Lavender - What a Genus!
The genus belongs to the Lamiaceae (or Labiatae) family. Commonly referred to as the Mint Family. For the botanists amongst us the family is a member of the Division; Magnoliophyta. class; Magnoliopsida, the order; Lamiales. The family consists of more than 180 genera and 3500 species. These are from all parts of the world with the greatest number coming from the Mediterranean. There are several genera in Australia, with the most widely known being Westringia (the native Rosemary) and Prostanthera (the native Mint Bush). Some of the major non Australian genera are; Teucrium, Salvia, Mentha, Origanum, Thymus and Rosemarinus.
Lamiaceae includes plants that are of some economic importance around the world as sources or aromatic oils and for their culinary uses. The majority are aromatic shrubs. The stems are often quadrangular with simple, opposite or occasionally whorled leaves. The flowers are usually bisexual in axillary clusters.
Lavender is a popular genus in Australia with thousands if not a million plus plants sold each year. They are popular as garden plants and there is also a slowly building commercial lavender industry. Until the mid nineties the only real way to import lavender was by seed as AQIS treatments were proving fatal to the new plants. This has caused a lot of variation within ‘new’ varieties. There is also a lot of confusion in the naming of plants plus quite a few incorrectly named species and varieties.
With the ornamental forms these problems are annoying but not critical. With the commercial forms they are a major issue. There was and still is confusion between Lavandula angustifolia and Lavandula x intermedia – as different as red and white wine to an oil producer. The actual cultivars can also significant difference in oil content that will only show up when the plants are three years old and in full production – and expensive error.
The Romans are credited with giving the name Lavender. It is generally believed that the word is a derivation of the latin verb lavare, which means to bathe. The species first described is Lavandula stoechas from the Stoechades Islands (now called Iles de Hyeres). The Greeks and Romans also referred to lavender as Nard, from the latin Nardus italica, after the Syrian town Naarda.
The botanic descriptions of the various forms of Lavender dates back to the Middle Ages. They were so prevalent in the life of herbalists, scientists and common folk that they appeared in many of the very early books. The genus was reviewed many times but it wasn’t until the review by Tim Upson and Sysn Andrews that the genus was finally understood. Susyn and Tim visited all the major growing regions across the world. They collected specimens, read texts, spoke with breeders and collectors and examined thousands of preserved specimens.
The genus Lavandula is divided in to three subgenera: Lavandula, Fabricia and Sabaudia. These are in turn divided into eight sections: Stoechas, Dentatae, Lavandula in subgenus Lavandula, Ptereostoechas, Hasikensis, Subnudae and Chaetostachys in subgenus Fabricia and Sabaudia in subgenus Sabaudia.
Subgenus Sabaudia consists of two distinct species from North Eastern Africa and the Arabian Peninsula. They are rare in cultivation and unlikley to be present in Australia. The flowers are buff yellow and star shaped. The two species are L. atriplicifolia and L. erythraeae.
Subgenus Fabricia covers species from the Macaronesia (five groups of islands in the Atlantic west of Gibraltar) right across the Mediterranean, the Middle east and across to India. Section Chaetostachys covers two species from India. Sections Sunudae and Hasikensis have 12 species between them with only a couple grown here in Australia in very small quantities.
Section Pterostoechas is the largest of the whole genus and refers to the commonly called Fernleaf Lavenders. Of the 16 species five are in common cultivation here in Australia. It includes the species L. canariensis and its seven sub species, L. multifida, L. pinnata and L. buchii (the correct name for the plant we call L. pinnata).
The subgenus of most concern to the trade is Lavandula. It includes the three sections that produce all the commercial oil forms, all the cut flower forms and most of the ornamental and pot varieties.
Section Dentatae has one species and two varieties: L. dentata var dentata and L. dentata var candicans. The latter is the more silvery grey form that has been grown here since the late nineteenth century. It is commonly called French Lavender. L. d. dentata has grey green foliage and only found its way to Australia in the late twentieth century. Both varieties are medium sized shrubs with dentate leaves that perfrom well in the drier parts of the country. There are many cultivars and include plants like: ‘Ploughman’s Blue’ ‘Pure Harmony’, Mt Lofty Lavender, ‘Linda Ligon’ and ‘Royal Crown’.
Section Stoechas only has three species: L. viridis (green lavender), L. stoechas (Italian Lavender here and French Lavender in Europe) and L. pedunculata (Spanish) however it has many sup-species and hundreds of cultivars. In several parts of Australia the type (L. stoechas ssp stoechas) is classified as a weed. It seeds quite profusely although the weediness is confined to areas that typify its natural growing environment. It is basically a coloniser and requires bare or exposed ground to get a hold. It is the ease with which it and L. pedunculata seed that has generated so many cultivars.
Originally all three species were classsed as one with L. stoechas being the earliest of all lavenders to be used and described. Indeed there are recorded uses of it in the centuries BC. The early records of the Ancient Greeks, Romans and Arabs show regular usage of Lavender. It was used as a medicine, a bathing additive and a body perfume along with numerous ‘new age’ type uses with more folklore than legitimate fact as the foundation.
