Types Of Nectaries Research Articles

Evolution of the floral nectaries in the Primulaceae sensus lato (Ericales)

Abstract The Primuloid clade or Primulaceae sensus lato is well supported and contains several pollination syndromes, including wind pollination and insect pollination with pollen, nectar, or oil as a reward. Previous studies have recognized two types of nectaries (floral and extrafloral) with different distributions (e.g. ovary, stigma, style, pedicel). This study aimed to reassess the diversity of nectary types, and their distribution and evolution within the clade. Flowers were selected to represent the four subfamilies Maesoideae, Theophrastoideae, Primuloideae, and Myrsinoideae. The flowers were investigated for nectary tissue with electron microscopy, light microscopy, and sugar tests. Nectar is mainly exuded by gynoecial nectarostomata (in Maeseoideae, Theophrastoideae, Primuloideae, and a few basal Myrsinoideae, such as Stimpsonia and Coris) distributed at the base, middle, and top part of the ovary. Myrsinoideae is the exception with an absence of a nectary linked to buzz-pollination, or presenting nectariferous or oil-producing trichomes on the perianth and stamens. The evolution of nectaries is variable in the Primuloid clade, with Primuloideae apparently the starting point of an evolutionary reversal in terms of nectary evolution within this clade, and a high diversity of nectaries within the Myrsinoideae representing various trends that are currently under-investigated. The evolution of floral nectaries in Primulaceae presents an exciting shift from nectar-producing flowers towards a loss of nectaries, and an evolutionary reversal with a shift to the co-option of either oil-producing trichomes or nectar-producing trichomes.

Phylotranscriptomics of Swertiinae (Gentianaceae) reveals that key floral traits are not phylogenetically correlated.

Establishing how lineages with similar traits are phylogenetically related remains critical for understanding the origin of biodiversity on Earth. Floral traits in plants are widely used to explore phylogenetic relationships and to delineate taxonomic groups. The subtribe Swertiinae (Gentianaceae) comprises more than 350 species with high floral diversity ranging from rotate to tubular corollas and possessing diverse nectaries. Here we performed phylogenetic analysis of 60 species from all 15 genera of the subtribe Swertiinae sensu Ho and Liu, representing the range of floral diversity, using data from the nuclear and plastid genomes. Extensive topological conflicts were present between the nuclear and plastome trees. Three of the 15 genera represented by multiple species are polyphyletic in both trees. Key floral traits including corolla type, absence or presence of lobe scales, nectary type, nectary position, and stigma type are randomly distributed in the nuclear and plastome trees without phylogenetic correlation. We also revealed the likely ancient hybrid origin of one large clade comprising 10 genera with diverse floral traits. These results highlight the complex evolutionary history of this subtribe. The phylogenies constructed here provide a basic framework for further exploring the ecological and genetic mechanisms underlying both species diversification and floral diversity.

To each their own! Nectar plasticity within a flower mediates distinct ecological interactions.

Nuptial and extranuptial nectaries are involved in interactions with different animal functional groups. Nectar traits involved in pollination mutualisms are well known. However, we know little about those traits involved in other mutualisms, such as ant-plant interactions, especially when both types of nectaries are in the same plant organ, the flower. Here we investigated if when two types of nectaries are exploited by distinct functional groups of floral visitors, even being within the same plant organ, the nectar secreted presents distinct features that fit animal requirements. We compared nectar secretion dynamics, floral visitors and nectar chemical composition of both nuptial and extranuptial nectaries in natural populations of the liana Amphilophium mansoanum (Bignoniaceae). For that we characterized nectar sugar, amino acid and specialized metabolite composition by high-performance liquid chromatography. Nuptial nectaries were visited by three medium- and large-sized bee species and extranuptial nectaries were visited mainly by ants, but also by cockroaches, wasps and flies. Nuptial and extranuptial nectar differed regarding volume, concentration, milligrams of sugars per flower and secretion dynamics. Nuptial nectar was sucrose-dominated, with high amounts of γ-aminobutyric acid and β-aminobutyric acid and with theophylline-like alkaloid, which were all exclusive of nuptial nectar. Whereas extranuptial nectar was hexose-rich, had a richer and less variable amino acid chemical profile, with high amounts of serine and alanine amino acids and with higher amounts of the specialized metabolite tyramine. The nectar traits from nuptial and extranuptial nectaries differ in energy amount and nutritional value, as well as in neuroactive specialized metabolites. These differences seem to match floral visitors' requirements, since they exclusively consume one of the two nectar types and may be exerting selective pressures on the composition of the respective resources of interest.

