Coniferales

 

Podocarpaceae

 

This family of evergreen conifers is probably the least settled in its taxonomic clarity in spite of the modern availability of DNA analysis and expert assessment. The determination of relationships and hence the naming of genera and species is still somewhat confused – at least to the layman. In the past the all-embracing genera of Podocarpus and Dacrydium covered a lot of sins but at least they provided a place to hide and provided recognisable names! In recent decades the family has been much revised and there has been much ‘splitting’ and as many as twenty generic names have appeared. Fortunately most of the genera and species found in this family are natives to warmer climates than that experienced in the British Isles, are not suitable for cultivation here and so do not concern these notes.

 

Although this family constitutes the third largest family in the Coniferales, it is hardly known by growers in Europe and the temperate Northern Hemisphere largely because it is fundamentally a Southern Hemisphere group of plants – the centre of diversity being in Australasia – it does however range into Africa, the western side of South America and above the equator to China and Japan and the great majority of the genera and species have distributions in tropical and sub-tropical climates. Because of this unfamiliarity and access to habitat, the family has largely been ignored by European and North American taxonomists. However there are several species which do have a distribution in temperate climates – especially in the temperate rain forest areas of South America and New Zealand and these provide some notable ornamental subjects for milder climatic areas in the British Isles.

 

The Family is diverse in morphology and ecology. The structure of the fruits however is fairly constant and, superficially at least, shows a close relationship with the Yews (Taxaceae) – usually they consist of a few seeds carried on fleshy, often colourful scales.

 

The following list of genera seems to provide the best shot at the current (2012) state of play:- Acmopyle, Afrocarpus, Dacrycarpus, Dacrydium, Falcatfolium, Halocarpus, Lagarostrobus, Lepidothamnus, Manoao, Microcachrys, Microstrobus, Nageia, Podocarpus, Prumnopitys (to include Sundacarpus), Retrophyllum, Saxegothea and Parasitaxus (which is unusual insofar as it is the only known parasitic plant in the Coniferales – it is native to New Caledonia and parasitizes other podocarps). Phyllocladus has proved difficult for the taxonomists to categorise as it sits uncomfortably in this Family and is fairly distinct from other podocarps – it is thus sometimes accorded its own family by some taxonomists.

 

Relatively few of this family are satisfactorily cultivated in temperate climatic conditions but nevertheless those that are suitable provide a number of ornamental trees and shrubs.

 

In general there is little detail recorded on the conditions required for germination in this family and little if any critical work has been undertaken. Seed of any relevant species is rarely available in the British Isles either because of the unsuitability of the climate or most probably because there is rarely more than one specimen of a particular species in any collection - and as many of the genera are dioecious - there is no chance of reproduction!

 

All the Podocarps make an obligatory mycorrhizal association and this is of the vesicular-arbuscular type. Most of the genera produce a fleshy fruit which is dispersed by frugivorous birds and consequently the seeds are usually protected for passage through the gut of the bird by a hard seed coat – which may then present a problem for the propagator.

 

The genus Microcachrys is monotypic and is represented by M. tetragona – an endemic of Tasmania having a limited distribution to the Western Ranges. The plant is a virtually prostrate growing, evergreen shrub with whipcord like foliage and branchlets on which the leaves are carried in four ranks.

 

The plants are monoecious with the male and female cones being produced on separate branches. The female flowers have numerous fertile scales – between 20 and 28 – each of which has the potential to develop one seed. These then become enclosed in a red fleshy aril and the whole fruit develops and resembles a small mulberry about 6 to 8mm long.

 

The seeds are extracted from the ripe arils by maceration in warm water followed by a period of fermentation until the seeds fall and the dross and liquor can be decanted off. The seeds have a hard seed coat which must be made permeable – usually by an extended warm water soak.

 

The seeds benefit from a brief chill (28 days at below 5˚C) in order to synchronise and speed germination.

 

The monotypic genus Saxegothea (S. conspicua) is a South American native – where it is found in dense temperate rainforest on the lower slopes of the southern Andes in both Chile and Argentina - in association with Nothofagus dombeyi and Fitzroya cupressoides. It is a slow growing tree of yew-like appearance and habit – growing into a conical tree to 11 or 12m – but sometimes much taller. It however shows only limited tolerance of cold conditions, despite its southern provenance, and is therefore only suitable for the milder climatic niches of the UK – it does reasonably well in Devon and Cornwall. It was introduced by William Lobb in 1847 – for Messrs Veitch of Exeter – so it is perhaps not surprising that the largest and oldest specimens are found in the far South West.

 

The trees are monoecious, the male flowers are produced in the leaf axils near the tips of the branchlets and the female flowers are solitary and terminal on different branches. The female cones mature by the first autumn after the spring pollination and consist of flattish, triangular, pointed, overlapping, fleshy scales – which overall present an irregularly globose outline.  The cones are 15 to 20mm long with the fleshy grooved scales carrying two seeds each – an individual cone will develop between 6 and 12 seeds.

 

The seeds are hard shelled, ovate, about 3mm long and glossy brown. There is little definitive information on the regeneration characteristics of this species – most plants sold in the UK, up until the last decade or two, have been propagated vegetatively from cuttings but these take many years before they develop a dominant leader and as they are slow growing anyway the problem is compounded. With the increase in interest in Chilean flora, of recent years, it has been possible to obtain seed commercially and various seed collecting expeditions have also been successful.

