Pollinator adaptation to oil-secreting flowers-rediviva and diascia.

We used the Mixta+ and mixta- lines of Antirrhinum majus as a model system to investigate the effects of epidermal cell shape and pigmentation on tissue optical properties in the visible and ultraviolet (UV) spectral regions. Adaxial epidermal cells of Mixta+ flowers have a conical-papillate shape; in the mixta- line the cells are slightly domed. Mixta+ cells contained significantly more anthocyanin and other flavonoids than mixta- cells when plants were grown under either high- or low-UV conditions. Mixta+ cells focused light (3.5-4.7 times incident) within their pigmented interiors, whereas mixta- cells focused light (2.1-2.7 times incident) in the unpigmented mesophyll. UV light penetrated the epidermis (commonly 20-50% transmittance at 312 nm) mainly through the unpigmented peripheral regions of the cells that were similar for the two lines, so that overall penetration through Mixta+ and mixta- epidermises was equal. However, maximum UV absorption in the central region of epidermal cells was slightly greater in Mixta+ than mixta-, and intact Mixta+ flowers reflected less light in the spectral regions with intermediate flavonoid absorbance. In both cases, about 50 to 75% of the difference could be attributed to cell shape and resulting changes in the optical pathlength or focusing.

Effects of Epidermal Cell Shape and Pigmentation on Optical Properties of Antirrhinum Petals at Visible and Ultraviolet Wavelengths.

The flowers of the Scrophulariaceae show a great diversity in form, especially of the corolla. The most common pollinators are bees collecting nectar, pollen, or oil; other pollinators are moths and butterflies, hummingbirds, syrphid flies, and (in one case) ants. The occurrence of bell-shaped corollas in most tribes of the Scrophulariaceae and in related families indicates that this is the basic (ancestral) flower form. Derived from it are narrow tubular corollas, wide flaring ones, corollas closed to unsuitable visitors by a palate (an upcurving of the tube), corollas forming a keel around the style and anthers either on the upper or lower side of the flower, corollas inflated to form a balloon, and corollas with one or two spurs. Convergences due to selection by the same or similar pollinators limit the usefulness of most of these floral features in analyzing the systematic relationships of the tribes of the Scrophulariaceae. Nevertheless, their diversity of forms exemplifies the evolutionary potential of fused perianth parts.

Pollination and flower diversity in scrophulariaceae

The literature on African pollination biology is reviewed. It is found that relatively little work has been done on pollination biology in Africa, and a very small proportion of pollination relationships has so far been studied. Much of the research which has been done is of an evolutionary nature. Very little work has been conducted at the community level and comparatively little applied work, either to agriculture or conservation, was encountered. Most research has been conducted in South Africa, in particular, from the Cape region, which is the only part of Africa for which a reasonably comprehensive body of work on pollination biology exists. In a number of instances results of African studies challenge conventional understanding of pollination biology. It is argued that as more work on pollination is done in Africa, more differences between African systems and the rest of the world, particularly the North temperate regions will be found and changes to the overall conceptualization of pollination systems in different ecosystems are likely to ensue. A more thorough understanding of pollination biology would also make an important contribution to food security and conservation of biodiversity on the continent. Scientists working in fields other than pollination biology, and amateurs, should be encouraged to contribute to the groundwork of African pollination biology by the documentation of pollination relationships.

African pollination studies: where are the gaps?

Lunau, K.: Stamens and mimic stamens as components of floral colour patterns. — Bot. Jahrb. Syst. 127: 13–41. 2007. — ISSN 0006-8152. Dedicated to Professor Dr. Gunther Osche, Freiburg im Breisgau (Germany), on the occasion of his 80th birthday; he discovered the phenomenon of mimic stamens when re-assessing floral colour pattern with his eyes newly tuned by Wicklerian thoughts about automimicry. Stamens of zoophilous plants are multifunctional floral organs which protect pollen against environmental stress, attract potential pollinators, attach pollen to the sites of secondary pollen presentation, or to the pollinator’s body surface, and provide pollen as a reward for flower-visitors. Pollen-eating flower-visitors such as syrphid flies and pollencollecting flower-visitors such as bees innately respond to visual and chemical cues of stamens and pollen prior to individual experience. Flowering plants presenting conspicuous stamens and pollen to attract pollinators incur numerous costs associated with visual exposure of pollen including investments for protection against solar radiation, pollen losses caused by wind, rain, and illegitimate flower-visitation, and pollen losses due to consumption of pollen by flower-visitors or pollinators. Many flowers use mimic stamens (e.g. staminodes, false stamens, yellow floral guides in the size and shape of anthers) and thus overcome these disadvantages. Several study cases focus on the benefits of signaling with mimic stamens in flowering plants having polymorphic flowers, distinct flowering phases, and hidden real pollen. The aim of this review is to illustrate the various cases in which flowering plants may benefit from attracting flower-visitors by means of mimic stamens.

Kim E. Steiner

Papers

The Diascia (Scrophulariaceae) window: an orientation cue for oil-collecting bees.