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The families of gymnosperms |
This data set is generated from a DELTA database (Dallwitz 1980; Dallwitz, Paine, and Zurcher 1993). Intended primarily for development as a teaching resource, it currently comprises descriptions of the extant families of Gymnosperms (including Gnetales), with taxon and wood-anatomical character illustrations; interactive identification and information retrieval using the program Intkey; and source references for the descriptive data and illustrations. There are illustrations of nearly all the genera and many species. Many of the ‘technical’ illustrations reflect the indifferent quality of the original line drawings, but they are supplemented with Zoya Akulova’s permission by photographs from her recent postings at calphotos.berkeley.edu. 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.
Anyone interested in extant Gymnosperms should consult C.J. Earle’s Web site (www.conifers.org). This provides comprehensive, detailed, illustrated descriptions of species, genera, families and higher groups, information on modern taxonomic research, phytogeography and ecology (etc.), references, and Internet links. However, it does not offer direct facilities for identification. Our Intkey package shows what could be done in that direction.
Comments and other input would be welcomed and acknowledged. The data could be donated to any person or institution interested in developing them further. The data could readily be extended to the levels of genus and species.
The data could also be extended to incorporate extinct forms. Such an undertaking should repay the effort, since the Gymnosperms as a group merit study, not only because of the ecological and economic significance of extant forms, but also by virtue of their well documented fossil record. Before 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, linking ancient and extant forms. For example, 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 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 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.
Revised 5 August 2019