Comparative systematic study of colleters and stipules of Rhizophoraceae with implications for adaptation to challenging environments

Colleters are multicellular secretory structures found on various organs in flowering plants. Colleters on the adaxial sides of stipules have been hypothesized to play a role in protecting the developing shoot. Rhizophoraceae is a stipulate family with a broad distribution from mangrove to montane environments, which makes the family well suited for the examination of this hypothesis, but the colleters of Rhizophoraceae are not well known. We compared species from all three tribes of Rhizophoraceae, including five inland genera and all four mangrove genera. In all species, several to hundreds of colleters, sessile or stalked, arranged in rows aggregated in genus‐specific shapes, are found at the adaxial bases of open and closed stipules. Pellacalyx uniquely has additional colleters at the stipule margins. Colleters are all of the standard type, comprising a central axis of core parenchyma with large vacuoles and tannins, and an outer palisade‐like epidermis with organelles involved in secretory activity. An exception is Pellacalyx axillaris, in which colleters appear as extremely small epidermal protrusions. Kandelia obovata has a tracheary element in some colleters. Pellacalyx uniquely has an unusual fleshy outgrowth on the adaxial stipule base. We propose an evolutionary sequence in which Macarisia has plesiomorphic stipule and colleter traits and the mangrove Kandelia obovata with colleter vascular traces is most derived. Colleter and stipule structures are largely concordant with habitat and phylogeny, and show taxonomic value. The strong alignment of colleter and stipule patterns with habitat is suggestive that colleters have a protective function, although some components of these patterns may be phylogenetically determined. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 172 , 449–464.     

Development, Structure and Cytochemistry of Resin-secreting Colleters of Gardenia gummifera (Rubiaceae)

The structure, ontogeny and cytochemistry of stipular colletersof Gardenia gummifera are described. The repeated division ofa few adaxial protodermal and subprotodermal cells of the youngstipule and the subsequent elongation by the latter resultsin the formation of a standard-type colleter. A developed colleterhas outer palisade-like glandular cells covered by a continuouscuticle and inner layers of elongated columnar cells. Enzymelevels in the palisade-like epidermal cells in the colletersindicate their active role in secretion. The secretion is resinous,occurs in the young colleters, and accumulates between the cellsand the cuticle. The cuticle later ruptures and releases thesecretory product, which drenches the young shoot apex. Gardenia gummifera L, stipule, colleters, resin, ontogeny, cytochemistry     

The structure of colleters in several species of Simira (Rubiaceae)

BACKGROUND AND AIMS: Colleters are secretory structures consisting of a parenchymatic middle axis surrounded by a layer of palisade-like epidermal cells. Colleters occur in a large number of rubiaceous species. Their function is to protect the developing shoot apex. They are also taxonomically useful in the Rubiaceae. This study characterized the structure of the colleters of Simira glaziovii, S. pikia and S. rubra and the biochemistry of secretions in S. glaziovii. METHODS: Stipules of the shoot apices of the three species studied were collected at Barragem de Saracuruna, in Rio de Janeiro state, Brazil. The samples were fixed according to the usual methods for light and electron microscopy. Secretion stipules of S. glaziovii were washed with 0.1 m Tris-HCl plus 0.1 %Triton X-100 to extract proteins and carbohydrates. KEY RESULTS: Colleters in these species are located at the base of the stipule. Each species shows a different pattern of distribution. They form as emergentia from the stipules. Simira glaziovii was different from the other two species because it exhibited vascular traces. The epidermal cells of colleters have dense cytoplasm, nuclei, small vacuoles, endoplasmic reticulum, Golgi apparatus, mitochondria and extraplasmic spaces if they are secretory. The outer cell wall of the mature colleters differs from the outer cell wall of stipule cells and immature colleters. Both carbohydrates and proteins were found in secretions from the stipules of S. glaziovii. CONCLUSIONS: Few ultrastructural differences were noted among the three species. These secretory structures not only protect the shoot apex, but also have taxonomic importance below the genus level.     