The structural diversity of floral nectaries does not mean ontogenic diversity in Rhamnaceae species

Rhamnaceae is a family with small, radially symmetrical flowers, which present nectaries of diverse morphology. Therefore, studies to explain the developmental pathways of this diversity are welcome in understanding the evolutionary biology of this gland. Thus, the objective of the present study was to compare the developing floral nectary of six species of Rhamnaceae belonging to different tribes to check its ontogeny and improve the descriptions of nectary types. Buds and flowers were collected and processed for surface, histological and ultrastructural analyses. The nectaries originate from the hypanthium soon after the gynoecium primordium and are generally positioned above the ovary. All nectaries are structured and vary in terms of surface, shape, and presence of indumentum. Two types of nectary were identified: annular and adpressed. The intensity of intercalary growth in the intrastaminal area has a fundamental role in the hypanthium development and consequently, in the differentiation of nectary types. This phenomenon is also responsible for the different positions of annular and adpressed nectaries in flowers of the Rhamnaceae species studied. We conclude that the origin of nectaries in Rhamnaceae seems to be homologous, despite of their great morphological diversity. Also, this study was successful in testing the value of previous nectary classification, placing the investigated species in the categories already defined for the family.

Evolutionary trends and diversity of major floral nectary types across Solanaceae.

In a co-evolutionary crosstalk amid plants and their pollinators, nectaries serve as a labile link between the relatively fixed structural domains of divergent flower forms and associated pollination syndromes. Floral nectary plays a crucial role in sexual plant reproduction by enabling interaction between plants and their pollinators. It is known to associate with different floral whorls, and exhibits variations in structure and location in different clades across angiosperms. To infer evolutionary patterns, it is important to map key features associated with the trait at various taxonomic ranks. In the present study, we analysed variability and distribution of floral nectaries in Solanaceae for the first time. Floral nectaries of 23 taxa representing different clades in the family were studied using bright-field and scanning electron microscopy. The study reveals that although floral nectaries share anatomical similarity, they differ in morphology, composition within cells, and locations within a flower across the clades. The analysis suggests that (i) there is a shift from symmetric, lobed type nectary in the early branching sub-families to asymmetric, annular type in the late branching ones, (ii) floral organization has shifted from asymmetry (zygomorphy) to symmetry (actinomorphy) in corolla, and (iii) the lobed nectary correlates with zygomorphic floral forms that are pollinated by birds and long-tongued vectors, while the annular nectary is predominant among species with bee-pollinated actinomorphic flowers.

Nectar biosynthesis is conserved among floral and extrafloral nectaries.

Nectar is a primary reward mediating plant–animal mutualisms to improve plant fitness and reproductive success. Four distinct trichomatic nectaries develop in cotton (Gossypium hirsutum), one floral and three extrafloral, and the nectars they secrete serve different purposes. Floral nectar attracts bees for promoting pollination, while extrafloral nectar attracts predatory insects as a means of indirect protection from herbivores. Cotton therefore provides an ideal system for contrasting mechanisms of nectar production and nectar composition between different nectary types. Here, we report the transcriptome and ultrastructure of the four cotton nectary types throughout development and compare these with the metabolomes of secreted nectars. Integration of these datasets supports specialization among nectary types to fulfill their ecological niche, while conserving parallel coordination of the merocrine-based and eccrine-based models of nectar biosynthesis. Nectary ultrastructures indicate an abundance of rough endoplasmic reticulum positioned parallel to the cell walls and a profusion of vesicles fusing to the plasma membranes, supporting the merocrine model of nectar biosynthesis. The eccrine-based model of nectar biosynthesis is supported by global transcriptomics data, which indicate a progression from starch biosynthesis to starch degradation and sucrose biosynthesis and secretion. Moreover, our nectary global transcriptomics data provide evidence for novel metabolic processes supporting de novo biosynthesis of amino acids secreted in trace quantities in nectars. Collectively, these data demonstrate the conservation of nectar-producing models among trichomatic and extrafloral nectaries.

