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Ecophysiology of germination in the aromatic plants thyme, savory and oregano (Labiatae)

Published online by Cambridge University Press:  19 September 2008

Costas A. Thanos ,
Costas C. Kadis  and
Flora Skarou
Costas A. Thanos*
Affiliation:
Department of Botany, University of Athens, Athens 15784, Greece
Costas C. Kadis
Affiliation:
Department of Botany, University of Athens, Athens 15784, Greece
Flora Skarou
Affiliation:
Department of Botany, University of Athens, Athens 15784, Greece
*
*Correspondence
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Abstract

Ecophysiological aspects of seed germination were investigated in the widely distributed Mediterranean-endemic, aromatic plants thyme (Coridothymus capitatus), savory (Satureja thymbra) and oregano (Origanum vulgare subsp. 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.

Keywords

Coridothymus capitatusSatureja thymbraOriganum vulgareseed germinationessential oilspersistent calyxphytochrome
Type
Ecology
Information
Seed Science Research , Volume 5 , Issue 3 , September 1995 , pp. 161 - 170
Copyright
Copyright © Cambridge University Press 1995

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