been reported from floral structures. While some inflorescences and flowers do
produce resins, they are not necessarily involved in the pollination process. Resin
glands serving in support of pollination are found only in a few genera from different
lineages of plants, such as Clusia and Chrysochlamys of Clusiaceae, Clusiella of
Calophyllaceae, and Dalechampia of Euphorbiaceae [270–272]. Here the resins are
nonnutritive rewards for certain groups of solitary bees that use them to build their
nests [217, 273, 274]. In addition to the structural function, these resins are waterproofing and have antimicrobial, antifungal, and antiviral properties that reduce the
risk of pathogens in nests and thus may help to protect bee larvae [270, 273, 275].
5.2
Resin Glands
The structure of resin glands varies greatly between genera and even among species
of the same genus. In Dalechampia (Euphorbiaceae), for example, parts of the bracts
of the staminate inflorescence are modified in secretory structures, forming a resinsecreting gland [270]. These resin glands are laminar structures that have a palisade
uniseriate epidermis, covered by a cuticle, and responsible for resin secretion in the
inflorescence throughout the development of the pseudanthium [276, 277]. Unlike in
Dalechampia, the floral resin in Clusia (Clusiaceae) is produced and stored in great
quantity in secretory ducts, which exist in all vegetative and reproductive parts of the
plants. Flowers with floral resin glands are marked by secretory resin ducts that are
distributed abundantly on filaments and connectives. These resin ducts are either
simple or branched, and some anatomical studies of Clusia have revealed that the
terminal staminal ducts are externally covered by a single layer of epidermis, which
breaks down during anthesis, releasing the resin on the surface of the filaments [278].
Rupture points on the connective surface associated with the subepidermal resin
ducts were also observed in some species of Clusia [279, 280]. This is understood to
be a very particular and complex case of a floral resin gland, since the resin is
produced and stored in internal secretory structures and posteriorly released to the
external surface during anthesis. In some Clusia species (such as C. insignis and C.
lanceolata), the release of resin above staminodes, in female and some male flowers,
prevents the mixing of pollen with resin, while the opposite occurs in those species
that release the resin above the stamens (such as C. burchellii and C. nigrolineata)
[281] (Fig. 17a–d). These slight differences and the role of the resin in the transfer of
pollen from one flower to another are still under investigation.
Resin glands like those present in flowers of Clusia were also found in the spathe
of Philodendron (Araceae) [13]. In this case, the secretory ducts form a complex
anastomosed system, and the cells of the epithelium separate at the ends of the ducts,
allowing the resin to leak out and accumulate inside intercellular spaces below the
epidermis [13]. The release of the resin is by either rupture of the epidermis covering
the duct or from stomata that coincide at the end of the duct. Although present in the
inflorescence, the resin secretion is not related to the attraction of pollinators (here,
scarab beetles); the resin is crucial for the pollination process, however, since it helps
in the adhesion of the pollen grains to the body of the beetles [282, 283].
736
E. D. Tölke et al.
produce resins, they are not necessarily involved in the pollination process. Resin
glands serving in support of pollination are found only in a few genera from different
lineages of plants, such as Clusia and Chrysochlamys of Clusiaceae, Clusiella of
Calophyllaceae, and Dalechampia of Euphorbiaceae [270–272]. Here the resins are
nonnutritive rewards for certain groups of solitary bees that use them to build their
nests [217, 273, 274]. In addition to the structural function, these resins are waterproofing and have antimicrobial, antifungal, and antiviral properties that reduce the
risk of pathogens in nests and thus may help to protect bee larvae [270, 273, 275].
5.2
Resin Glands
The structure of resin glands varies greatly between genera and even among species
of the same genus. In Dalechampia (Euphorbiaceae), for example, parts of the bracts
of the staminate inflorescence are modified in secretory structures, forming a resinsecreting gland [270]. These resin glands are laminar structures that have a palisade
uniseriate epidermis, covered by a cuticle, and responsible for resin secretion in the
inflorescence throughout the development of the pseudanthium [276, 277]. Unlike in
Dalechampia, the floral resin in Clusia (Clusiaceae) is produced and stored in great
quantity in secretory ducts, which exist in all vegetative and reproductive parts of the
plants. Flowers with floral resin glands are marked by secretory resin ducts that are
distributed abundantly on filaments and connectives. These resin ducts are either
simple or branched, and some anatomical studies of Clusia have revealed that the
terminal staminal ducts are externally covered by a single layer of epidermis, which
breaks down during anthesis, releasing the resin on the surface of the filaments [278].
Rupture points on the connective surface associated with the subepidermal resin
ducts were also observed in some species of Clusia [279, 280]. This is understood to
be a very particular and complex case of a floral resin gland, since the resin is
produced and stored in internal secretory structures and posteriorly released to the
external surface during anthesis. In some Clusia species (such as C. insignis and C.
lanceolata), the release of resin above staminodes, in female and some male flowers,
prevents the mixing of pollen with resin, while the opposite occurs in those species
that release the resin above the stamens (such as C. burchellii and C. nigrolineata)
[281] (Fig. 17a–d). These slight differences and the role of the resin in the transfer of
pollen from one flower to another are still under investigation.
Resin glands like those present in flowers of Clusia were also found in the spathe
of Philodendron (Araceae) [13]. In this case, the secretory ducts form a complex
anastomosed system, and the cells of the epithelium separate at the ends of the ducts,
allowing the resin to leak out and accumulate inside intercellular spaces below the
epidermis [13]. The release of the resin is by either rupture of the epidermis covering
the duct or from stomata that coincide at the end of the duct. Although present in the
inflorescence, the resin secretion is not related to the attraction of pollinators (here,
scarab beetles); the resin is crucial for the pollination process, however, since it helps
in the adhesion of the pollen grains to the body of the beetles [282, 283].
736
E. D. Tölke et al.