The relationship between nectaries and floral architecture: a case study in Geraniaceae and Hypseocharitaceae.

Background and Aims: Flowers of Geraniaceae and Hypseocharitaceae are generally considered as morphologically simple. However, previous studies indicated complex diversity in floral architecture including tendencies towards synorganization. Most of the species have nectar-rewarding flowers which makes the nectaries a key component of floral organization and architecture. Here, the development of the floral nectaries is studied and placed into the context of floral architecture. Methods: Seven species from Geraniaceae and one from Hypseocharitaceae were investigated using scanning electron microscopy and light microscopy. Samples were prepared and processed using standard protocols. Key Results: The development of the nectary glands follows the same trajectory in all species studied. Minor differences occur in the onset of nectarostomata development. The most striking finding is the discovery that a short anthophore develops via intercalary growth at the level of the nectary glands. This anthophore lifts up the entire flower apart from the nectary gland itself and thus plays an important role in floral architecture, especially in the flowers of Pelargonium. Here, the zygomorphic flowers show a particularly extensive receptacular growth, resulting in the formation of a spur-like receptacular cavity ('inner spur'). The nectary gland is hidden at the base of the cavity. Various forms of compartmentalization, culminating in the 'revolver flower' of Geranium maderense, are described. Conclusions: Despite the superficial similarity of the flowers in Geraniaceae and Hypseocharitaceae, there is broad diversity in floral organization and floral architecture. While the receptacular origin of the spur-like cavity in Pelargonium had already been described, anthophore formation via intercalary growth of the receptacle in the other genera had not been previously documented. In the context of the most recent phylogenies of the families, an evolutionary series for the floral architecture is proposed, underscoring the importance of synorganization in these seemingly simple flowers.

Geraniales flowers revisited: evolutionary trends in floral nectaries.

BACKGROUND AND AIMS: The detailed relationships in Geraniales in their current circumscription have only recently been clarified. The disparate floral morphologies and especially the nectaries of the corresponding group have consequently not previously been studied in a phylogenetic context. METHODS: The present study investigates floral and especially nectary morphology and structure for representatives of 12 of the 13 currently accepted genera in the five families of the Geraniales. Flowers were studied using light microscopy and scanning electron microscopy. KEY RESULTS: The data demonstrate the derivation of even the most disparate floral morphologies from a basic pentamerous and pentacyclic organization, with an obdiplostemonous androecium and receptacular nectaries associated with the antesepalous stamens. Divergent morphologies are explained by modifications of merosity (tetramerous flowers), symmetry (several transitions to zygomorphic flowers) and elaboration of the nectaries into variously shaped outgrowths and appendages, especially in Francoaceae. The divergent development of nectar glands ultimately leads to either a reduction in their number (to one in some Geraniaceae and Melianthaceae) or their total loss (some Vivianiaceae). CONCLUSIONS: Floral morphology of the Geraniales shows a high degree of similarity, despite the variation in overall floral appearance and nectary morphology. A hypothesis on the transformation of the nectaries within the Geraniales is presented.

Hygroscopic movements in Geraniaceae: the structural variations that are responsible for coiling or bending.

The family Geraniaceae is characterized by a beak-like fruit, consisting of five seeds appended by a tapering awn. The awns exhibit coiling or bending hygroscopic movement as part of the seed dispersal strategy. Here we explain the variation in the hygroscopic reaction based on structural principles. We examined five representative species from three genera: Erodium, Geranium, and Pelargonium. Using X-ray diffraction, and electron and polarized light microscopy, we measured the cellulose microfibril angles in relation to the cell and cellulose helix axes. The behavior of separated single cells during dehydration was also examined. A bi-layered structure characterizes all the representative genera studied, with a hygroscopically contracting inner layer, and a stiff outer layer. We found that the cellulose arrangement in the inner layer is responsible for the type of awn deformation (coiling or bending). In three of the five awns examined, we identified an additional coiling outer sublayer, which adds coiling deformation to the awn. We divide the movements into three types: bending, coiling, and coiled-bending. All movement types are found in the Geranium genus. These characteristics are of importance for understanding the evolution of seed dispersal mechanisms in the Geraniaceae family.

