The plant material (aerial parts) was collected at Corniglia (Liguria, Italy; 44° 07′ N, 09° 43′ E), on calcareous soil at 0-20 m above the sea level during year 1997 at various vegetative periods (May, June, July, September and December). obtaining six samples: (1) stems and leaves (May); (2) stems, leaves and flower buds (June); (3) stems, leaves and flowers (July); (4) stems, leaves, ripe fruits (September); (5) fruits only (September); (6) stems and leaves (December).

The main constituent of the essential oil was always gamma-terpinene (41-68%); sabinene was present in high amount only during fruit ripening (30%), while dillapiole reached its maximum value in December (10%).

The leaves of C. sempervirens were collected in the region of central Dalmatia (Croatia) within 12 months (1999).

The oils produced in the autumn (September and October) were found to contain higher amounts of alpha-pinene (71.0% and 79.2%) than the oils produced from February to May (28.4-32.5%). The smallest amount of alpha-pinene (28.4%) was recorded in February, at the same time as the amount of cedrol, the quantitatively most important oxygenated compound, reached its maximum (12.9%).

The peppermint material was obtained from ten cultivation sites (four growers) around Le Mayetde-Montagne, Allier, France (altitude 400 to 800 m). The individual surface areas ranged from 0.6 to 2.5 ha for an overall surface of 8 to 10 ha. Planting density was 30,000 plants/ha.

A marked inversion of the menthol/menthone ratio was observed according to harvesting time. The late blooming period gave oils rich in menthol. A second harvest gave a high-quality oil and increased overall yield. Pre-drying did not affect the chemical composition of the oil obtained but allowed larger amounts of plant material to be distilled. In particular, Bouverat-Bernier showed an increase in oil yield up to flowering and a fall thereafter and an increase of levels of menthol and menthyl acetate while those of menthone decreased from June to September. For Hungarian peppermint, the levels of menthone were always greater than those of menthol regardless of harvest time.

Plant material: Leaves of M. spicata plants were collected from a wild population of Mt. Pangeon (alt. 600 m, 40° 55′ N/ 24° 12′ E). Collections were conducted every month during the growing period (April to October).

The oil content ranged from 0.1-1.8%, with the maximum values in late summer/early autumn. The essential oil obtained from the leaves was characterized by a very high content in linalool, i.e. 85.0-93.9% of the total oil (highest percentage in mid-autumn). Other oil constituents occurring in much lower amounts were germacrene D (up to 4.2%), beta-caryophyllene (up to 2.6%) and 1,8-cineole (up to 2.1%).

Myrtle (M. communis var. italica) aerial parts were collected monthly during 2006-2007 from Jbal Stara of Haouaria region in North Tunisia, belonging to a subhumid bioclimate.

In conclusion, high fluctuations were observed in the oil yields and composition of different parts of Myrtus communis var. italica during all the collecting periods. They could be explained by genetic and environmental factors. Moreover, significant differences were revealed in the main oil compounds. alpha-Pinene percentages showed the most remarkable changes among the different part oils. So, leaf oils contained more alpha-pinene than those of the fruits and stems during the myrtle vegetative cycle.