## 3 Discussion  
A HS-SPME/GC-MS technique was used to identify the volatile compounds of 14 unscented or faint-scented flowers of species and hybrids of the _Tillandsia_ genus. For the extraction using the HS-SPME technique, a CAR/PDMS fiber was chosen and performed with two different extraction methods differenced by time and temperature values, which allowed an efficient extraction of the aromatic components. Indeed, two other fibers were tested--PDMS and CAR/PDMS/DVB. The CAR/PDMS fiber proved to be more efficient by extracting the maximum of compounds in _T. bergeri_ flowers. Considering the volatility of analytes affecting the optimal conditions of temperature and extraction time, two extraction methods were necessary to extract the majority of volatiles emitted by _Tillandsia_ flowers [26]. The aromatic profiles of the 14 species were obtained by GC-MS analysis. First, the results showed that the number of volatile compounds present in each profile is quite low. Between 6 and 25 compounds per analyzed species were identified in the 14 profiles. In the precedent study of our laboratory, using the same extraction conditions, 30 compounds were identified in the fragrant flowers of _T. xiplioides_[26], 47 compounds in _T. croata_, and 43 compounds in _T. caliginosa_[27]. These results now reported showed some differences between the profiles of the unscented or faint-scented species studied here. Indeed, _T. paleacea_ and _T. bandensis_ are two species that are very different from the others. Their aromatic profiles have higher intensities in monoterepenes compared to the other flowers' species. This can be explained as these two flowers are considered more odorant compared to the 12 other species that are scentless for humans [31; 32]. This is confirmed by the interpretation of the heatmap (Figure 1), where it is possible to see the specific compounds identified in both T. _paleacea_ and T. _bandensis_. Although these two species are both faint-scented to humans, they present a different aromatic profile between each other. In _T. paleacea_, as the other species, the eight volatile compounds, benzaldehyde (22), benzacetaldehyde (24), hexanol (40), hexanal (43), heptanal (44), octanal (47), nonanal (49), and furan-2-pentyl (59) were identified whereas only benzaldehyde (22) and nonanal (49) where identified in _T. bandensis_. Moreover, 10 compounds were identified only in _T. bandensis_, methyl-eugenol (37), eugenol (30), tetradecanal (54), hexadecanal (55), hexadecanol (42), methyl ortho-anisate (35), methyl-nicothinate (61), terpinolene (11), \(\gamma\)-terpinene (10), and isomyocorene (7). On the contrary, _T. didisticha_'s aromatic profile is very poor. With the two methods, only six compounds were extracted and identified in this species. By regarding the first PCA (Figure 2), _T. aeranthos_, _T. bergeri_ and hybrids _T. aeranthos x T. bergeri_ can be well separated, which means their aromatic profile is distinctly different between each other's. Indeed, sesquiterpenoids are specific to _T. aeranthos_ while phenylpropionoids/benzenoids are specific to _T. bergeri_. Concerning the second PCA (Figure 3) in which _T. paleacea_, _T. bandensis_, _T. didisticha_, _T. recurrata_, _T. albertiana_, and _T. xixoides_ were excluded, the separation of the eight remaining species is more difficult than previously thought. The aromatic profiles of these eight _Tillandsia_ species and hybrids share more similarities to each other. This could be explained by the fact that five of them belong to the same subgenus group: _Anoplpython_ (_T. aeranthos_, _T. bergeri_, _T. aeranthos x T. bergeri_, _T. aeranthos 'uruguay'_, and _T. tenuifolia_). The olfactory sensitivity and system are not the same between humans and pollinators. Moreover, between humans, the detection level of odors can vary. The combination of VOCs emitted by a plant allows the pollinators to extract information about the plant species, the nectar available, and its quality [33].