Comments are presented on the continuing need for a better taxonomy of ferns as a basis for experimental studies of all kinds; some aspects of the ecology of Malesian ferns are also considered.

Five mixed populations of Dryopteris dilatata and D. filix-mas have been studied in deciduous woods near Derby, England. It has been shown that in selected populations of each species, the plants were significantly clumped. It has also been shown that small plants of each species in all populations tended to grow amongst bryophytes, whilst larger ones grew in a wider range of habitats. All populations of D. dilatata showed an excess of small, sterile plants over larger, fertile ones. All but one of the D. filix-mas populations showed an excess of large, fertile plants over small, sterile ones, while the remaining one showed roughly equal numbers of large, fertile plants and small sterile ones. The population dynamics of two populations of each species have been studied so far over two seasons. This has shown that plants may increase or decrease in size or remain the same size between years. Mortality has been shown to be very size-specific in that smaller plants have a much lower chance of survival. Colonisation by new plants was mostly in bryophytes near established plants. The significance of these observations for the population dynamics of the species is discussed.

While only in its infancy, the application of electrophoretic analysis in studying the evolutionary biology of pteridophytes is proving to be of considerable value. Since the technique identifies subtle differences in protein structure, it can generate an improved picture of the genetic composition of organisms. To date electrophoresis is (1) providing us with new information about the structure of the pteridophyte genome, (2) interfacing well with laboratory studies of breeding system mechanisms to indicate that some pteridophytes are predominantly outcrossing species, and (3) generating genome-specific markers for detecting hybrids and analysing patterns of evolution. Electrophoretic data suggest that species of Bommeria are very distinct from one another and may not be congeneric. Further, enzyme characters indicate that the sexual Bommeria species have maintained a mechanism to promote outcrossing in populations, in spite of the limitations that this breeding system places on colonising ability. In Cystopteris, electrophoretic markers are of value in deciphering species relationships and origins, especially among neopolyploid taxa. The indication in Cystopteris that extant diploids are outcrossing may help to explain the complex systematic patterns that currently exist within and among its taxa. Further investigations may demonstrate that similar mechanisms are prevalent among other systematically challenging ferns and fern allies.

An unusual form of Asplenium adiantum-nigrum from Scottish and European serpentine sites has been grown for several years under uniform conditions of culture alongside A. adiantum-nigrum of nonserpentine origin, and has been found to retain its characteristic features. The morphological distinctiveness of both types, apparent in juvenile as well as adult plants, has been maintained through successive generations.

Transplant experiments were carried out in order to determine whether serpentine and non-serpentine plants differed also in their physiological response to soil factors. The results suggest that serpentine soils are unfavourable to the growth of non-serpentine A. adiantum-nigrum, particularly at germination and during the early development of the sporophyte. Soil analysis data are presented and briefly discussed.

The experimental evidence presented here, combined with the constancy of the diagnostic differences leading to ease of recognition of the serpentine forms at all ages, suggests that evolution leading to the establishment of ecologically adapted divergent strains is actively in progress.

Polystichum muricatum hybridises with both P. polyphyllum and P. speciosissimum on the Cerro de la Muerte in Costa Rica. Both hybrids are intermediate between their two parents in most of the assessed characters. True indusia, which are fully developed in P. muricatum, vestigial in P. polyphyllum, and absent in P. speciosissimum, are intermediate in mean development in both hybrids. However, one sorus is likely to have either a fully-developed indusium or a vestigial indusium. False indusia are characteristic of P. speciosissimum, but are vestigial to absent in its hybrid with P. muricatum. False-indusium development appears to behave as a recessive trait in the interaction of P. speciosissimum with P. muricatum.

Environmental disturbance has played a major role in the development of hybrids in Costa Rica. Mixed populations of the parent species are more common in disturbed terrain than in pristine areas, and hybrids are found only in disturbed terrain; this suggesting that disturbance promotes hybridisation.

