Gynodioecy, as defined by Darwin in 1877, is the occurrence of two kinds of individuals in natural populations: bisexual or hermaphrodite plants, which here will be called male-fertiles or (Mf), and females, here described as male-steriles or (mS). Many plant species are gynodioecious, but male sterility often occurs only atvery lowfrequencies. Precise counts of mS in natural populations are rare or isolated, however. Only a few species have been extensively sampled. When the frequency of mS reaches a sufficiently high level for the situation to be qualified as a polymorphism, gynodioecy sets an interesting problem related to the breeding system [1]. The processing industry needs high quality, homogenous and standardised raw material. Thus it is important for thyme producers to have high quality cultivars with a good level of homogeneity. Rey et al. (2004) showed that crossing male sterile (MS) with male fertile (MF) plants to breed hybrids is an adequate approach to improve homogeneity of thyme cultivars. The purpose of this study is to determine of percentage of gynodioecious in four population Iranian thyme T. daenensis, T. migricus, T. transcaspicus and T. pubescens collected from Semnan, West Azerbaijan, Khorasan and East Azerbaijan respectively, in Mashhad environmental conditions.This experiment was performed at the Research Station of the Faculty of Agriculture, Ferdowsi university of Mashhad. Highest percentage of gynodioecious observed in T. migricus species with 75 present. The percentage of gynodioecious in T.daenensis, T. transcaspicus and T. pubescens were 58.33, 8 and 9.1 % respectively. Naturalpopulations show very high variation in female frequency, from 5% to 95% depending on the population, with a meanvalue slightly above 60% in southern France. In Thymus vulgaris L. the percentage of mS plants varies greatly, from 5 to 95%. This is a particularly wide variation for a gynodioecious species. In short, female plants carry a CMS gene blocking the development of functionalanthers, while hermaphrodites either do not have such aCMS gene or carry at least one nuclear restorer allele thatrestores male function [2]. Overall, females compared to hermaphrodites produced more but smaller flowers, had higher fruit set, higher total seed production, and produced heavier seeds that germinated better [3].

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