Sweet peas, Wisteria, and Mimosa are well known in the cosmetic and gardening world: striking and lovely. All of these are very different in their habit, region of origin, as well as their floral structure. When there is so much dissimilarity, how do we connect them?
All of the plants listed belong to the Legume family, Fabaceae, and can be traced back to a most recent common ancestor, placing them in a clade. The Fabaceae share common physical traits, such as their floral structure which is composed of a banner, keel, and two wing petals. While the growth pattern of Fabaceae varies from herb, trees, shrubs, or lianas, most of them have alternate leaves, divided compound pinnate leaflets, and similar floral and fruit structures. The fruit of Fabaceae is a legume - a pod that is generally dry and dehiscent (opening) when ripe, originating from one carpel (the structure that develops the plants' ovule in this case). Although this generally means it is a "bean," some species have adaptations and modifications that make the legume look quite different. Identifying the key components of Fabaceae ties all of these species together, but it is the floral scent adaptations that make some species stand out among the others.
Figure 1 Fabaceae general morphology labeled. Very simplified, but you get the point! Created by Dasha Horton 2023 Galaxy Note 10 PENUP.
Scent adaptations in plants are spread across angiosperms (flowering plants) and are not limited to any one family or clade. Flowering plants sometimes have volatiles or oils that are strongly scented to ward off pests, while others attract pollinators (with the assumption of natural selection). Either way, adaptations of scents are not aimed specifically at humans, but we benefit from the sweet aromas and pungent queues that plants give off.
Lathyrus species such as Lathyrus odoratus are commonly known as the “sweet pea”. The flower's first references were from Sicily, Southern Italy, and the Aegean Islands. This is a climbing vine legume with varying flower colors and has been grown for florists, in ornamental gardens, and in a wide range of other industries utilizing its characteristic blooms- especially its olfactory impact. Sweet pea is described by perfume makers as a cross between orange blossom and hyacinth with some rose accents and is found in many leading perfume brands. The strong floral scent has been used in perfumery since the 17th century. However, modernly the scent is a synthetic replica. The smells originate from the chemicals: ( E) and (Z )- ocimene, linalool, nerol, geraniol, and phenylacetaldehyde. These are solely emitted from the banner and keel of the flowers. Ocimene is also in other plants such as hops, kumquats, basil, bergamot, lavender, and orchids. Generally, this chemical is used as the floral and sweet scent in the perfume industry and as an attractant for pollinators such as moths and bees. Another interesting volatile is geraniol which is also synthesized for food and cosmetics as a "rose" scent. It's quite fascinating to note that geraniol is not just a chemical compound found in various plants, but it is also secreted by the scent glands of honeybees. These bees leave behind the scent on flowers as a marker for other bees to easily locate the nectar-rich flora. This natural process is a remarkable example of how honeybees use chemical signals to communicate and work together as a community in search of food.
Figure 2 Lathyrus flower by Dasha Horton 2023
Lupinus, lupine (US), or lupin (UK and Australia), is another legume that has a striking scent and is similar to candy. The flowers are packed in a showy raceme on erect and sturdy stems and the leaves are alternate compound, palmate leaves varying by species. Lupine are insect-pollinated, although nectar is not produced, the vexillum secretes a fragrant liquid. Generally, lupines are avoided by deer, but some species are predated to endangerment by them affecting other fauna. L. perennis is crucial to butterfly larvae, like Karner blue (Plebejus samuelis) which is a specialist. As deer over-graze on the wild lupine, the Karner blue also loses plants to lay eggs on and feed the larvae. Some species with very notable scents are L. arboreus (tree lupine), L. excubitus (grape soda lupine). The latter is said to have a grape soda scent as the common name implies. L. excubitus is a shrub that can grow to 7 ft tall and is a great moth and butterfly attractor. This plant is most known to grow along the western coast of America. Although it smells nice, it is toxic and should not be injested raw. The primary toxic elements are alkaloids like lupenine and sparteine, which are removed through processing.