The number of fern species in various countries in the Old World tropics is examined and explanations for very rich and very poor fern floras are given. Borneo and New Guinea are the two richest areas, with an estimated 1000 and 2000 species respectively; the difference in number is probably due to the much greater area of land at high altitudes in the latter. Aspects of geographical and ecological speciation in the genus Grammitis within New Guinea are discussed, and the means by which such speciation may have been promoted are outlined.

Information on the ecology of tropical hybrid pteridophytes is extremely scarce, and, indeed, a very small number of hybrids are known in these habitats.

Some questions and examples relating to this problem are posed, as seen in the New World tropics.

The most common kinds of speciation result in new species that initially have a small range. These will develop a limited or an extensive range depending upon the geographic extent of the environment to which they are adapted. A significant element in the extent of the potential range of a new species is the adaptation inherited from the parental species. Selection of a parental species for a local environment at one site can lead to a narrow ecological adaptation and often to a limited potential range. These species are likely to produce derived ones that also have a limited range, and these derivates will increase the regional species endemism and diversity. Selection of a parental species for migration to other sites can lead to a broader ecological adaptation and often to a broad potential range. These species are more likely to produce derived ones that also have an extensive range, and these derivates will increase regional species diversity.

Perennial indendent gametophytes of Hymenophyllaceae, Vittariaceae and Grammitidaceae are a well-known phenomenon in the eastern United States. Their persistence is attributed to the ability of gametophytes of these fern families to reproduce themselves vegetatively via gemmae. This paper reviews the biology of independent gametophytes of these families as they exist in the eastern United States and presents new evidence from enzyme electrophoresis regarding their identity and origin.

Autecology of pteridophytes may be refined by defining the plant community and habitat, and phytogeographic occurrence, of the species studied. Work with Blechnum spicant in the Pacific Northwest, and with Lorinserea areolata in the Southeastern U.S.A. has uncovered autecological differences for these species across habitats differing in overstory and hydrology. Natural history observations are necessary to suggest the most appropriate hypotheses to investigate objectively. A modification of Daubenmire's Canopy-Coverage method provides a grid across which many factors may be recorded or tested in repeatable objective manner. Such an analysis was used to test the association between L. areolata life-history classes and hummocks in hardwood swamps. Contingency tables were used to disprove the null hypothesis that L. areolata was distributed randomly with regard to hummocks. Hummocks were thus ‘safe sites’ for the completion of the life-cycle of L. areolata, and additional considerations of safe sites for Lygodium japonicum and Dryopteris ludoviciana are introduced. Analysis of biomass and coverage of Onoclea sensibilis where it is very abundant suggests that it is highly susceptible to competition where it shares plots with L. areolata. The concept of the optimum habitat with regard to abundance of the taxon, frequency of the habitat-type, successful reproduction, and susceptibility to competition between similar life forms is discussed.

The radiation of species in Papuasia, particularly in the mid-montane zone, offers a natural laboratory in which to study the processes of speciation in tropical ferns and fern allies.

Some of the major problems associated with the interpretation of altitudinal zonation of pteridophytes in Papuasia are outlined.

Water deficiency is the key factor limiting the occurrence of pteridophytes in seasonally dry tropical areas and shaping their adaptive strategies in respect of habitat preferences, life-forms, phenological patterns, and reproductive biology. In Zambia, which is situated in the savanna woodland zone, a total of 146 pteridophyte species occur mainly in special habitats: extrazonal evergreen forest patches and initial successional stages of lithoseres and hydroseres. Life-forms with perennating buds well protected against desiccation (hemicryptophytes and geophytes) dominate, while those with more exposed buds (epiphytes, chamaephytes and phanerophytes) are much less numerous and restricted mainly to the higher-rainfall areas. Selaginella tenerrima represents the life form of a therophyte, unknown in any other pteridophyte genus. Three major seasonal patterns of growth and dormancy may be distinguished: the evergreen type (ca. 40% of species), the poikilohydrous type (ca. 20%) and the deciduous (‘summer-green’) type (ca. 40%). No less than 20% of species are able to survive recurrent bush-fires, and some of them possess the features of advanced pyrophytes. In the driest parts of the savanna zone in Africa, e.g. in the Lake Chad Basin of northeastern Nigeria, seasonal pools are remarkably rich in water ferns, especially of the genus Marsilea which has undergone an intensive adaptive radiation in this environment.