A Study on Cotton (Gossypium sp.) Nectar Production in Uzbekistan

Given the importance of cotton varieties in beekeeping, we have been able to determine the nectar and honey yield per hectare for several years Cotton nectaries produce highly concentrated carbohydrates, nectarines, amino acids and fatty acids. Unlike other types of plants. In different varieties of cotton, there are 4 types of nectaries (intra-cup, bract, sub-bract, and leaf), and the number and concentration of nectarium are different for all types. Nectar productivity of fine fiber varieties is significantly higher than that of medium fiber varieties. Nectar is an important nutrient source for insects and pathogens due to its high sugar content. Several methods of nectar determination were used to determine the number of angles of cotton varieties planted in the country, such as "tube" and "washing." On average, honey yield of these varieties is 50-60 kg per hectare. It is understood from the research results that cotton varieties have high honey and nectar productivity in Uzbekistan environment.

Floral anatomy of Tristerix longebracteatus (Loranthaceae)

Introduction: Most of the New World members of the Loranthaceae comprise a clade that corresponds to the tribe Psittacantheae. Previous studies on floral anatomy and development in this tribe have concentrated on the highly diversified subtribe Psittacanthinae, while the smaller subtribe Ligarineae has received less attention. A detailed anatomical description of Tristerix longebracteatus helps to fill this information gap. Objetive: The present research analyzes the anatomy of Tristerix longebracteatus flowers, detailing the structure of androecium and gynoecium, including megasporogenesis and microsporogenesis. Methodology: Anatomical serial sections of flowers at different stages of development were prepared, following processing with fixation techniques, incorporation in paraffin, microtome sectioning and staining with Astra-blue and basic fuchsin. Results: The large-sized flowers of Tristerix longebracteatus present a complex pattern of vascularization with 18-20 vascular bundles at the base of the inferior ovary. A group of three vascular bundles irrigate the 4-5 petals and associated stamens, and ten bundles continue through the gynoecium. The androecium is composed of four or five anthers with simultaneous microsporogenesis. The gynoecium as a single ovarian cavity with a central mamelon in which the archesporial tissue is oriented towards the style. The base of the style forms a nectary similar to that found in the sister genus Ligaria. Conclusions: The gynoecium with a single ovarian cavity and central mamelon is a condition shared by Tristerix (subtribe Ligarinae) and all the genera of the subtribe Psittacanthinae, except Tripodanthus. The base of the style forms a nectary similar to that found in the sister genus Ligaria. This type of stylar nectary is of taxonomic value for grouping species of the subtribe Ligarinae and difers from the annular nectary of subtribe Psittacanthinae.

Extrafloral nectary-bearing plant Mallotus japonicus uses different types of extrafloral nectaries to establish effective defense by ants

Extrafloral nectary (EFN)-bearing plants attract ants to gain protection against herbivores. Some EFN-bearing plants possess different types of EFNs, which might have different effects on ants on the plants. Mallotus japonicus (Thunb.) Muell. Arg. (Euphorbiaceae) bears two types of EFNs, including a pair of large EFNs at the leaf base and many small EFNs along the leaf edge. This study aimed to determine the different roles of the two types of EFNs in biotic defense by ants. A field experiment was conducted to investigate the effect of leaf damage on EFN production and on the distribution pattern of ants. After leaf damage, the number of leaf edge EFNs increased in the leaves first-produced. The number of ants on the leaves also increased, and the foraging area of ants extended from the leaf base to the leaf tip. An EFN-covering field experiment revealed that leaf edge EFNs had a greater effect than leaf base EFNs on ant dispersal on leaves. The extended foraging area of ants resulted in an increase of encounter or attack rate against an experimentally placed herbivore, Spodoptera litura. These results suggest that M. japonicus plants control the foraging area of ants on their leaves using different types of EFNs in response to leaf damage, thus achieving a very effective biotic defense against herbivores by ants.