Colleter morphology in Pavetta, Neorosea and Tricalysia (Rubiaceae) and its relationship to the bacterial leaf nodule symbiosis

Buds removed from herbarium specimens were processed for light microscopic examination of colleter form and anatomy. Most Pavetta species have dendroid colleters and bacterial leaf nodules, a correlation also found in an earlier study of Psychotria. Colleters of Neorosea , another genus with leaf-nodulated species, are more like the standard rubiaceous type that predominates in the family except that they have irregular, bulging epidermal cells. Tricalysia , a nodule-free genus closely related to Neorosea , shows a range of colleter form from standard to dendroid, and some species have the Neorosea type of colleter. Such morphological correlation between the bacterial leaf nodule symbiosis in Pavetta and Psychotria and dendroid colleters may indicate a chemical change in colleter secretion. Apart from their involvement with the bacterial symbiosis, rubiaceous colleters have now been shown to vary sufficiently in certain taxa to be considered as additional useful taxonomic characters.     

Colleters in Turnera and Piriqueta (Turneraceae)

The anatomy of colleters was examined by light and scanning electron microscopy in 25 species of Turnera and nine species of Piriqueta. Based on morphology, four categories of colleters were recognized: standard, sessile, lachrymiform and trochleariform, all of which differ in shape and length/width ratio. They all have a similar anatomy: they consist of an axis of parenchymatous cells, sheathed by a palisade epidermis. The standard type is the most widespread in the studied taxa; the lachrymiform example was found in those species of Piriqueta with setiform glandular hairs; only one trochleariform example appeared in T: diffusa. The sessile type is considered to be a morphological transitional form between extrafloral nectaries and colleters. This is the first record of sessile, lachrymiform and trochleariform colleters. The anatomy of colleters is compared with other secretory structures such as glandular trichomes and extrafloral nectaries.     

Colleter types in Rubiaceae, especially in relation to the bacterial leaf nodule symbiosis

Vegetative buds were removed from herbarium specimens, and a small number of living plants, of 116 species of 111 genera of Rubiaceae and processed for light-microscopic examination of colleter form and anatomy. The results were combined with those of earlier studies. Most colleters in this family are of the 'standard type' described by others. Colleters are, however, lacking in eight genera. dendroid colleters occur in six genera. Two other genera have an intermediate type of colleter. Three genera have bacterial leaf nodules; dendroid colleters are not restricted to these genera, but their pattern of occurrence suggests a causal relationship between bacterial infection and evolution of dendroid colleters. Coupled with the geographic distribution of nodulared species within these genera, this pattern indicates that Pavetta became infected very early in its evolutionary history, Psychotria relatively later, and Neorosea most recently.     

Leaf colleters in Tontelea micrantha (Celastraceae,Salacioideae): Ecological,morphological and structural aspects

The colleter secretion can be useful to protect plants of Cerrado (Brazilian savanna) biome during the long and pronounced dry season. This study describes the presence of colleters in Tontelea micrantha and represents the first record of these structures in Celastraceae. To investigate colleter structure and their secretory processes, young leaves were collected, fixed, and processed according to conventional techniques for light, and electron microscopy. Colleters were observed at the marginal teeth on the leaf. They produce mucilaginous secretions that spread over the leaf surface. After secretory phase, colleters abscise. The secretory epithelium is uniseriate and composed of elongated cells whose dense cytoplasm is rich in organelles. The ultrastructure of the secretory cells is compatible with the pectin-rich secretion. Observations of the young leaves surface revealed the presence of superficial hydrophilic secretion films that appeared to have the function of maintaining the water status of those organs.     

