Photoinhibition of seed germination was shown for Allium staticiforme, Brassica tournefortii, Cakile maritima and Otanthus maritimus, all plant species inhabiting sandy coasts of the Mediterranean Sea. Germination of A. staticiforme was found to be typically Mediterranean in regard to its temperature range (>0–20 °C), while B. tournefortii germinated optimally at intermediate temperatures (15–25 °C). Light sensitivity was more pronounced in the latter species and 50 % inhibition of seed germination was obtained with photon flux densities of approximately 0.1 and 0.015 mol m⁻² d⁻¹ in A. staticiforme and B. tournefortii, respectively. However, the slopes of the regression lines of germination plotted against the logarithm of white light flux density are similar in both species. From monthly experiments performed under fluctuating conditions of temperature and light, simulating the elimate of Athens throughout the year, optimal germination response peaked in ‘winter’ conditions for A. staticiforme, while a bimodal pattern was observed for B. tournefortii (maxima at the warm ends of the rainy season). In contrast to the other plants, a fifth species tested, Crithmum maritimum, showed an absolute light requirement, probably related to the rocky habitats of the species; the optimum germination period coincided with the rainy season. Pot experiments with seeds of the five species buried at various depths confirmed that maximum emergence is favoured by shallow depths (0.5–1 cm). It is concluded that seed germination in maritime plants of the Mediterranean rim is mediated by a photoinhibition mechanism which can be considered an adaptation strategy against surface seedling establishment at the harsh, sandy or shingle, sea coast habitats.

We examined the relationship between plant species richness and biogeographical variables (island area, island maximum elevation, distance from nearest inhabited island, distance from nearest mainland) using a data set comprising 201 islands of the Aegean archipelago. We found that endemic species richness was strongly correlated to total species richness. Single-island endemic species richness was most strongly correlated to island maximum elevation, and then to island area, with an apparent small island effect for islands smaller than 47 km². Total species richness was most strongly correlated to island area (with no apparent small island effect), and less strongly correlated to island maximum elevation. Distance from the mainland or other inhabited islands displayed limited predictive value in our data set. The slope of the relationship between species richness and geographical factors (island area, elevation, distance from island/mainland) was steeper for endemic species richness than for total richness. Finally, the different scales of endemicity (single-island endemics, island group endemics and Aegean regional endemics) displayed similar qualitative trends and only differed quantitatively. Thus, we conclude that different biogeographical factors act as drivers for total species richness than for endemic species richness.

The yellow horned-poppy Glaucium flavum Crantz shows a final dark germination which is of characteristically ‘mediterranean’ type (maximal response at the temperature range 5–15 °C), though a considerable broadening is brought about, both by a red light pulse and a stratification treatment. Seeds imbibed in darkness at 25 °C for even a few hours are induced to develop a secondary dormancy (thermodormancy) which can be released by light and stratification. The well known time dependence of light sensitivity and the gradually imposed induction of light indifference at supraoptimal temperatures have also been shown. Seeds imbibed under regimes simulating those met naturally in Greece during November or April, do not germinate when illuminated with white light (ζ = 1·26). Full manifestation of germination occurs either in complete darkness or under various, red-enriched light conditions (ζ higher than 2·07). A partial promotion is observed with very low fluence rates of white light (in the order 10⁻²−10⁻⁴ of daylight). The existence of a surface-avoiding seedling emergence mechanism based on light-inhibited seed germination was verified in a pot experiment under natural conditions, with seeds buried to various depths. Only those seeds buried at 0·5 cm germinate optimally and readily after the onset of the rainy season (November-December) although those at 1 and 2 cm also germinate to a considerable extent