 

Germination will initially depend on the imbibition of the seed and this will depend on developing the permeability of the seed coat. This can be achieved either by an extended warm water soak or by a reasonable period of warm, moist stratification – this latter procedure may be more effective as it is not clear whether the embryo in this species is fully mature at dispersal. After this process the sample will benefit from a short chill (28 days at below 5˚C) which will synchronise and speed germination when it is subjected to conventional temperatures.

 

Despite its recent decimation, the genus Podocarpus is still a very large genus with an extensive geographical distribution in the Southern Hemisphere and up into Eastern Asia. A few of the species however are suitable for cultivation in the British Isles but generally only in the favoured climatic niches of the South and West. There are rarely sufficient numbers to allow the production of seed.

 

Pollination is in the spring - the cylindrical male cones are found along the branches - and in P. totara, at least, the pollen is ejected vertically, from the ripe cones, in a concentrated cloud in the first part of the morning as temperatures rise – quite a spectacular sight in its own right. The female cones occur usually terminally on the branches, they consist of 2 to 4 scales only one of which develops a seed and the remainder together with the top of the stalk fuse and develop as a brightly coloured, fleshy, edible structure much like an aril.

 

The fruits are picked when soft and ripe and are then macerated in warm water and allowed to ferment until the seeds will separate and sink to the bottom of the container when the liquid and dross can be decanted off.

 

The seed is an oval, nut-like structure with a thin, fleshy outer seed coat and a hard bony inner seed coat. The hard seed coat certainly prevents imbibition of the seed until such time that it is sufficiently degraded to become water permeable. This can be achieved by an extended warm water soak if the seed is fresh or an adequate period of warm, moist stratification which would also complete any embryo immaturity present.

 

The hardness of the seed coat could well vary from species to species as often a particular bird is responsible for taking the seed and so dispersing it - and the hardness of the seed coat has evolved to achieve a satisfactory passage through the activities of this particular gut without damage but still degrading to the point of water permeability.

 

There does not appear to be, in general, any encumbrance to germination requiring mitigation by a period of chilling for the great majority of the genus but this should not be ruled out in a species at the extremes of temperate climate distribution, such as P. macrophyllus in the north and in the south it certainly benefits the speed and synchronisation of emergence (35 days at below 5˚C) in the New Zealand, Podocarpus totara.

 

As seed is usually difficult to find it is necessary to import seeds and it would be prudent to purchase from a supplier with access to fresh material or a collector.

 

Good sized specimens – some of them over one hundred years old - of the following species can be found in the South West of England (and similar climatic niches elsewhere in the British Isles):- Podocarpus salignus (Chile), P. macrophyllus (China and Japan), P. totara (New Zealand) and P. nubigenus (Chile) but seed production is, to all intents and purposes, non-existent. Podocarpus alpinus (Tasmania) and P. nivalis (New Zealand) are both hardy, montane species – as low growing, evergreen bushes and grow satisfactorily in all but the coldest parts of the British Isles.

 

The genus Prumnopitys is currently confirmed as separate from Podocarpus and now includes what used to be called Podocarpus andinus which has become Prumnopitys andina. It is a montane species from Southern Chile with a high alpine distribution, it can develop into an evergreen tree 12 to 15m tall. It is reasonably hardy and fairly widely cultivated in the UK. The trees are usually dioecious but are sometimes monoecious. It is most easily distinguished by the aggregation of one to several single seeded fleshy scales fusing to form a fruit which resembles a small damson or bullace. The fruits are dispersed by birds and the seed is hard coated. This species is from Southern Chile and germination is enhanced by chilling the imbibed seed for 35 days at below 5˚C, after the seed coat has been reduced.

 

The old portmanteau genus of Dacrydium has been severely split and of those species which could possibly be cultivated in the British Isles D. bidwillii (the Mountain Pine of New Zealand) has become Halocarpus bidwillii; D. franklinii (the Huon Pine of Tasmania) is now Lagarostrobus franklinii; and D. laxifolium (the Mountain Rimu of New Zealand and the smallest and lowest growing known conifer) is designated Lepidothamnus laxifolius - while D. cupressinum (the Rimu of New Zealnd) remains in Dacrydium.

 

These genera are largely defined (and thus separated from Dacrydium) on the basis of the arrangements of the structures within the female cone but all are similar to Podocarpus in that they produce fleshy fruits which are dispersed by birds and have a hard (horny) seed coat. This implies a similar approach to achieving germination.

 

The genus Phyllocladus is included within the Podocarpaceae but is regarded by many taxonomists as sufficiently distinct to be attributed to its own family.

 

Phyllocladus species are evergreen trees and shrubs which are native to Tasmania, New Zealand, the Philippines and Borneo. They are readily identified by their leaves being reduced to small scales with the branchlets flattened into broad leaf-like structures – the phylloclades. The genus currently contains eight species – principally in New Zealand.

 

The plants are dioecious or monoecious and the flowers are carried on the margins of the phylloclades. The female cones are very small and consist of single erect seed carried on a single short fleshy scale – in some species there are several together in a cone-like body. The seeds are oval, nut-like (to 8 or 10mm long) and relatively large, at least twice as large as the swollen scale and resembling an acorn in its cup.

 

The fruits are picked individually and macerated in warm water to separate from the fleshy scale – leaving to ferment if necessary to achieve separation and for the seeds to fall to the bottom of the container.

 

The seeds are relatively hard seeded but can be made permeable with a warm water soak. No further treatment is needed to effect germination.