The families of gymnosperms

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L. Watson and M. J. Dallwitz

Introduction

This embryonic data set is generated from a DELTA database (Dallwitz 1980; Dallwitz, Paine, and Zurcher 1993). It currently comprises descriptions of the extant families of Gymnosperms (including Gnetales), with taxon and wood-anatomical character illustrations; facilities for interactive identification and information retrieval using the program Intkey (including hints on using this to best effect); and source references for the descriptive data and illustrations. The taxon illustrations portray nearly all the genera and numerous species, but many of them reflect the indifferent quality of the originals. There is copious published information on the anatomy of conifers (softwoods), but our present data and illustrations have mainly been taken from Phillips’s (1948) world-wide account, cross referenced with a recent interactive treatment of northern hemisphere species (A.G. Heiss: www.holzanatomie.at). That gymnospermous leaf blade anatomy is a potential source of numerous interesting and taxonomically useful characters for extant forms was shown early last century by Florin (1931 onwards), but his pointers in that direction seem never to have been followed up by acquisition of the requisite comparative data.

Persons seriously interested in extant Gymnosperms are referred to C.J. Earle’s excellent and taxonomically authoritative Web site (www.conifers.org). Although this provides comprehensive, detailed, beautifully illustrated descriptions of species, genera, families and higher groups, in addition to copious information on modern taxonomic research, phytogeography and ecology (etc.), references, and Internet links, it does not offer direct facilities for identification. This present, modest Intkey package is intended to exemplify what could be done in that direction, cf. our ‘Families of flowering plants’ and other packages available at delta-intkey.com. Constructive comments and expert, specialist input would of course be welcomed and appropriately acknowledged. Alternatively, the DELTA and associated files could be donated to any person or institution interested in developing them further. We emphasize in this connection that the ‘Families of Gymnosperms’ DELTA data are easily accessible for making corrections and improvements aimed at improving and extending them, and they could readily be extended to the levels of genus and species.

The data set could also be extended to incorporate extinct forms. Such an undertaking should repay the effort, since the Gymnosperms as a group merit study by all serious biology students, not only because of the ecological and economic significance of extant forms, but also by virtue of their well documented fossil record. Prior to the recent advent of DNA comparisons, the absence of Angiosperm fossils dictated that likely evolutionary sequences and taxonomic groupings for the dominant group of extant Seed Plants had to be deduced exclusively from comparative morphology and anatomy, with some outside assistance from phytochemistry and cytology. By contrast, palaeobotanists have published a wealth of comparative morphological and anatomical data for Gymnosperms, incontravertably linking ancient and extant forms. For example, informed taxonomic botanists have long contended that the widespread evolutionary theme of precocious maturation (known to zoologists as ‘neoteny’) has predominated in both groups of seed plants; but in the Gymnosperms, shell-proof evolutionary sequences have long been guaranteed with reference to the fossil record. Thus, Rudolph Florin’s painstakingly detailed demonstration of the origins of coniferous female cones and of their ‘ovuliferous scale complexes’ is as compelling and as intellectually satisfying as the far more widely publicized example of the evolution of the horse’s foot. In some respects, it is more so, because the chemical properties and relative indestructability of plant cell walls permits acquisition from compressions and petrifactions of exquisite anatomical and histological details of extinct organisms that are unavailable for vertebrate animals. The remarkable accessibility of plant material for anatomical comparisons between extant and ancient forms is further exemplified in comparative studies of leaf cuticles from cycads, commenced by Thomas and Bancroft in 1913, which led to recognition of the two distinct lineages now recognized as the Orders Cycadales and Bennettitales.


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