Diversity of floral nectary secretions and structure, and implications for their evolution in Anacardiaceae

The flowers of most Anacardiaceae have a floral nectary disk producing nectar rich in sugars. However, a recent study demonstrated that their nectaries might also produce other substances, including lipids and phenolic compounds. To explore the diversity of floral nectary production and (ultra)structure, and their potential for the systematics of Anacardiaceae, we studied seven genera and 13 species from the two subfamilies. We used spectrophotometry to identify sugars and histochemical tests for other substances, and electron and brightfield microscopy to study nectary (ultra)structure and secretory pathways. The composition of sugars and other substances can vary between closely related species and be more similar in species from different subfamilies, being of limited value for the systematics of the family. The general morphology and structure of the floral nectary and their secretory pathways appear to be conservative in the family, and, like the production of mixed secretions, they might be plesiomorphic. Three morphological types of floral nectaries are defined for the family: nectariferous disk with papillose (1) or smooth epidermis-type (2) and trichomatous-type (3). The secretions may be released both by granulocrine and eccrine mechanisms and exuded through nectarostomata or the cuticle. Further studies are needed to better understand their evolutionary and ecological implications in Anacardiaceae and other sapindalean lineages.

Morphological study of floral nectaries in Euonymus and the probable origin of the echinate fruit surface

A conspicuous nectary disk is common but has a distinguishing morphology in the cosmopolitan genus Euonymus. Our study focuses on the morphology of floral nectaries in 21 representatives of Euonymus and Glyptopetalum. Two main types of nectaries were documented: a mix of inter- and extrastaminal nectaries existed between the corolla and the stigma, while the intrastaminal nectaries were distributed between the stigma and the stamen bases. The main route of nectar release in Euonymus is via modified stomata, and different nectarostomata locations were observed: in depressions, slightly raised above the epidermal surface or at the same level as the epidermis. Floral nectaries in E. sect. Echinococcus species developed into the protrusions on the fruit surface at the later stage. The development of nectaries not only explained the mystery of the origin of the echinate fruit surface, but also showed that differences in fruit surface might be inappropriate for use in infrageneric classification. These discoveries inform morphological observations of floral nectaries in Euonymus.

Morphological and ultrastructural studies of floral nectaries in Rhamnaceae

Morphology, anatomy, and ultrastructure of nectaries of 12 species belonging to five tribes of Rhamnaceae (Pomaderreae, Colletieae, Paliureae, and Gouanieae of the Ziziphoids clade and Rhamneae of the Rhamnoids clade) were studied by light and electron microscopy. Four types of nectaries were observed in this study. Species of the tribes Rhamneae, Gouanieae, Paliureae, and Cryptandra tomentosa Lindl. of the Pomaderreae tribe have annular nectaries. Siegfriedia darwinioides C.A. Gardner and Stenanthemum humile Benth. (Pomaderreae) have revolute nectaries, as do Colletia paradoxa (Spreng.) Escalante and Colletia spinosissima J.F. Gmel. (Colletieae). Retanilla patagonica (Speg.) Tortosa and Kentrothamnus weddellianus (Miers) M.C. Johnst. (Colletieae) have indistinct and adpressed nectaries, respectively. Nectar secretion occurs through modified nectary stomata in all species. Differences in the ultrastructure, mode of nectar secretion, and position of the nectaries are discussed. According to the organelles found in the nectary cells of all the species studied, granulocrine secretion is most likely to occur. Further research on these structures in additional species of this family could help to establish nectary homologies.