New information for Ilex phylogenetics based on the plastid psbA‐trnH intergenic spacer (Aquifoliaceae)

The aim of the present work was to clarify the origin and phylogenetic position of the species belonging to the genus Ilex (Aquifoliaceae), especially the South American species. Phylogenetic relationships of the genus Ilex were investigated using the plastid psbA‐trnH intergenic spacer and parsimony and Bayesian analyses. The psbA‐trnH intergenic spacer was shown to evolve slowly within Ilex, but a major gap present in this region was useful in the phylogenetic study of the genus. To obtain more potentially parsimonious characters, atpB‐rbcL intergenic spacer data were combined with those for psbA‐trnH. Many gaps present in the psbA‐trnH region were useful in the phylogenetic study of the genus Ilex. The topology of the trees showed that, in general, the clades are strongly related to geographical areas, a fact especially evident in certain different Asian lineages. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 182–193.     

Two new species from Gabon show the need to reduce Commitheca to the synonymy of Pauridiantha (Rubiaceae, Pauridiantheae)

Two new Pauridiantha species (Pauridiantheae, Rubiaceae) from Gabon are described and illustrated. Pauridiantha pleiantha is characterized by a combination of entirely glabrous stems, stipules with a narrow base, and large inflorescences. Pauridiantha smetsiana is characterized by entirely glabrous stems, narrow, early deciduous stipules, leaves red-tinged when dry, and small inflorescences. The two new species, especially P. smetsiana , close the morphological gap between Commitheca and Pauridiantha in combining typical Commitheca characters, such as glabrous stems and a narrow stipular base, with Pauridiantha characters, such as eucamptodromous venation. A detailed morphological comparison (including ovary structure, seed morphology, exotesta anatomy, and pollen morphology) between the two genera is given; in conclusion, Commitheca is relegated to the synonymy of Pauridiantha . The necessary new specific combinations are provided.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 141 , 105–117.     

MORPHOLOGY AND DISTRIBUTION OF COLLETERS AND CRYSTALS IN RELATION TO THE TAXONOMY AND BACTERIAL LEAF NODULE SYMBIOSIS OF PSYCHOTRIA (RUBIACEAE)

Earlier investigators established that a finger-like colleter with elongate axial cells and a palisade epidermis is the standard type in the Rubiaceae. This type, with some variation, also prevails in Psychotria, based on a worldwide anatomical survey of vegetative buds from herbarium specimens of 296 species (about 50 % of total). It is virtually the only type found outside of continental Africa. Among African species, it is most common in subgenus Psychotria, with mostly nodule-free species. In subgenus Tetramerae, with only leaf-nodulated species, there is a strong tendency toward brushlike and dendroid colleters in which epidermal cells are extremely elongate and separated from each other. It is speculated that this change in colleter morphology associated with presence of nodule bacteria may be correlated with a change in secretion product more suitable for support of bacteria. Three morphological forms of crystal occur: raphides, styloids, clustered crystals. They may occur singly or in combination. Several patterns and trends were noted in crystal distribution that could be of taxonomic significance.     

Histochemistry and Senescence of Colleters of Allamanda cathartica (Apocynaceae)

Allamanda have colleters on the adaxial bases of petiole, bractsand bracteoles. Each colleter is finger shaped, differentiatedinto a long head on a short stalk. Vasculature to the colleteris absent but branched laticifers are present among the centralcells. Secretion of the colleter contains glucose and rhamnose.The major elements present in the exudate are Na, Fe and Zn.Starch, protein and lipids were identified, with lipids themajor component. Petiolar colleters are persistent and becomestiff due to the lignification occurring in the walls of epithelialand central cells. Because of over-lignification in the centralcells, the cell lumen is highly reduced. Allamanda, colleter, laticifer, secretion, senescence     

Leaf morphology and anatomy of Camellia section Camellia (Theaceae)

The delimitations of species in Camellia section Camellia have been disputed for many years, resulting from uncertain relationships among species. Leaf morphological and anatomical characters for 54 species and three varieties in this section were investigated to reveal the relationships. Principal component analysis and cluster analysis were conducted using the transformed data for quantitative and qualitative characters from leaf morphology and anatomy. Combining the results of statistical analysis with comparative leaf characters of morphology and anatomy, we discussed the taxonomic treatment of section Camellia by Chang compared with that of Ming and we conclude that section Camellia consists of c. 50 species. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 456–476.     