Tilted cellulose arrangement as a novel mechanism for hygroscopic coiling in the stork's bill awn.

The sessile nature of plants demands the development of seed-dispersal mechanisms to establish new growing loci. Dispersal strategies of many species involve drying of the dispersal unit, which induces directed contraction and movement based on changing environmental humidity. The majority of researched hygroscopic dispersal mechanisms are based on a bilayered structure. Here, we investigate the motility of the stork's bill (Erodium) seeds that relies on the tightening and loosening of a helical awn to propel itself across the surface into a safe germination place. We show that this movement is based on a specialized single layer consisting of a mechanically uniform tissue. A cell wall structure with cellulose microfibrils arranged in an unusually tilted helix causes each cell to spiral. These cells generate a macroscopic coil by spiralling collectively. A simple model made from a thread embedded in an isotropic foam matrix shows that this cellulose arrangement is indeed sufficient to induce the spiralling of the cells.

Synorganisation without organ fusion in the flowers of Geranium robertianum (Geraniaceae) and its not so trivial obdiplostemony.

BACKGROUND AND AIMS: Synorganisation of floral organs, an important means in angiosperm flower evolution, is mostly realized by congenital or post-genital organ fusion. Intimate synorganisation of many floral organs without fusion, as present in Geranium robertianum, is poorly known and needs to be studied. Obdiplostemony, the seemingly reversed position of two stamen whorls, widely distributed in core eudicots, has been the subject of much attention, but there is confusion in the literature. Obdiplostemony occurs in Geranium and whether and how it is involved in this synorganisation is explored here. METHODS: Floral development and architecture were studied with light microscopy based on microtome section series and with scanning electron microscopy. KEY RESULTS: Intimate synorganisation of floral organs is effected by the formation of five separate nectar canals for the proboscis of pollinators. Each nectar canal is formed by six adjacent organs from four organ whorls. In addition, the sepals are hooked together by the formation of longitudinal ribs and grooves, and provide a firm scaffold for the canals. Obdiplostemony provides a guide rail within each canal formed by the flanks of the antepetalous stamen filaments. CONCLUSIONS: Intimate synorganisation in flowers can be realized without any fusion, and obdiplostemony may play a role in this synorganisation.

[Pharmacognostical studies on root of Geranium strictipes].

OBJECTIVE: To establish pharmacognostical methods on Root of Geranium strictipes. METHODS: To study by the original plant identification, character identification. The organizational structure of root and powder features of this drug were observed and compared. TLC of the drug was also undertaken. RESULTS: It showed that Geranium strictipes powder microstructure contained many calcium oxalate cluster crystals and starch grains. TLC had good reappearance. CONCLUSION: This study provides reference information for further development and identification of this crude drug.

Root, stem and leaf anatomy of Geranium palustre Torner Cent. (Geraniaceae).

An anatomical study on the root, stem and leaf of Geranium palustre Torner Cent. has been performed in order to continue our previous researches on this species. Technique of inclusion into paraffin and optical microscope have been used. Root, stem and leaf transverse sections were studied. They contain calcium oxalate crystals as inclusions. The root presents elements of secondary structure (suber, secondary cortex, secondary xylem and phloem). The vascular bundles in the stem can be classified as internal or external and differ in the presence or absence of an own sclerenchyma sheet depending on their age. The vascular bundles of stem are collateral. Leaf structure is bi-facial. Stem and leaf surface have no glandular hairs.

[Pharmcognostial study on the Geranium wilfordii var. glandulosum].

First time has done pharmcognostical research on the Geranium wilfordii Maxim var. glandulosum Z. M. Tan, including microscopic identification, chemical qualitative test and bacteriostatic test.