The taxonomy of the genus Lavandula L

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Introduction

In the introduction to the Natural History of the Lavenders published in 1826 the author, Baron Gingins de la Sarraz, wrote 'continuing progress in the understanding of natural history would seem to require also a constant revision of families and genera most familiar to us'. While much progress has been made in our understanding of the genus Lavandula his sentiments are still true today. The genus is currently subject to ongoing research into its taxonomy and systematics being undertaken by the author and colleagues at the University of Cambridge, University of Reading and the Royal Botanic Gardens, Kew. This treatment thus represents a provisional rather than a definitive account on the taxonomy of the genus. While some aspects of the research is nearing completion there are still some problematic areas where existing treatments may not be adequate and our understanding of the taxonomy is incomplete and these are indicated and discussed where appropriate.

This treatment recognises thirty-two species of Lavandula which have been described in the literature plus a number of infraspecific taxa and hybrids, although the number of species is likely to be higher once all the revisionary work has been completed. The genus has a distribution stretching from the Canary Islands, Cape Verde Islands and Madeira, across the Mediterranean Basin, North Africa, South West Asia, the Arabian Peninsula and tropical NE Africa with a disjunction to India.

Some species have been widely cultivated since ancient times and are familiar garden plants and hence there are many legends and folklore associated with these plants. The essential oils, principally harvested from L. x intermedia and L. angustifolia, are of economic importance in the perfumery and fragrance industry, some are widely used in aromatherapy and are known to have antiseptic and antifungal qualities. A number of species and their hybrids are horticulturally desirable and are cultivated in both northern and southern hemispheres. The Latin name Lavandula comes from the ancient use of this plant to perfume water for bathing, being derived from the Latin word lavare, meaning to be washed.

Historical perspective: a brief history of the taxonomy of the genus

It is clear that Lavandula was known to the earliest botanical writers and the first written accounts of lavenders can be found in the writings of the early Greek scholars such as Theophrastus (c. 370—285 bc). The genus is frequently mentioned in many herbals and other botanical books although the first monograph of the genus, De Lavandula, was not published until 1780 (Lundmark, 1780). This work recognised five species and eight varieties.

The second monograph of the genus Histoire Naturelle des Lavandes (Gingins, 1826), was of great significance and is still a valuable work today. His monograph enumerated twelve species along with descriptions, geographical distributions, properties and uses. His most important contribution was the recognition of groupings of species within the genus and the erection of an infrageneric classification of three sections.

By the time of the third and most recent monograph, A Taxonomic Study of the Genus Lavandula (Chaytor, 1937), a substantial number of new species and varieties had been described and her revision bought much of this information together for the first time. This account recognises twenty-eight species plus many infraspecific taxa arranged in five sections. A new species, L. somaliensis, was described, many new combinations were made and a new section Subnuda was erected.

Since Chaytor's account there has been no full generic treatment although a number of useful accounts of various groups have been published. Collectively these works have contributed much to our knowledge of the genus and have been incorporated into this account. Some of the most notable works include, a revision of section Stoechas (Rozeira, 1949), the genus Lavandula in Arabia and tropical NE Africa (Miller, 1985) describing five new species from the area and on the taxa native to the Iberian Peninsula (Suarez-Cervera and Seoane-Camba, 1986, 1989).

Generic status and relationships

Lavandula is a member of the Lamiaceae (Labiatae) family and belongs to the subfamily Nepetoideae. Within the Nepetoideae a number of tribes are recognised and Lavandula is currently treated as a distinct and isolated group of its own, that is, the tribe Lavanduleae (Endl.) Boiss containing just the single genus Lavandula (Cantino et al., 1992).

What makes a lavender a lavender

The genus in terms of its general morphology is a rather mixed and divergent group. It is defined by the nectary lobes being opposite the ovary's rather than alternate (which is the case in all other Lamiaceae). The combination of a compact terminal spikes of flowers usually borne on a long peduncle (flower stalk); the declinate stamens (stamens curved downwards) borne within the corolla tube and persistent bracts are characteristic.

Many species are highly aromatic due to the presence of essential oils that are borne in glands covering much of the plant. In habit they vary from woody shrubs up to a metre in height, to perennial woody-based shrubs or annual herbs. The leaves can be entirely or deeply dissected, and are often absent in some of the Arabian species. The flowers (spike) consists of cymes, a branching determinate inflorescence with a flower at the end of each branch, either an opposite decussate arrangement (each pair of flower whorls at right angles to the pair above or below) or an alternate spiral arrangement. The cymes are subtended by bracts, which vary in their size, shape and nervation, which can be diagnostic for many species. The cymes can be single flowered usually without bracteoles or many flowered (3-9 flowers per cyme) with bracteoles. The bracte-oles are small, often minute, bracts borne at the points of branching within each flower whorl. In some species, such as L. stoechas and L. dentata, the bracts at the apex are enlarged, coloured and sterile and known as a coma. The calyx is (two-lipped) bilabiate and varies in the number of nerves, lobe shape, presence of an appendage, colour and provides many important characters used to diagnose both sections and species. The corolla is usually bilabiate, tubular and with five lobes varying in size, colour, shape and markings.

