The Gymnosperms represent a recognisable group of plants with particular botanical affinities – most fundamentally all produce ‘naked’ seeds – from flowers which develop into structures which are described as cones. They appear in evolutionary terms after the Ferns and before the Angiosperms. Their classification into Orders and Families has been the subject of much debate over the last couple of decades but recent advances in DNA analysis and its interpretation have clarified most of the relationships and in consequence many surprising and unexpected realignments of taxonomic units have been created. The importance of this in taxonomic terms does not directly concern these notes (except in terms of nomenclature) but the real affinities and relationships of genera and species do have relevance in seedling production - insofar as close relationships are likely to have evolved down similar avenues in terms of both anatomical and morphological development and physiological responses. These developments will have been influenced by the environmental and ecological conditions preceding, surrounding and affecting germination during the evolutionary process.

 

The Gymnosperms consist of four Orders - the most significant and numerous being the Coniferales; in addition are the Gingkoales – represented nowadays only by Gingko biloba, the primitive Cycadales and the Gnetales.

 

The affinities of the plants in their Families are relevant to the plant propagator as they may well provide clues to potential similarities in relation to seedling production, seed structure and composition, seed handling, dormancy conditions of the seed, the environment for germination and seedling development. These similarities may provide indications for the handling and treatment of less well known subjects where direct information is lacking – as closely related subjects are likely to have developed similar characteristics. In this respect a tendency to the storage of oily food reserves, immature embryo conditions, hard seed coats and endogenous dormancy all appear to have evolved in closely related patterns.

 

The seeds of conifers are relatively simple in structure – the embryo is carried vertically in the seed usually with the radicle close to the base. The embryo is embedded in, and supported by, the endosperm. These food reserves are more often than not high in fats and oils – which has implications for the provision of storage conditions (loc cit) of the seeds. Usually the cotyledons are numerous but this is not invariably the case and in some genera – especially at the more primitive end of the spectrum - there may be only two or three.

 

In general the presence of a morphologically immature embryo condition in this group of plants is uncommon but it seems to occur more frequently earlier in the evolutionary tree rather than later viz Gingko and Taxus. Its mitigation however is just time consuming and simply requires the provision of warm conditions for the imbibed seed to mature. Elsewhere among the conifers the presence of an immature embryo, although requiring the same conditions for mitigation, is much more marginal and is often a function of physiology rather than morphology.

 

A few species have developed genuinely impermeable seed coat conditions but in the great majority of cases this is a hard seed coat rather than a tough condition and can usually be mitigated by an extended warm water soak. Seeds with such a condition, even marginally, also tend to enhance the condition in dry storage. Although the hard seed coat condition is not common among conifers it does occur as a protective strategy in those genera where the seeds are dispersed in a fruit which is attractive as a food source to mammals or birds (eg Taxus and Juniperus). Thus the ‘hard’ coat provides protection for the seed while in passage through the gut – by the time the seed has passed through the gut and is expelled in the faeces, the seed coat has become degraded and is usually no longer impermeable and the process proceeds to chilling or germination without the encumbrance. In the absence of a suitable pet bird or mammal to undertake the activity, these species will require a suitable protocol to eliminate the condition artificially.

 

The seeds of conifers are not, in general, subject to an endogenous embryo dormancy condition which requires a period of chilling for mitigation. However there is, among several species from cold temperate climates, the presence of such a control in the seed. This control is not definite or constant and can vary in its intensity from year to year, sample to sample and indeed can vary within a sample. It is usually not sufficient to prevent germination within a sample – and this may occur without chilling but the germination process will usually be slow, erratic and incomplete.

 

The variation in this situation occurs, it would appear, because the agency causing the encumbrance develops fairly haphazardly in the endosperm and/or the seed coverings. This can be demonstrated by excising the embryos and finding that they will germinate without delay. The presence of this block to germination can be mitigated by, usually, a fairly short period of chilling. The presence of this block to germination is part of the evolved ecological strategy for encouraging germination to occur during an advantageous window of opportunity - as many of the seeds of such species are shed over a reasonably long period from the autumn to early spring and it is feasible that any deep seated condition would not be satisfied.

 

An effective dormancy is also developed by the seeds of many species (which do not necessarily exhibit endogenous embryo dormancy) by the requirement for a high threshold temperature for germination – for while low temperatures persist germination of the imbibed seed is effectively prevented and emergence is delayed until there are suitable conditions for development and survival of the seedling.

 

In general conifers from warm temperate, subtropical and tropical provenances do not exhibit any constraints to the germination process; however species from temperate, cold temperate and subarctic climates often have developed strategies for preventing germination at unsuitable seasons so that germination is promoted at the best possible time for survival of the seedling.

 

Many species of conifer are native on soil types with a poor nutrient status – especially phosphorus – and have adapted to succeed and compete under these conditions by developing mycorrhizal associations. When propagating species with this necessary requirement – especially under protected conditions (where natural inoculation by spore rain is potentially impaired) - it will be prudent to provide a relevant inoculum to the growing medium.

 

The conifers represent an important group of ornamental plants and although the great proportion are variants which are propagated by vegetative means – many of the species (which are ornamental or of interest in their own right) are readily and economically produced from seed.