Figure 3 Lupinus excubitus flowers. Walter Siegmund, CC BY-SA 4.0 <https://creativecommons.org/licenses/by-sa/4.0>, via Wikimedia Commons
Dipteryx odorata, Tonka bean or coumarou is a flowering tree plant native to Northern South America and Central America. The common name coumarou is from the Galibi language spoken in native French Guiana. The previous name, the basonym, was Coumarouna odorata. They produce strongly scented beans that are dark in color and reside in fleshy fruit rather than the standard long pods on other Fabaceae plants. The seeds have high levels of coumarin, which gives them the distinct sweet and woody scent prized by fragrance makers. Coumarin is a chemical compound that is known to be toxic and can cause serious harm to the heart and liver if consumed in large quantities. However, it is important to note that coumarin is still used in some cuisines around the world, albeit in limited amounts. This is because the amount of coumarin required to cause damage to the body is quite high, and most recipes use only a small quantity of this compound. Despite its potential risks, coumarin is valued by many chefs for its unique flavor profile, and it continues to be used in certain dishes and desserts as a natural flavoring agent.
Figure 4 Dipteryx odorata. Tatters 2020 Flickr https://www.flickr.com/photos/tgerus/49829685507/
Wisteria is a stunning ornamental with fragrant flowers and vining habit. It’s often used in landscaping. There are several species in the Wisteria genus including American Wisteria: W. frutescens, Chinese Wisteria: W. sinensis, Japanese Wisteria: W. floribunda, Silky Wisteria from Japan: W. brachybotrys, and Kentucky Wisteria: W. macrostachya. Wisteria has hanging formations of dozens of flowers described as ebracteate inflorescence in pink, purple, white, and even blue coloring. The scent is described as varying from musky to floral sweet. Some people even describe certain varieties as having a “cat pee” scent rather than a floral one. The scent is produced from volatiles and phytochemicals most present when the flowers are in bloom. There are dozens of compounds responsible for the smells, and they are concentrated in the petals, although some notable quantity was emitted from the sepals, pedicels, stamen, and pistils. The links between the floral scent and the less favorable scent of Wisteria have further research needed.
Wisteria floribunda Tanaka Juuyoh 2010 Flickr https://www.flickr.com/photos/tanaka_juuyoh/4616630179
Albizia julibrissin, Mimosa tree or “Persian Silk Tree” is a tree with flowers that appear like bright pink soft feathers dispersed among small compound leaves. This tree is Native to China, Japan, Korea, and parts of the Middle East such as Iran. although it is also an ornamental landscaping tree in other regions. A. julibrissin is named after the Persian (Farsi) word pronounced “gul-I brisham” which also means “silk flower”. This plant is stunning and whimsical to look at and has a delicate floral fragrance used in perfumery. The Mimosa Tree is not the same as Mimosa Plants which are in the Mimosa genus and are characterized by similar compound leaves and much smaller flowers. Additionally, species of the genus Acacia are called Mimosa, these too are closely related but have small yellow clustered flowers. These are also native to Australia rather than Asia or the Caribbean and South-Central America like the Mimosa genus. Albizia julibrissin is a less used scent in perfume and cosmetics because it is very subtle many perfume alternatives are from the Acacia genus. The fragrance of A. julibrissin is made up of roughly 75 volatile compounds. Interestingly, some of these compounds are similar to the ones found in other plants that are also known for their strong aroma, such as citrus and coffee plants. Although I won't list all of the 75 compounds here, there are plenty of analyses available for those who wish to gain a more in-depth understanding of this topic.
Albizia julibrissin Wikimedia Andrew Butco 2006 Commons https://commons.wikimedia.org/wiki/File:Albizia_julibrissin_Ab-02.jpg
After examining some species and their components, it is apparent that there is still much to learn about each one, as well as others closely related. The Fabaceae family is a large and versatile one. With the advancement of scent analyses, we can now identify the specific chemical compounds emitted by plants, which reveal connections between different species. The primary evolutionary advantage of strong scents and volatile emissions is to attract pollinators during blooming time. However, when humans find novelty and purpose in plants, hybrid species and even invasive spread of plants are possible. Therefore, it is crucial to pay close attention to the types of plants you choose to grow if you want to create your own garden with delightful-smelling flowers.
Figure 7 Sweet pea by Dasha Horton 2023
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