While the various bromeliad registries contain a lot of useful information on bromeliads, they have limited information on tillandsia species whose flowers are fragrant.
Barry Stevenson and Sharon Lee recently compiled a list of these species—see https://www.facebook.com/notes/tillandsia-addicts-australia-buy-swap-sell-share/perfumed-tillandsia-species/1020508584752961/
Their list, along with some additions from other sources, is: arequitae, arhiza, aurea, bandensis, brealitoensis, cacticola, caerulea, caliginosa, cotagoitensis, crocata, diaguitensis, disticha, duratii, funebris, graomogolensis, humilis, ixoides, jucunda, kuehasii, kurt-horstii (now graomogolensis), linearis, mallemontii, mereliana, myosura, nuptialis, paleacea, pieranoi, prolata, purpurea, reichenbachii, remota, straminea, streptocarpa, streptophylla, tafiensis, tenebra, umbellata, usneoides, xiphioides, and yuncharaensis.
While many of these species are readily available, some are rare.
Some fragrant species which you may see (and smell!) that have been reclassified away from the Tillandsia genus are:
Lemeltonia acosta-solisii, cornuta, dodsonii, triglochnioides, monadelpha, narthecioides, scaligera, triglochinoides,
Racinaea dyeriana, hamaleana, venusta,
Wallisia pretiosa, lindeniana.
The type of fragrance emitted by each of the fragrant tillandsias is very much in “the eye (or nose!) of the beholder”. So, I will not attempt to describe them in this article.
The strength (or concentration) of a fragrance will be greater when:
• You have a group of plants from a species growing together, rather than having them spaced out. (A bromeliad pioneer, Grace Goode, had a “wall” of Tillandsia mallemontii, whose fragrance could be detected 15 metres’ away. She created the wall by tying individual plants to chicken wire mesh. As they developed into clumps, the amount/strength of fragrance at flowering time became very pronounced);
• Fragrance strength will often be more pronounced in the early morning or in the evening, reflecting the frequent lack of wind at these times;
• If the flowering plants are growing in a confined space i.e. where there is relatively little air movement to dilute the fragrance, then the fragrance strength can be quite pronounced;
• The plant produces large numbers of flowers e.g. T. duratii;
• The fragrance strength of individual flowers will usually be most pronounced when they are receptive to fertilisation, as the fragrance acts as an attractant for pollinators; and • Some clones of a particular species may produce more fragrance than others.
Small fragrant tillandsias which are reasonably common include: bandensis, caliginosa, caerulea, crocata, mallemontii, myosura, triglochnioides and usneoides (Spanish Moss).
Medium size ones include: cacticola, humilis, ixoides, jucunda, linearis, mereliana, streptocarpa, and xiphioides.
Larger ones include: disticha, duratii, paleacea (some forms), purpurea, straminea (some forms), and streptophylla.
A hybrid of any two of fragrant species is highly likely to produce offspring with fragrant flowers.
Some species (for example: crocata, duratii, mallemontii and usneoides) often produce some fragrant flowering offspring, when crossed with a non-fragrant species.
So, if you are interested in growing tillandsia hybrids, you may wish to add fragrance to your list of desirable attributes.
I would like to thank the members of the Tillnuts’ discussion group for their comments on a draft of this article.
But what is it that our senses are reacting to?
As with all plants, alluring Tillandsia fragrances are actually a mixture of volatile organic compounds (VOCs) and low-molecular-weight lipophilic (oil- and fat-soluble) liquids. VOCs include alcohols, aldehydes, ketones, esters, and other miscellaneous hydrocarbons. Across 90 different plant families, more than 1,700 VOCs have been identified.
A fragrance can comprise of a mixture of over 100 different compounds, many at concentrations as low as 1 part per 30 billion, and it is it is the unique combinations of VOCs specific to each plant species — especially those that are prevalent — that give rise to the distinctive fragrances we associate with each bloom. Our facility to sense Tillandsia fragrances relies on our unique chemoreception sensors in our nose. The internal cells of the nose contain olfactory receptors which can bind to the odorant molecules entering the nose changing the overall shape of the molecule. This triggers a series of reactions that informs our brain the nature of the fragrance. Over 390 olfactory receptors have been identified, which can detect thousands of different odorant chemicals. Different receptors may be specific or generic to odorant binding. The unique set of receptors a person has is determined genetically, making sensing a smell personally exclusive. Based simply on which active receptors you have; a fragrance may seem strong while someone else may not detect any aroma at all.
Colour can be defined as primaries; red, blue, yellow with secondary components; orange, violet, green, but describing a smell is much more elusive. By comparison, this makes communicating a fragrance or “smell” difficult. Like the taste of wine, defining a fragrance can be elusive and highly subjective.
The range of fragrances across Tillandsia species and hybrids is wide and descriptions range from:
• delicately sweet
• with a lightly sweetly fragrant
• highly fragrant with a cinnamon scent
• amazingly strong fragrance
• a delicate perfume like a Cattleya orchid
• gardenia-like scent
• citrus- carnation scented
• mildly fragrant
• soft sweet fragrance
When we also consider that fragrances are associated with feelings, emotions, and memories descriptions become even more complex.
However, we can draw analogies with a piece of music. Consider a fragrance that can have a combination of top, middle, and base notes. The top notes are the most volatile compounds, while the base notes are the least volatile. Volatility plays a role in how long a scent lingers, which can be anywhere from minutes to hours. Volatility can also impact how molecules bind to each other or chemicals in the environment.
In most cases, Tillandsias are emitting alluring fragrances as part of the pollination process. They do this to communicate with each other plants or as a means to attract pollinators such as insects, bats, or birds. In some species the fragrance is very delicate, while in others it is very strong. Like any plant, a Tillandsia’s production of VOCs is an energy-intensive process, and to balance the use of resources, specific species only produce scent chemicals during specific times. In some species the fragrance is strongest at mid-day when there is bright sunlight, while others only reveal their secret sent during the darkness. For others temperature plays a role.
There may be many more Tillandsias that produce a subtle scent which is within the range of pollinators like birds, insects and bats but the perfume is beyond human perception.
Fragrances are complex and as mentioned can be a mixture of over 100 VOCs. The plant may produce specific VOCs in varying amounts at different times of a 24 hour cycle. Fluctuations in temperature, humidity or even atmospheric pressure may alter the combination. It may also be that when different populations of a species grown from seed mature that produce variable combinations of VOCs, which might explain why some sources quote T. cacticola and T. palaeacea as fragrant while other sources dispute this.
Some of them, like arequitae, cacticola, ixioides, nuptialis and streptophylla, I’ve not noticed were fragrant though, nor dyeriana, jucunda and paleacea.
(Note that Walter Till also told me that W. umbellata stays as a separate taxon, separate from Lindeniana, after some discussion a few years ago.)