Nectaries in fly-deceptive pitcher-trap blossoms of Aristolochia

The flowers of the eight Aristolochia species studied in this paper (A. arborea, A. clematitis, A. gigantea, A. grandiflora, A. rotunda, A. salvadorensis, A. sempervirens, A. tricaudata) represent three different pollinator deceit cases in this genus: brood site mimic in carrion-fly and fungus-gnat blossoms and food source mimic. In any case, all of them have nectaries on the inner wall of the kettle which provide a small quantity of nectar. As regards the histology, two different types of nectaries can be discerned: the trichomatous type and the so-called nectarioles (termed by Vogel, 1998). The latter type, characterized by clusters of independent and isolated glandular units, is reported for the first time in the kettles of Aristolochia, namely in A. arborea, A. salvadorensis and A. tricaudata.The nectar production in the kettles of the investigated species is regarded as food ensuring survival of the imprisoned pollinators during captivity. Additionally, the location of the nectaries on the inner kettle wall can be interpreted as an adaptation directing the trapped flies to the exit after pollination and fresh pollen loading.

Floral structure in the Asian palm Eugeissona tristis Griff. (Arecaceae: Calamoideae), and description of a new nectary type in the family

The South-East Asian palm genus Eugeissona has an unusual flower structure, and it occupies a basal position in the early divergent palm subfamily Calamoideae. This article describes the floral structure of Eugeissonatristis, a palm that has been associated with an uncommon pollination syndrome in which non-flying mammals ingest large amounts of fermenting nectar produced by flowers. Our study focuses on the architecture of the nectaries responsible for this nectar production. The nectariferous tissues differentiate in four histological regions along the length of the gynoecium, and appear to be primarily associated with ventral slits of the carpels, corresponding to pollen tube transmitting tracts (PTTT). Nectariferous tissues also develop along the carpel septa—as is typical for the Monocotyledons—but to a much lesser extent. A comprehensive review of the nectariferous systems diversity in palms confirms that it represents an undescribed type of nectary unique to the family, and demonstrates a topographical shift when compared to the septal or labyrinthine types typical of other palms. The non-flying mammal pollination syndrome observed in Eugeissona tristis is described and compared with similar syndromes in other angiosperms.

Floral nectar production and carbohydrate composition and the structure of receptacular nectaries in the invasive plant Bunias orientalis L. (Brassicaceae)

The data relating to the nectaries and nectar secretion in invasive Brassicacean taxa are scarce. In the present paper, the nectar production and nectar carbohydrate composition as well as the morphology, anatomy and ultrastructure of the floral nectaries in Bunias orientalis were investigated. Nectary glands were examined using light, fluorescence, scanning electron and transmission electron microscopy. The quantities of nectar produced by flowers and total sugar mass in nectar were relatively low. Total nectar carbohydrate production per 10 flowers averaged 0.3 mg. Nectar contained exclusively glucose (G) and fructose (F) with overall G/F ratio greater than 1. The flowers of B. orientalis have four nectaries placed at the base of the ovary. The nectarium is intermediate between two nectary types: the lateral and median nectary type (lateral and median glands stay separated) and the annular nectary type (both nectaries are united into one). Both pairs of glands represent photosynthetic type and consist of epidermis and glandular tissue. However, they differ in their shape, size, secretory activity, dimensions of epidermal and parenchyma cells, thickness of secretory parenchyma, phloem supply, presence of modified stomata and cuticle ornamentation. The cells of nectaries contain dense cytoplasm, plastids with starch grains and numerous mitochondria. Companion cells of phloem lack cell wall ingrowths. The ultrastructure of secretory cells indicates an eccrine mechanism of secretion. Nectar is exuded throughout modified stomata.

