Ecophysiological aspects of seed germination were investigated in the widely distributed Mediterranean-endemic, aromatic plants thyme (Coridothymus capitatus), savory (Satureja thymbra) and oregano (Origanum vulgaresubsp.hirtum). Thyme seed germination is light indifferent, whereas oregano seeds have an absolute light requirement; their germination can be promoted even by green safelight or far-red light. In savory, a portion of the seeds germinates in the dark and germination can be either increased or decreased by the appropriate illumination. All three species show more germination at a relatively low temperature range, a Mediterranean characteristic, with an optimum around 15–20°C. The rate of germination is considerably higher in the tiny seeds of thyme and oregano than in the larger seeds of savory. In the latter species, germination is also dependent upon the age of the seeds; old seeds germinate to a higher percentage than fresh ones, as already observed by Theophrastus, possibly as a result of the volatilization of the essential oils present on the nutlet coat. Seeds of thyme, savory and oregano are dispersed within the persistent fruiting calyces and the seeds eventually germinate within it. Essential oils in the calyx strongly inhibit germination of the enclosed seeds; germination is much suppressed in thyme and to a lesser extent in savory and oregano. This diaspore dormancy caused by essential oils apparently is overcome under natural conditions by leaching of the inhibitors with rainwater. It is suggested that this dormancy operates as an adaptation strategy that delays germination by acting as a rain gauge. In this way, seed germination and subsequent seedling establishment are prevented during the early phase of the rainy period, which is usually interrupted by drought spells in the Mediterranean climate.

International audienc

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The present study examined seed dispersal and germination in three of the most threatened endemic labiates of Cyprus: Origanum cordifolium, Phlomis brevibracteata and Phlomis cypria ssp. occidentalis. Some common traits in these taxa can be correlated with their overall survival strategy. Seeds mature in mid to late summer, but most seeds remain on the mother plants until the beginning of the rainy season. The opening of the calyces containing the seeds seems to be caused by absorption of moisture. Water is also the most important dispersal factor because the seeds are dispersed by rain. Seed germination occurs at relatively low temperatures that prevail in the field at the beginning of the rainy season. This behavior provides the plants with ecological advantages because their seeds are exposed on the soil at the most appropriate period (mid to late autumn) for germination and seedling survival. The present study contributes substantially to in situ and ex situ conservation of these threatened plants.

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