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Development and interpretation of nectary organs in Ranunculaceae11Dedicated to Prof. Dr. Werner Rauh on the occasion of his 85th birthday (May 16, 1998).

1999; Elsevier BV; Volume: 194; Issue: 3 Linguagem: Inglês

10.1016/s0367-2530(17)30920-9

1618-0585

Claudia Erbar, Stephanie Kusma, Peter Leins,

Plant and animal studies

The nectary organs in the flowers of many Ranunculaceae - intercalated between perianth and androecium - are commonly considered as derived from stamens. The homology of both structures is seen in the peltation, i. e. in the formation of a cross zone at the ventral side of the organs. Since detailed investigations have shown that stamens do not develop as peltate leaves (Leins & Boecker 1982), this proof becomes invalid. The very differently shaped nectary organs of Helleborusfoetidus, Ranunculusficaria, Aquilegia vulgaris, and Aconitum napellus can be reduced to a common early stage of development which is characterized by the formation of two basal-lateral bulges at the ventral side of the primordium (Fig. 57). In Helleborus and Ranunculus these bulges become connected with each other to a transverse protuberance. In Helleborus intensive growth of the transverse protuberance being laterally connected with the elongating dorsal part of the primordium results in a tubular nectary organ with the nectary at the base of the tube. In Ranunculus the transverse protuberance develops more or less free from the margins into a scale protecting the nectary. In Aquilegia and Aconitum a connection of the basal-lateral bulges does not take place; the nectary is translocated into a spur turning dorsally above the lateral protuberances. The onto genetical studies show that nectary organs in the Ranunculaceae are not peltate structures in the usual sense because they do not result from a continuous expansion of the margins of the primordium and subsequent fusion at the ventral side like in peltate leaves. Only in Helleborus there is sometimes and especially in older stages a continuum between margins and the ventral protuberance(s). We think, however, that we now have a new piece of evidence for a relation of the ranunculaceous nectary organs with stamens: the initially more or less free basal-lateral bulges (which become connected in Helleborus and Ranunculus) can be interpreted as rudimentary (sterile) adaxial pollen sacs (Fig. 58). The relation between the nectary organs and stamens in Ranunculaceae may be seen as a result of an overlap of the genetic programs of the perianth members and the stamens.