Annonaceae, Magnoliaceae, and Schisandraceae in Magnoliales); however, nectary
location and structure are quite diverse, including petal nectaries, large glands on
the base of filaments, and stigmatic nectaries (Fig. 7) [14, 105].
Septal nectaries are widespread in monocots, although absent in the largest
family – Orchidaceae (Figs. 7 and 8a) [14, 99, 113, 124–127]. They rarely occur
outside monocots and are a result of incomplete fusion of a small region of the carpel
margins [9, 14, 99]. Perigonal nectaries are second-most common type of nectaries
in monocots and may be epidermal as well as trichomatous [99]. Some authors
suggest that perigonal nectaries may have evolved from septal nectaries by
heterochrony, but further studies are necessary to confirm this hypothesis [14,
128–130]. The absence of the septal nectaries or the emergence of perigonal and
staminal nectaries are related to alternative pollination modes (e.g., buzz pollination
in some Asparagales) and attraction (e.g., floral deceit in Dioscoreales) [14, 99,
128–130].
Receptacular nectaries first emerged in the early divergent eudicots. However,
nectaries on petals, staminodes, and carpels also occur in this lineage (Fig. 7) [14,
105]. Within the order Ranunculales, nectar spurs are very noticeable; these are
extensions of various parts of a flower that produce and store nectar (Fig. 8b–c) [14].
In Delphinieae (Ranunculaceae), for example, the nectar spur is formed by
the postgenital fusion of two primordia of the internal perianth whorl and is linked
to the pollinator’s proboscis length [131]. Therefore, morphological variation of
these structures is highly correlated with the type of pollinators and the reproductive
success of individual plants [132].
Distinct receptacular nectaries are common in the core eudicots (Figs. 7 and 8d),
but in flowers with inferior ovary or narrow corolla tubes, they seem to become lost
in the course of evolution [105]. The presentation of nectar through these structures
has many advantages, like the increase of the nectar volume and its constant
production during anthesis, improving the attraction of pollinators [105]. Developmental studies have demonstrated that CRC (crabs claw) expression is required for
nectary development in core eudicots [133] (Fig. 7). This gene is linked to the
regulation of carpel development in early lineages of plants, but its expression in
nectaries of derived lineages suggests a tendency of change from the typically
peripheral perianth position of the nectary in basal taxa to central positions associated with reproductive organs in eudicots [133].
3
Osmophores
The presence of odor is related to the production of volatile oils by secretory
structures located inside or on the surface of vegetative and/or reproductive
organs [134]. In some plants such as Ceropegia (Apocynaceae), Aristolochia
(Aristolochiaceae), and species of Orchidaceae and Araceae, the odor production
is restricted to certain areas of the floral organs, where the cells generally differ
structurally from their neighbors.
28 Diversity of Floral Glands and Their Secretions in Pollinator Attraction
721
location and structure are quite diverse, including petal nectaries, large glands on
the base of filaments, and stigmatic nectaries (Fig. 7) [14, 105].
Septal nectaries are widespread in monocots, although absent in the largest
family – Orchidaceae (Figs. 7 and 8a) [14, 99, 113, 124–127]. They rarely occur
outside monocots and are a result of incomplete fusion of a small region of the carpel
margins [9, 14, 99]. Perigonal nectaries are second-most common type of nectaries
in monocots and may be epidermal as well as trichomatous [99]. Some authors
suggest that perigonal nectaries may have evolved from septal nectaries by
heterochrony, but further studies are necessary to confirm this hypothesis [14,
128–130]. The absence of the septal nectaries or the emergence of perigonal and
staminal nectaries are related to alternative pollination modes (e.g., buzz pollination
in some Asparagales) and attraction (e.g., floral deceit in Dioscoreales) [14, 99,
128–130].
Receptacular nectaries first emerged in the early divergent eudicots. However,
nectaries on petals, staminodes, and carpels also occur in this lineage (Fig. 7) [14,
105]. Within the order Ranunculales, nectar spurs are very noticeable; these are
extensions of various parts of a flower that produce and store nectar (Fig. 8b–c) [14].
In Delphinieae (Ranunculaceae), for example, the nectar spur is formed by
the postgenital fusion of two primordia of the internal perianth whorl and is linked
to the pollinator’s proboscis length [131]. Therefore, morphological variation of
these structures is highly correlated with the type of pollinators and the reproductive
success of individual plants [132].
Distinct receptacular nectaries are common in the core eudicots (Figs. 7 and 8d),
but in flowers with inferior ovary or narrow corolla tubes, they seem to become lost
in the course of evolution [105]. The presentation of nectar through these structures
has many advantages, like the increase of the nectar volume and its constant
production during anthesis, improving the attraction of pollinators [105]. Developmental studies have demonstrated that CRC (crabs claw) expression is required for
nectary development in core eudicots [133] (Fig. 7). This gene is linked to the
regulation of carpel development in early lineages of plants, but its expression in
nectaries of derived lineages suggests a tendency of change from the typically
peripheral perianth position of the nectary in basal taxa to central positions associated with reproductive organs in eudicots [133].
3
Osmophores
The presence of odor is related to the production of volatile oils by secretory
structures located inside or on the surface of vegetative and/or reproductive
organs [134]. In some plants such as Ceropegia (Apocynaceae), Aristolochia
(Aristolochiaceae), and species of Orchidaceae and Araceae, the odor production
is restricted to certain areas of the floral organs, where the cells generally differ
structurally from their neighbors.
28 Diversity of Floral Glands and Their Secretions in Pollinator Attraction
721