Since they first evolved, pteridophytes have been subjected to attack by micro-organisms and arthropods. Present-day ferns are associated with a complex array of, not only phytophagous, scavenging, predatory and parasitic arthropod species but also fungi, bacteria, viruses and herbivorous mammals.

Recent research has tended to stress the importance of secondary plant chemistry in deterring feeding by herbivores and attack by pathogens. Although ferns have a more limited chemical repertoire than the angiosperms, many of the classes of secondary compounds isolated from ferns have been shown to have anti-microbial and anti-herbivore activity under both laboratory and field conditions. Quantitative and qualitative levels are not constant and show great seasonal variation. This chemical variation is important in determining the seasonal patterning of insects and fungi on ferns. New chemical techniques are increasing our knowledge of the biosynthesis and chemical structures of these ecologically important compounds.

Flowering plants show both constitutive and induced resistance as a consequence of herbivore attack. A search for short-term induced chemical responses in ferns have so far yielded negative results in terms of phytoalexin synthesis or direct chemical response to herbivory.

A vegetation survey comprising all major habitats has been used to examine the ecological range of pteridophytes in an area of varied geology, climate and land-use in northern England.

Pteridophytes occur most commonly in coniferous plantations, scrub, cliffs and acidic woodlands and are also frequent in broadleaved plantations, in unshaded mire and on walls and river banks. In marked contrast to the herbaceous angiosperms of the region, pteridophytes have failed to exploit habitats subject to high intensities of disturbance (e.g. arable fields, spoiled land, paths) and are relatively unsuccessful in herbaceous vegetation experiencing moderate intensities of orderly disturbance (pastures, meadows, road verges).

Strategy concepts have been applied to compare the range of ecological specialisation displayed by the pteridophytes with that of the herbaceous angiosperms within the area of study. It is concluded that the contribution of pteridophytes is restricted by the absence of ephemeral and vernal life-forms, the scarcity of shoot systems resilient under defoliation, the low relative-growth rates of many species and the susceptibility of gametophytes, and young sporophytes to competition from herbaceous angiosperms and to submergence by leaf litter from deciduous trees. Whilst some of these features are of recent importance in that increasingly they limit the capacity to survive current changes in land-use, others appear to have restricted the ecological amplitude of the Pteridophyta throughout their history.

The success of plants which lived in the past should be assessed differently from that of living plants as time is an additional important factor. Success may therefore be judged in one period of time or throughout the whole geological history of the plants.

Limitations of the fossil record through plant fragmentation, lack of preservation and incomplete preservation severely restrict the amount of information available. However, accepting these problems, there are four major ways in which plants may be judged: long term survival, repeated specialisation, dominance and adaptability. Examples are given of pteridophytes that exhibit success in these four ways.

The conservational vulnerability of tropical pteridophytes, which make up 80% of the known species, is outlined. Especially threatened are the areas of the world with high percentages of endemism.

Professor Gomez stresses the rate at which the tropical forest, the environment of possibly 80% of known ferns, is projected to disappear over the next 20 years. He asks the question ‘Who will act?’, and intimates that the International Association of Pteridologists (I.A.P.) may take a role in developing a strategy. In the discussion following Gomez' paper, Clive Jermy, Chairman of the I.A.P., summarised the proposals put forward by the Association's Working Party on Conservation (Convenor, David R. Given). As those proposals are complementary to Professor Gomez' remarks and indicate what positive actions are being taken, they are included here.

It is proposed that the Pteridophyta are in many ways the plant kingdom's equivalent of the Amphibia. The biology of these two groups is compared from points which have arisen in this Symposium on the Biology of Pteridophytes. Some areas of possible future development in pteridophyte biology are then suggested.