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Rosemary is an erect, bushy shrub that may reach 2 m in height. Its evergreen leaves are dark green above and white hairy below. The leaves are 2 to 3.5 cm in length and are folded inward along the margins. The violet-blue or whitish flowers are borne in small axillary (i.e., emerging from the angle between the leaf and stem) racemes. The calyx (the collective term for all the sepals of a flower) and corolla (the collective term for all the petals in a flower) are two-lipped, the latter around 1.25 cm in length and enclosing two stamens, the male sex organs in a flower.
(Vaughan and Geissler 1997)
As is the case for mints (family Lamiaceae) in general, Rosemary plants are self-compatible (i.e., they can fertilize themselves), but as is also typical for the family, the anthers (male pollen-producing structures in each flower) are finished producing pollen before the stigmas (female parts) in the same flower mature. Thus, the plants rely on insect pollinators to move their pollen from one flower to another. Often, pollen from one flower is moved to a mature stigma on another flower on the same plant, resulting in self-fertilization. Self-fertilization in Rosemary plants tends to result in fewer and lighter seeds than cross-fertilization (i.e., fertilization of a flower by pollen from a flower on a different individual plant), an example of inbreeding depression. Like many species in the Lamiaceae, Rosemary is gynodioecious, i.e., populations are composed of some plants with hermaphrodite flowers, which are functionally both male and female, and others whose flowers are functionally female, with the male organs reduced and sterile. Hidalgo and Ubera (2001) suggested that gynodioecy in Rosemary effectively increases outcrossing and thereby decreases inbreeding depression.