Towards an integrative understanding of stamen–corolla tube modifications and floral architecture in Boraginaceae s.s. (Boraginales)

Morphological studies rarely address floral organ modifications or their integration into floral architecture and floral function. Boraginaceae show two prominent types of stamen–corolla tube modifications: faucal and basal scales. Both types, especially faucal scales, are widely used in classification. Here, the ontogeny and morphology of faucal and basal scales are studied in 29 species from eight tribes and all three subfamilies of Boraginaceae s.s. (=Boraginoideae sensu APG IV) using scanning electron microscopy. Integration into floral architecture is visualized with micro-computed tomography (µCT). Faucal and basal scales are present in 18 and 27 species, respectively. Both types of scales develop late in flower ontogeny, but with variable timing. Faucal scales are morphologically far more variable than basal scales. Faucal scales are located close to the anthers and sometimes are involved in anther cone formation. Basal scales cover either the gynoecial disc nectary or the entire ovary. The different scale morphologies identified here enclose complex internal spaces, but they show no obvious phylogenetic patterns. This probably indicates strong functional constraints and adaptive pressures. This is a first in-depth study of the morphology and development of stamen–corolla tube modifications in Boraginaceae s.s., demonstrating that in situ three-dimensional visualization of floral architecture with µCT provides unprecedented insights into the evolution and functional integration of stamen–corolla tube modifications in Boraginales.

Floral organogenesis in Dysosma versipellis (Berberidaceae) and its systematic implications

The Berberidaceae and the six other families of Ranunculales form a sister clade to all other eudicots, and are crucial to reconstructing the common ancestor of flowering plants. Previous studies have suggested that the petals of most Berberidaceae are derived from stamens, and some are thought to develop petals from common petal/stamen primordia. However, the flower ontogeny is still poorly known in the family and the presence of common primordia needs to be re-evaluated from a comparative developmental perspective. Here, we used scanning electron microscopy to study the floral development of the endemic Chinese species Dysosma versipellis (Hance) M. Cheng ex Ying, which was originally placed in Podophyllum. Our results show that the floral organs are all free and the sepals, petals, and stamens are initiated centripetally in successive and alternate trimerous pairs of whorls around a single carpel. The nectarless petals are initiated separately and do not develop from common primordia with the stamens. Floral and developmental features of D. versipellis are similar to those of most members of Berberidaceae. The regular development of multiple flowers and absence of a secondary increase in the number of stamens in Dysosma support its exclusion from Podophyllum, and this is also inferred by the DNA sequence data.

Nectar production in species of the Genus galanthus L. (Amaryllidaceae) from Serbia

As a contribution to the study of the melliferous flora of Serbia, nectar production in two species of the genus Galanthus L. (G. nivalis L., and G. elwesii Hook.) was investigated. The intensity of nectar secretion was determined directly, using the microcapillary method. The study included determination of the total daily nectar amount per flower, and an analysis of nectar secretion dynamics during the day and during the flower ontogeny. The results show that the total daily amount of nectar per flower is low, and flowers of both species exude nectar only once during the day and during the flower ontogeny. However, despite the low nectar production, Galanthus species represent a first valuable source of nectar and pollen to pollinators in the early spring period, when only a small number of species are in the flowering phenophase.

Flower and Pod Abscission Due to Heat Stress in Beans

The effect of high temperature on abscission of bean (Phaseolus vulgaris L.) flowers and pods was studied under growth chamber and greenhouse conditions. Experiments investigated stages at which flowers are sensitive to heat stress, the period when reproductive structures abscise, and sensitivity of male and female flower parts to heat stress. Heat treatments (2 days at 35C, 10 hours per day) were applied through flower ontogeny, from 8 days before anthesis until anthesis. The flower bud stages were defined by correlating the pedicel length with days to reach anthesis. The prefertilization period showing highest sensitivity to heat stress extended from ≈ 6 days before anthesis to anthesis. We found that 82% of heat-stressed structures abscised as small pods (< 2 cm in length), even when the stress was applied at various flower bud stages. Reciprocal crosses made with pollen from heated plants or on heat-treated flowers indicated that pollen was more affected by heat stress than by female structures.