Biology Reference
In-Depth Information
Chapter 2
A SYSTEMATIC SURVEY OF FLORAL
NECTARIES
GABRIEL BERNARDELLO
Instituto Multidisciplinario de Biología Vegetal (Universidad Nacional de Córdoba-
CONICET), Casilla de Correo 495, 5000 Córdoba, Argentina
1
INTRODUCTION
The construction of classifications, as well as the understanding of biological
diversity, depends upon a careful comparison of attributes of the organisms
studied (Stuessy, 1990). It is widely known that data from diverse sources
showing differences from taxon to taxon are of systematic significance. Dur-
ing the 20th century, systematists have emphasized that their discipline
involves a synthesis of all knowledge (Stevens, 1994) or, in other words, the
variation of as many relevant characters as possible should be incorporated
into the natural system to be constructed. The extent to which particular
characters are constant or labile will determine their usefulness to syste-
matics. In general, more conservative characters will be valuable in defining
families and orders, whereas more labile characters may be useful at the ge-
neric and specific levels (Webb, 1984). There is no doubt that floral
characters are among the most used in the classification of flowering plants.
At the same time, they constitute essential features in diagnostic keys to taxa
in both taxonomic treatments and Floras (Cronquist, 1981, 1988).
The diversification of many plant families has been attributed to adaptive
radiation of pollination and mating systems accompanying changes in eco-
logy and life history (e.g., Grant & Grant, 1965; Dressler, 1990; Barrett et al.,
1996). Reproductive traits in seed plants provide a potentially rich source of
diversity for comparative and phylogenetic studies. When considering the
evolution of the breeding or pollination systems of particular species or genera,
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