Biology Reference
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exist or not), whereas nectary or nectary gland represents a tangible entity
having distinct boundaries (Davis et al., 1998, p. 317).
3.1.6
Colour
Nectaries normally have the colour of the organ where they are located, a
state of affairs that makes it difficult to find them. For instance, in species of
Solanaceae with nectaries on the ovary base, the nectaries are indistinguish-
able from the gynoecium tissue when the nectariferous tissue is green like
the ovary. However, in several taxa the nectariferous tissue can become col-
oured and can therefore be recognized macroscopically, e.g., in the tribe
Lycieae (Bernardello, 1986, 1987) in
Nicotiana
(Cocucci & Galetto, 1992).
This feature has been used to recognize taxonomic groups.
Convolvulaceae species (
Ipomoea
) have either yellow or cream-coloured
nectaries surrounding the ovary base (Collins, 1992). When a mutant with a
green nectary was discovered, it was demonstrated that this colour is inher-
ited as a monogenic dominant trait over the yellow nectary. The colour in
these cases is produced by the presence of carotenoids in the nectary tissue
(Bernardello, 1986; Mann et al., 2000).
On the other hand, environmental variations were reported to be respon-
sible for nectary colour change in
Hedera helix
(Araliaceae: Vezza et al.,
2006). In this species, the nectary is situated above the inferior ovary and its
colour varied from green to brown during the flowering period, a change
resulting from the accumulation of anthocyanins in subepidermal layers of
the parenchyma; the authors suggested that with this change the nectary may
protect the inferior ovary from sunlight (Vezza et al., 2006).
3.2
Factors influencing nectary diversity
Floral nectaries are comparatively simple structures that are variable in their
morphology, anatomy, and location (e.g., Brown, 1938; Daumann, 1970;
Fahn, 1979, 1988; Cronquist, 1981; Smets, 1986, 1988; Schmid, 1988;
Smets et al., 2000, 2003). Both phylogenetic and ecological constraints have
been reported to influence nectary traits. These constraints will principally
depend on the plant group, a circumstance that prevents wide generaliza-
tions. Let us examine some particular cases.
In Lamiaceae, nectary structure is shaped largely by both phylogenetic
(nectar volume depends positively on the volume of nectariferous tissue;
Fahn, 1949; Dafni et al., 1988; Petanidou et al., 2000) and climatic constraints