Über die strittige Homologie sogenannter Stipulardrüsen bei einigenEuphorbia-Arten der SektionEuphorbium

Developmental studies of leaf glands in species of sect.Euphorbium Benth. make it doubtful that even the ones in stipular position are truly homologous with stipules.     

Calycine colleters of seven species of Apocynaceae (Apocynoideae) from Brazil

The structure and organization of calycine colleters belonging to four genera of Apocynaceae are described. Calycine colleters were found in all species. All colleters had the same histological composition, but morphological differences were observed in four species. Most colleters were of the standard type, and possible deviations resulted in three morphological types: bifurcated, laminar, and sessile. Mechanisms of cell separation, proliferation, and elongation may explain the origin of the new types. As a consequence of morphological changes, the secretory surface was expanded in the bifurcated, laminar, and sessile glands. Most colleters were in a post-secretory phase, but a hydrophilic secretion was observed in Mandevilla pycnantha and Mesechites mansoana . A larger secretory surface, together with the extension of the secretory phase in adult flowers, were major shifts in the calycine colleters of Apocynaceae, and are possibly correlated with the functional and ecological aspects of these organs. Three patterns of distribution of calycine colleters were observed: alternate, opposite, or indefinitely distributed. The alternate pattern was not homogeneous, and three subtypes were recognized: four-, five-, and ten-grouped colleters. The number of calycine colleters was variable between taxa and even within the same species.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 152 , 387–398.     

Development of leaves and shoot apex protection in Metrodorea and related species (Rutaceae)

Most members of Sapindales are characterized by compound leaves, but several genera also (or only) produce simple or unifoliolate leaves. A few genera may bear stipules or pseudostipules. Little is known about the morphological structure and morphogenesis of these types of leaves in Sapindales, but this information is required for comparative and evolutionary studies. Metrodorea is a Neotropical genus of Rutaceae, comprising species presenting compound and unifoliolate leaves, plus heterophylly, together with an intriguing bud‐protecting structure at the leaf base. The aims of the present study are: (1) to examine leaf morphogenesis in Metrodorea and in closely related species (four Esenbeckia spp., Helietta apiculata and Raulinoa echinata); and (2) to improve our understanding of the morphological evolution of leaves in Metrodorea and Rutaceae. Our data show that the hood‐shaped structure at the base of the leaf in Metrodorea, usually interpreted as a sheath, is, in fact, a pair of united stipules, a synapomorphy of the genus. In the species studied, it is possible to recognize two main types of unifoliolate leaf: early unifoliolate leaves and late unifoliolate leaves. We also found that the number of leaflets in the studied species is dependent on the late or early determination of the leaf primordium, and that loss of leaflets may have been favoured by the restriction of space available for development within the cavity formed by the pair of united stipules. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 178 , 267–282.     

Dendroid colleters on vegetative and reproductive apices in Alibertia sessilis (Rubiaceae) differ in ultrastructure and secretion

