur without subjecting the seed to any pre-treatment but under these conditions is usually erratic and over an attenuated period. A unified and synchronised emergence with a rapid response can be induced if the imbibed seeds are stratified at 5˚C for 35 days. The less hardy C. formosensis does not need to be chilled and a satisfactory emergence will be achieved if the germination temperature is maintained in the range of 18 to 20˚C.

 

Thuja – the Arborvitaes are a widely cultivated, but small, genus of tall, ornamental evergreen trees, which although producing useful timber, are extensively used in temperate climates as a hedging plant and because of their variability are clonally reproduced to create a wide spectrum of decorative cultivars varying in shape, size and foliage colour.

 

There are five species (the previously designated T. orientalis is now shown, as a result on DNA observations, not to be closely related and is placed in the separate genus Platycladus). Two species (T. occidentalis and T. plicata) are found in North America and three species (T. koraiensis, T. standishii and T sutchuensis) are distributed in Eastern Asia.

 

The trees are monoecious and the male and female flowers are borne on separate branches or twigs they develop in the autumn but pollination does not occur until the following spring. The female cones mature by the autumn of the same year. The cones are ovoid – about10 to 15mm in length and are made up of relatively few scales (3 to 10 but 12 in T. plicata). During the summer the cone gradually turns colour from green through yellow and buff to cinnamon and finally brown - the overlapping scales become thin, flexible and leathery. Usually only about two or three pairs of scales are fertile and each carries up to three seeds underneath. The seeds are winged with a pair of thin lateral wings.

 

In the two North American species - T. plicata and T. occidentalis - the seeds are about 6mm long, flat and round – consisting of lateral wings surrounding an elongated centrally sited seed.

 

Once the cones are mature – ie they have just turned from cinnamon to brown - they should be picked and then air dried. The cones will then open readily and the seeds will shake free, producing a clean sample. Drying should not be continued for any longer than is necessary to separate the seeds, as they lose viability if they dry more than marginally. In common with so many cypresses the habit of prolific seed production is accompanied by a low viability. Storage under cool water conserving conditions will prolong existing viability for considerable periods.

 

If the seeds are sown without pre-treatment the germination response can be quite variable – as even marginal drying seems to cause erratic and attenuated emergence; however pre-treatment with a period of chilling (for 35 days at below 5˚C) will synchronise and speed germination at temperatures in excess of 16˚C.

 

The monotypic genus Thujopsis is represented by T. dolobrata – a Far Eastern species from Japan. It is rarely grown from seed as it such a variable plant in terms of size and habit.

 

The cones are globose in shape, upright on the branches and about 15mm in diameter. They are composed of 8 to 10 thick, fleshy scales - the top and bottom of which are sterile and dry to a hard leathery consistency. The seeds are carried four or five to a scale, they are fat and oblong with two narrow wings. The cones open readily on drying and the seeds can be shaken free.

 

No pre-treatment is normally required for a satisfactory germination.