William G. Chaloner’s research while affiliated with Royal Holloway University of London and other places

Living with fire is a challenge for human communities because they are influenced by socio-economic, political, ecological and climatic processes at various spatial and temporal scales. Over the course of 2 days, the authors discussed how communities could live with fire challenges at local, national and transnational scales. Exploiting our diverse, international and interdisciplinary expertise, we outline generalizable properties of fire-adaptive communities in varied settings where cultural knowledge of fire is rich and diverse. At the national scale, we discussed policy and management challenges for countries that have diminishing fire knowledge, but for whom global climate change will bring new fire problems. Finally, we assessed major fire challenges that transcend national political boundaries, including the health burden of smoke plumes and the climate consequences of wildfires. It is clear that to best address the broad range of fire problems, a holistic wildfire scholarship must develop common agreement in working terms and build across disciplines. We must also communicate our understanding of fire and its importance to the media, politicians and the general public. This article is part of the themed issue ‘The interaction of fire and mankind’.

Fire has been an important part of the Earth system for over 350 Myr. Humans evolved in this fiery world and are the only animals to have used and controlled fire. The interaction of mankind with fire is a complex one, with both positive and negative aspects. Humans have long used fire for heating, cooking, landscape management and agriculture, as well as for pyrotechnologies and in industrial processes over more recent centuries. Many landscapes need fire but population expansion into wildland areas creates a tension between different interest groups. Extinguishing wildfires may not always be the correct solution. A combination of factors, including the problem of invasive plants, landscape change, climate change, population growth, human health, economic, social and cultural attitudes that may be transnational make a re-evaluation of fire and mankind necessary. The Royal Society meeting on Fire and mankind was held to address these issues and the results of these deliberations are published in this volume. This article is part of the themed issue ‘The interaction of fire and mankind’.

Competition for survival in Devonian and Carboniferous plant communities evidently favoured an increasing proportion of K-type reproductive strategies rather the r-type homosporous reproduction of the earliest vascular plants. This pressure for a greater food reserve, first in the megaspore and subsequently in the embryo itself, inevitably led to a polyphyletic rise of heterospory and eventually to the seed. Probable pathways of seed evolution are represented in a range of Palaeozoic megaspore-bearing structures. New material of Archaeopteris latifolia from the Devonian of Pennsylvania shows significant variability in the number of megaspore tetrads per sporangium (2–5) and in abortions of individual members of the tetrad. This material reduces the gap between typical Archaeopteris and the early seed, Archaeosperma.

Three aspects of palynology in which core questions remain unanswered are reviewed. These are (1) the function of the huge range of types of exine sculpture of iso- and microspores that they share with many of those seen in angiosperm pollen; (2) the selective value of multiple apertures in eudicot pollen; and (3) the worldwide spread of very similar striate bisaccate pollen, apparently derived from at least three separate and very different gymnosperm plant groups in the Permo-Trias, when the macrofloras of that time show such strong biogeographic segregation.

Ricciisporites tuberculatus Lundblad is a prominently sculptured palynomorph that is permanently united in tetrads. This palynomorph has a wide geographic distribution and reaches a stratigraphically important acme in the Late Triassic of Europe, Greenland, and Arctic Canada. This palynomorph has not yet been found in situ in a fossilized reproductive structure, and consequently its botanical affinity is unclear. Some authors have suggested that R. tuberculatus was produced by a seed plant, but others have suggested that this palynomorph was produced by a liverwort comparable to Riccia. In order to clarify the botanical affinity of R. tuberculatus, we have analyzed its morphology using SEM and TEM. Individual grains within the tetrad are equipped with a single distal colpus, and the ultrastructure of the palynomorph wall is characterized by a granular inner sexine and an electron-dense laminated nexine. These morphological features ally R. tuberculatus to the gymnosperms. The combination of strongly ornamented monocolpate pollen grains permanently united in tetrahedral tetrads is unusual and to the best of our knowledge has not been reported previously in a gymnosperm. This may represent an extinct strategy to promote the fertilization of several archegonia in an ovule leading to simple polyembryony.

The evolutionary sequence from homospory through heterospory to the seed habit is reviewed in terms of the “small spore” (miospore) part of the life cycle. In the early stages of this progression, as seen in the Devonian and Carboniferous, the miospore shows little outward modification. The earliest miospores to function as pollen grains still retained proximal germination via a triradiate suture. The term “prepollen” is redefined so as to cover all such cases in which the miospore behaved as a pollen grain (in that its corresponding megaspore was retained in a ovule) but in which the germinal aperture was still proximal. The change from proximal to distal germination, which evidently lagged behind the retention of the megaspore to form an ovule, occurred independently in the cordaites and pteridosperms. The behavior of the pollen in living cycads shows an intermediate state between that of prepollen and the true pollen of the living conifers; for although the germination of cycad pollen is distal, the eventual release of the sperm is proximal.The change from the (distally) monocolpate to the ubiquitous triaperturate pollen in the angiosperms took place during the Cretaceous. One possible route of derivation is represented by the trichotomocolpate aperture present in the pollen of a few living angiosperms. The behavior of this type of pollen at germination shows that it may function as though having either one distal or three equatorial apertures.

During a low sea level stand and wet climate phase at the end of the Mississippian, Lower Palaeozoic limestones at the northern edge of the Illinois Basin were karstified. The caves and fissures that formed were infilled subsequently with clastic sediments of Pennsylvanian age (late Bashkirian–early Moscovian (= Atokan, Duckmantian/Bolsovian, Westphalian B/C)). The earliest infills comprise organic-rich, almost coaly, sediments, while sands, silts and fine clays were deposited subsequently. The sediments are fossiliferous and contain abundant plant fragments, most notably cordaitalean and conifer remains. Many of the plants and megaspores are uncompressed and have undergone minimal thermal alteration. Charcoal occurs throughout the sedimentary infills but is most abundant in the later deposits, where conifer remains predominate. These conifers are currently amongst the oldest known from North America. The presence of cordaitalean remains in the earliest coaly infills is supported by the detection of specific fernane derivatives. The lipid extract of the cave fill sequence contains polyaromatic hydrocarbons (PAHs), such as pyrene, chrysene, benzo[ghi]perylene, and coronene, which distribution further attests to the importance of wildfire in preserving the plant remains.

With the ubiquity of flowers in our everyday lives, it is sometimes easy to overlook their central importance in the production of food and other materials on which human survival depends. The origin of flowering plant (angiosperm) diversity, which is intimately connected to the diversification of