Biology Reference
In-Depth Information
Chapter 3
NECTARY STRUCTURE
AND ULTRASTRUCTURE
MASSIMO NEPI
Department of Environmental Sciences, University of Siena, Via Mattioli 4, 53100 Siena, Italy
1
INTRODUCTION
It is easy to define nectaries from a functional point of view: they are plant-
secreting structures that produce nectar, but it is difficult to provide a general
definition. From the anatomical point of view nectaries vary widely in on-
togeny, morphology, and structure (Fahn, 1979a, 1988; Durkee, 1983; Smets
et al., 2000), both between species and within species, depending on flower
sexual expression or flower morph in heterostylous and heteroantheric spe-
cies (Nepi at al., 1996; Küchmeister et al., 1997; Fahn & Shimony, 2001;
Pacini et al., 2003). Intraspecific morphological differences exist between
flowers of the same plant and between plants of the same species with dif-
ferent ploidy (Davis et al., 1996), and morphological characters may be
affected by environmental conditions such as water availability. Petanidou
et al. (2000) found that nectary structure in Lamiaceae species in a Mediterra-
nean shrub community was largely shaped by phylogenetic and climate
constraints. In the course of the flowering season (spring-summer) stomatal
opening and nectary size decreased, thus minimizing nectar flow at a time
when water was scarce. They hypothesized that very concentrated nectar was
secreted via large modified stomata, whereas cuticular secretion was mainly
encountered in species with very thin nectars. Petanidou (2007) speculates
that the frequency of species with stomatal nectar secretion should be much
higher in hot and arid climates like the Mediterranean and deserts than in
temperate ones.
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