Floral nectary morphology and evolution inPedicularis(Orobanchaceae)

Intricate associations between floral morphology and pollinator foraging behaviour are common. In this context, the presence and form of floral nectaries can play a crucial role in driving floral evolution and diversity in flowering plants. However, the reconstruction of the ancestral state of nectary form is often hampered by a lack of anatomical studies and well-resolved phylogenetic trees. Here, we studied 39 differentially pollinated Pedicularis spp., a genus with pronounced interspecific variation in colour, shape and size of the corolla. Anatomical and scanning electron microscopy observations revealed two nectary forms [bulged (N=27) or elongated (N=5)] or the absence of nectaries (N=7). In a phylogenetic context, our data suggest that: (1) the bulged nectary should be the ancestral state; (2) nectaries were independently lost in some beaked species; and (3) elongated nectaries evolved independently in some clades of beakless species. Phylogenetic path analysis showed that nectary presence is indirectly correlated with beak length/pollinator behaviour through an intermediate factor, nectar production. No significant correlation was found between nectary type and nectar production, beak length or pollinator behaviour. Some beaked species had nectary structures, although they did not produce nectar. The nectary in beaked species may be a vestigial structure retained during a recent rapid radiation of Pedicularis, especially in the Himalaya-Hengduan Mountains of south-western China.(c) 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 178, 592-607.

CODONOBOEA (GESNERIACEAE) SECTIONS IN PENINSULAR MALAYSIA

Codonoboea is the largest genus of Gesneriaceae in Peninsular Malaysia with 92 species. Nine sections, Boeopsis, Codonoboea, Didymanthus, Glossadenia, Heteroboea, Pectinati, Reptantes, Salicini and Venusti, have been erected based on morphological characters, such as habit, leaf arrangement and shape, type of inflorescence, number of flowers, corolla type and nectary type. Recent molecular phylogenetic study using ITS and trnL-F sequences show that only section Heteroboea is monophyletic. While the sections of Codonoboea can no longer be maintained as formal taxonomic taxa, as informal groupings they are useful in identification and in constructing keys.

Plant size and reproductive state affect the quantity and quality of rewards to animal mutualists

Summary Many plants engage ants in defensive mutualisms by offering extrafloral nectar (EFN). Identifying sources of variation in EFN quantity (amount) and quality (composition) is important because they can affect ant visitation and identity and hence effectiveness of plant defence. I investigated plant size and reproductive state (vegetative or flowering) as sources of variation in EFN quantity and quality. I focused on Opuntia imbricata and two ant partners, Crematogaster opuntiae and Liometopum apiculatum. I tested the influence of plant size and nectary type (vegetative vs. reproductive structure) on the probability and rate of EFN secretion, concentrations of total carbohydrates (CH) and amino acids (AAs), and relative abundances of constituent CH and AAs. I also examined how traits of individual nectaries scaled up to influence total plant‐level rewards. Parallel observations documented associations between plant demographic state and ant visitation and species identity. EFN quantity and quality were generally greater for larger, reproductive plants. At the scale of individual nectaries, probability of EFN secretion was positively size‐dependent and greater for nectaries on reproductive vs. vegetative structures. Rate of EFN secretion, carbohydrate and amino acid concentrations, and the relative abundance of disaccharide vs. monosaccharide sugars were greater for reproductive nectaries but were unaffected by plant size. Nectary‐level traits scaled up to influence rewards at the whole‐plant level in ways that corresponded to ant visitation: the probability of ant occupancy increased with plant size and reproduction, as did the likelihood of being tended by the superior guard, L. apiculatum. Variability in EFN traits may contribute to changes in ant occupancy and identity across plant sizes and reproductive states. Synthesis. This study provides a thorough examination of how plant investment in biotic defence varies over the life cycle. Explicit consideration of plant demography may enhance understanding of ant–plant mutualisms. Populations of long‐lived plants are demographically heterogeneous, spanning sizes and reproductive states. The rewards offered to animal mutualists can track demographic heterogeneity with consequences for plant defence and the dynamics of multispecies mutualisms.