In this work we compare the structure and secretion of dendroid colleters on stipules, bracts and sepals of Alibertia sessilis, a non-nodulate Rubiaceae species from Brazilian cerrado, with notes on the plant phenology. Samples were processed according to usual methods for anatomy, histochemistry and ultrastructure. Colleters are conical and constituted by a central axis of elongated parenchyma cells from which radiate numerous epidermal cells. Epidermal cells are cylindrical on the vegetative apex and digitiform or bulbous on reproductive apex. Both colleters produce hydrophilic and lipophilic compounds. On the vegetative apex, epidermal cells present numerous well-developed Golgi bodies associated with a network of smooth endoplasmatic reticulum (SER), scarce oil bodies and profiles of rough endoplasmatic reticulum (RER), indicating the involvement of these glands in the production of mainly polysaccharides in addition to protein and lipids. Differently, epidermal cells on bracts and sepals present abundant and prominent oil drops, fewer Golgi bodies and a well developed network of SER with locally dilated cisterns indicating predominance of lipids. Ecrine and granulocrine mechanisms are common to colleters of both apices. We hypothesize that exudates protect vegetative meristems and developing organs against desiccation in the dry season and against insects and pathogens during the wet season. Predominantly lipidic secretion protects the floral organs against dehydration in the dry season and can attract floral visitants. These aspects are relevant if one considers that A. sessilis inhabits the cerrado, an environment characterized by a well-delimited dry season, high irradiance and elevated vapor pressure deficits.     

Taxonomic revision of the tribe Hymenodictyeae (Rubiaceae, Cinchonoideae)

The palaeotropical tribe Hymenodictyeae Razafim. & B. Bremer, belonging to the otherwise predominantly Neotropical subfamily Cinchonoideae  s.s. (coffee family or Rubiaceae), is revised here. The tribe as presently circumscribed contains two genera, Hymenodictyon Wall. and Paracorynanthe Capuron ex J.-F. Leroy, and is distinct from the other Cinchonoideae tribes with capsular fruits in having stipules bearing large, deciduous colleters on the margins, valvate corolla aestivation, and lenticellate capsular fruits that contain elongate, bilaterally flattened, and accrescent placentae. We recognize 22 Hymenodictyon species, including four new species ( H. antakaranensis sp. nov. , H. epiphyticum sp. nov. , H. madagascaricum sp. nov. , and H. tsingy sp. nov. ), and the two described species of Paracorynanthe . Hymenodictyon is distinguished from its sister genus, Paracorynanthe , by simple or compound spicate, racemose or thyrsoid inflorescences and corolla lobes without any appendages, rather than compound umbelliform inflorescences and corolla lobes prolonged by ciliate appendages. A full taxonomic treatment, keys, and distribution maps of all recognized Hymenodictyon and Paracorynanthe species are provided. Five lectotypes and one neotype are designated. Finally, six Hymenodictyon species are illustrated for the first time.  © 2006 The Linnean Society of London, Botanical Journal of the Linnean Society , 2006, 152 , 331–386.     

Trichome forms in Ardisia (Myrsinaceae) in relation to the bacterial leaf nodule symbiosis

Symbiotic leaf-nodule bacteria in nodulated members of Rubiaceae live in mucilage secreted by colleters located on stipules within buds. These differ from colleters on most nodule-free species. This study was undertaken to examine buds of Ardisia and the related monotypic Amblyanthus of Myrsinaceae to see if nodulated species had secretory structures dissimilar from those of nodule-free species. Buds removed from herbarium specimens (61 species) and live plants (3 species) were paraffin-sectioned. Diverse trichome forms occur, including dimorphism between adaxial and abaxial trichomes in some species. Species within each subgenus were arranged according to trichome form: peltate scale, irregularly capitate, capitate, sessile capitate, bicellular capitate, and uniseriate. Only seven Ardisia species (all in subgenus Crispardisia, widely assumed to have bacteria in marginal leaf nodules of all 30 species) have short-lived trichomes bearing one or more elongate, swollen, distal cells that appear to be secretory cells. These trichomes are analogous to the dendroid or brushlike colleters of nodulated Rubiaceae. Druses occur in most subgenera and this appears to be by far the most predominant crystal type m Ardisia.     

Anatomy and histochemistry of colleters in Roupelia grata (Apocynaceae)

The colleters of Roupelia grata are present on the petiole of the leaf, bract, bracteole and calyx. A mature colleter has a distinct head and a stalk. The parenchymatous central core is surrounded by epithelial cells. The senescence of the colleter occurs at its apex first and then proceeds towards the base.