There are two subspecies with three forms of Lavandula stoechas: L. s. ssp stoechas f . stoechas, L. s. ssp stoechas f . leucantha (white), L. s. ssp stoechas f .rosea (pink) and L. s. ssp luisieri (Portugese Lavender). There are many cultivars of these forms with a dazzling array of colors. They charateristically have colored bracts (or wings) at the top of the flower heads. They are generally short and deeply colored. The flower heads have short peduncles and the plants are usually between 30 and 50 cm.
Lavandula viridis is one of the ‘non-lavender’ lavenders. The species is charaterised by a strong menthol like fragrance and lime green flowers. There are a couple of cultivars with flowers varying from yellow green to white. It is also one of the parents in several popular crosses.
The third species is Lavandula pedunculata and is probably the parent of some of the most eye catching lavenders. Plants like Lavandula ‘Avonview’ and Lavandula ‘Ploughman’s Purple’ make a stunning show and are some of the most popular and attractive lavenders on the market. This species has long peduncles with as much as 25 cm between the foliage and the flower heads. It also has the sterile bracts atop the flower heads but they are much larger and there is often more than four of them. There are five subspecies including L. pedunculata sampaiana which is grown in Australia as Sampan Lavender.
The final section is Lavandula and it is by far the most important. Indeed it is the products from plants in this section that have given lavender its world wide allure. Again there are only a few species with two sub-species, four hybrids and hundreds of cultivars. The three species are L. angustifolia, L. lanata and L. latifolia. One of the hybrids, L. x intermedia is natural occuring and a major horticultural crop, one is of garden origin with a dozen or so cultivars and the other two are virtually unknown.
All the forms have narrow, lanceolate leaves with enitire margins. The flowerheads are borne atop long slender peduncles. Most of them have small florets arranged in whorls in long flower spikes with oil sacks at the base of each floret. It is these oil sacks that are why lavender is grown in such large quantities and it is the composition of that oil that determines the value of the plant.
Lavandula lanata (Woolly Lavender) is an attractive shrub but not widely grown. It is not used for oil or stripping but is occasionally used for fresh flower production. It is the parent for garden origin hybrid Lavandula x chaytorae.
Lavandula latifolia in itself is not a hugely popular plant. It has a strong. Camphoraceous oil with significant branching of the flower stem This gives the plant an untidy appearance. The leaves are somewhat larger than L. angustifolia. The flowerhead is quite long, often up to 15cm, cone shaped and can be well segmented. It’s real siginificance is as one of the parents of Lavandula x allardii, Lavandula x heterophylla and Lavandula x intermedia. It occurs in southern France at altitudes of less than 1000m.
Lavandula angustifolia is the prime lavender. It is the source of all the culinary and premium perfume oils. The oil is generally low in the camphoraceous components and has a sweet fragrance. It has short peduncles with short ‘stumpy’ flower heads. Flower size varies from 1cm on plants like Lavandula angustifolia ‘Lady’ to 6cm on Lavandula angustifolia ‘Riverina Heather’. It is known as the True English Lavender. It naturally occurs in southern France at altitudes above 1000 m. There are over 100 cultivars of this species. Some were selected for their floral qualities, some as pot and ornamental garden plants and many for the composition or yield of the oil.
The last variety of importance is Lavandula x intermedia (Lavandin) which is the naturally occuring hybrid between L. latifolia and L. angustifolia. The hybrid is sterile (due to an odd chromosome number) but there are still a significant number of cultivars. This plant yields much greater volumes of oil than L. angustifolia but is much higher in the camphoraceus components. It is used in aromatherapy, cleaning products and for stripping.
Finally there is some work being done with polyploidy. This is done by treating plants with certain chemicals that can cause a doubling of the chromosome number. This can increase the size of the plant or specific parts of the plant. In the case of Lavandula x intermedia the doubling gives an even chromosome number which will allow the breeding and thus varietal selection. Larkman Nurseries undertook a breeding program with Charles Sturt University to do this. From the program several selections and back crosses have been made. There are triploid forms of Lavandula x intermedia, tetrapolid forms of Lavandula angustifolia and a new form of Lavandula x heterophylla. These will be released as the ‘Riverina Series’.
This is a brief summary of the genus Lavandula. As can be seen it is a much more complex and broad ranging genus than what we have seen here in Australia. If you are interested in furthering your knowledge then there are two books that are a must:
The Genus Lavandula by Tim Upson and Susyn Andrews
Lavender: The Grower’s Guide by Virginia McNaughton
References: The Genus Lavandula – Upson & Andrews, Lavender: The Grower’s Duide – McNaughton, The Essential Lavender – McNaughton, Lavender Sweet Lavender – McLeod, Lavender Oil – Lawless, Lavender – Platt, The Lavender Garden – Kourik, Lavandes ou Paysages de Lavande – Couttolenc, Lavender, the most essential oil – Haas, Lavender, The genus Lavandula – Balchin, Lavender Country of Provence – Silvester, Lavender, a growers guide for commercial production – McGimpsey and Porter, Norfolk Lavender, A family business – Head Family