The systematic significance of floral morphology, nectaries, and nectar concentration in epiphytic cacti of tribes Hylocereeae and Rhipsalideae (Cactaceae)

A long-standing interest in cactus taxonomy has existed since the Linnaean generation, but an appreciation of the reproductive biology of cacti started early in the 1900s. Numerous studies indicate that plant reproductive traits provide valuable systematic information. Despite the extensive reproductive versatility and specializations in breeding systems coupled with the striking floral shapes, the reproductive biology of the Cactaceae has been investigated in approximately 10% of its species. Hence, the systematic value of architectural design and organization of internal floral parts has remained virtually unexplored in the family. This study represents the most extensive survey of flower and nectary morphology in the Cactaceae focusing on tribes Hylocereeae and Rhipsalideae (subfamily Cactoideae). Our objectives were (1) to conduct comparative morphological analyses of flowers and floral nectaries and (2) to compare nectar solute concentration in these two tribes consisting of holo- and semi-epiphytic species. Flower morphology, nectary types, and sugar concentration of nectar have strong taxonomic implications at the tribal, generic and specific levels. Foremost, three types of nectaries were found, namely chamber nectary (with the open and diffuse subtypes), furrow nectary (including the holder nectary subtype), and annular nectary. All Hylocereeae species possess chamber nectaries, in which the nectarial tissue has both trichomes and stomata. The Rhipsalideae are distinguished by two kinds of floral nectaries: furrow and annular, both nectary types with stomata only. The annular nectary type characterizes the genus Rhipsalis. Nectar concentration is another significant taxonomic indicator separating the Hylocereeae and Rhipsalideae and establishing trends linked to nectar sugar concentration and amount of nectar production in relation to flower size. There is an inverse relationship between flower size and amount of nectar production in the smaller Rhipsalideae flowers, in which nectar concentration is more than two-fold higher despite the smaller volume of nectar produced when compared to the large Hylocereeae flowers. Variability of nectary morphology and nectar concentration was also evaluated as potential synapomorphic characters in recent phylogenies of these tribes. In conclusion, our data provide strong evidence of the systematic value of floral nectaries and nectar sugar concentration in the Cactaceae, particularly at different taxonomic levels in the Hylocereeae and Rhipsalideae.

The evolution of floral nectaries in Disa (Orchidaceae: Disinae): recapitulation or diversifying innovation?

The Orchidaceae have a history of recurring convergent evolution in floral function as nectar production has evolved repeatedly from an ancestral nectarless state. However, orchids exhibit considerable diversity in nectary type, position and morphology, indicating that this convergence arose from alternative adaptive solutions. Using the genus Disa, this study asks whether repeated evolution of floral nectaries involved recapitulation of the same nectary type or diversifying innovation. Epidermis morphology of closely related nectar-producing and nectarless species is also compared in order to identify histological changes that accompanied the gain or loss of nectar production. The micromorphology of nectaries and positionally equivalent tissues in nectarless species was examined with light and scanning electron microscopy. This information was subjected to phylogenetic analyses to reconstruct nectary evolution and compare characteristics of nectar-producing and nectarless species. Two nectary types evolved in Disa. Nectar exudation by modified stomata in floral spurs evolved twice, whereas exudation by a secretory epidermis evolved six times in different perianth segments. The spur epidermis of nectarless species exhibited considerable micromorphological variation, including strongly textured surfaces and non-secreting stomata in some species. Epidermis morphology of nectar-producing species did not differ consistently from that of rewardless species at the magnifications used in this study, suggesting that transitions from rewardlessness to nectar production are not necessarily accompanied by visible morphological changes but only require sub-cellular modification. Independent nectary evolution in Disa involved both repeated recapitulation of secretory epidermis, which is present in the sister genus Brownleea, and innovation of stomatal nectaries. These contrasting nectary types and positional diversity within types imply weak genetic, developmental or physiological constraints in ancestral, nectarless Disa. Such functional convergence generated by morphologically diverse solutions probably also underlies the extensive diversity of nectary types and positions in the Orchidaceae.