## 3 Functions of \(\beta\)-Ocimene in Flowers  
Ocimene is likely to play major ecological roles in flowers due to its commonness and abundance in floral scents. _Trans_-\(\beta\)-ocimene occurs in the floral scents of 71% of the 90 plant families in the list of identified floral-scent compounds compiled by [PERSON] et al. [1]. In our recent metaanalysis of floral scents [9], _trans_-\(\beta\)-ocimene occurred in the floral scents of 47.5% of the 291 plant species  
Figure 1: Chemical structure of the two \(\beta\)-ocimene stereoisomers, _cis_- and _trans_-\(\beta\)-ocimene (also referred to as (\(Z\))- and (\(E\))-\(\beta\)-ocimene, respectively). (Figure 2) and in 75% of the 63 plant families represented. The presence of this compound in nearly a half of the species that were considered in our study may seem not too much at first glance, but when we look at the other compounds we may see that few compounds present similar levels of occurrence and predominance in floral scents (Figure 2). The ability to emit \(\beta\)-ocimene from flowers is widely distributed and has appeared and disappeared several times across the phylogeny of flowering plants (Figure 3). It is abundantly emitted by a wide range of plants that are pollinated by various groups of pollinators, including bees [20; 21], beetles [22; 23], butterflies and moths [22; 24; 25]. [PERSON] et al. [26] proposed that \(\beta\)-ocimene was a generalist pollinator attractant, arguing that \(\beta\)-ocimene was emitted in high proportions by the generalist species _Muscari neglectum_, _Ranunculus gramineus_, _Euphoria flavicoma_ and _Iris lutscens_. These four species were rare at the study site in a Mediterranean shrubland community and were submitted to strong competition for pollinator visitation by the dominant plant species _Rosmarinus officinalis_ and _Thynus vulgaris_. The authors also argued that all rare species that co-flowered and had to compete with _R. officinalis_ and _T. vulgaris_ emitted floral scents dominated by \(\beta\)-ocimene, because this volatile compound may help them to effectively attract a wide array of pollinators and thus to compensate for the plants' low abundance. Alternatively, the dominant species, _R. officinalis_ and _T. vulgaris_, may emit more complex floral scents, which are very rich in other terpene compounds [26]. Attracting specialized pollinators that transfer pollen only from the same plant species provides several advantages for plants, compared to relying on a generalized pollination [27]. We could thus hypothesize that several plant species growing as a community reassemble a large community of pollinators by producing a global flower signal, while minor VOCs or other traits could then insure specificity in the flowers visited by pollinators. Figure 2: Occurrence and abundance of \(\beta\)-ocimene in floral scents. Bar charts showing (**a**) the percentage of plant species with the most common floral volatiles; (**b**) the percentage of plant species where the most abundant floral volatiles represent more than 25% of the total floral scent; and (**c**) the percentage of plant species where the most abundant floral volatiles represent more than 50% of the total floral scent. Multiple evidence supports the role of \(\beta\)-ocimene in pollinator attraction in addition to its high occurrence in floral scents. \(\beta\)-Ocimene can effectively attract honeybees and bumblebees [28; 29]. Animal-pollinated flowers have evolved mechanisms to regulate VOC emissions and make them follow particular spatial and temporal patterns of emission in order to maximize pollinator attraction and pollination success [14; 30]. Spatial patterns of emission along petals or in particular organs of the flower can resemble visual nectar guides and constitute reliable guides for pollinators to find and reach the nectaries, while normally ensuring pollinator contact with the pollen and the stigmas [31].