Taxonomic treatment

The species and infraspecific taxa are arranged according to sections. Those whose sectional position is uncertain are dealt with at the end. Hybrids have been dealt with under each section except for intersectional hybrids which are placed after the sections. Keys to the species are given under each section. Only the most important synonyms are given as appropriate for each species and placed in brackets as appropriate. Author abbreviations follow Brummitt & Powell (1992).

Sectional classification

Although the species exhibit a wide variation of morphological characters, it is evident that natural groupings of related taxa can be recognised. These groups have been classified as sections, of which there are six presently recognised. It seems likely that further groupings need to be recognised and current work is presently aiming to confirm this. The sections can be distinguished by differences in habit, leaf shape, the arrangement of the flowers in the verticils, bract, calyx and corolla characters (Figures 2.1-2.5).

Nomenclatural notes and clarification on sectional classification

The naming of all plants is governed by the International Code of Botanical Nomenclature which sets out a series of rules on the naming of plants. The code provides an internationally agreed set of rules and standards to which all names must comply to be accepted. While the code may require what appears to be some frustrating name changes it replaced a situation in which there was no agreed code and individuals constantly changed names to the greater confusion of everyone. Names will be stable when using this international standard once these changes and corrections have been made. In accordance with this code a number of changes have been made over recent years to the section names and hence it seems appropriate to explain and clarify these changes as follows:

1 Section Spica Ging. to section Lavandula — Article 22 of the code requires that the name of a subdivision of a genus that includes the type of the genus must repeat the name of the genus unaltered. The type concept is a central element of botanical nomenclature. Any name must have a type specimen (this is usually a herbarium specimen) which essentially acts as a permanent reference point that determines the application of that name. This rule allows the subdivision containing the type of the genus to be instantly identified. In the case of Lavandula the type of the genus is a specimen of L. spica L. (although the correct name in general usage is L. angustifolia). This type species was placed by Gingins (1826) in section Spica and hence the name of this section was changed to Lavandula so as to repeat generic name as required by Article 22.

2 The names of plants must also follow certain grammatic rules of botanical Latin, again defined in the code. In the case of section Subnuda and Dentata the names as originally published are incorrect according to Article 21.2 as this requires the epithet to be a plural adjective agreeing in gender with the generic name. In practice this requires the correction of the endings to Subnudae and Dentatae, respectively.

A bicincinnus cyme illustrating the branching pattern and position of bracteoles and bracts

Figure 2.2 Diagrammatic representations of the structure of the many-flowered (bicicinnus) and single-flowered cymes in Lavandula.

A single flowered cyme, with subtending bract

Figure 2.2 Diagrammatic representations of the structure of the many-flowered (bicicinnus) and single-flowered cymes in Lavandula.

Generic description

Lavandula L. (Synonyms — Stoechas Mill., Fabricia Adans., Chaetostachys Benth., Sabaudia Buscal. and Muschl., Isinia Rech. f.)

Shrubs, woody-based perennials or short-lived herbs; often aromatic, glabrous or with a variable indumentum. Leaves variable in shape, entire or dissected, sessile or petiolate. Inflorescence a congested terminal spike, occasionally with a coma, usually with distinct peduncle, simple or branched, verticils either a many-flowered (3-9) cyme with minute bracteoles or a reduced single-flowered cyme usually without bracteoles, subtended by persistent bracts variable in form, which maybe opposite or spirally arranged on the inflorescence axis. Calyx persistent, regular or two-lipped, upper with three-lobed, the lower two-lobed, ± equal in size or with the posterior lip larger or modified into an appendage, eight-, thirteen- or fifteen-nerved, the nerves in the lower sepals all borne to the apex. Corolla tube either just exceeding or up to 3 X longer

1. L. dentata var. dentatax160

2. L. viridis x160

3. L. latifolia x160

4. L. lanata x100

5. L. multifida x100

6. L. canariensisx100 7 . L. pubescensx100 8. L. tenuisectax100 9 . L. coronopifolia x100 10 . L. maroccanax100

11. L. aristibracteata x100

12. L. subnuda x160

13. L. bipinnata x100

14. L. atriplicifolia x100

Figure 2.3 Variation in corolla morphology within the genus Lavandula.

1. L. stoechas subsp. stoechasx250 4. L. multifidax160 7. L. subnudax 250

2. L. angustifolia x 250 5. L. mairei var. maireix 250 8. L. bipinnata x 250

3. L. dentata var. dentata x 160 6. L. pubescensx 250 9. L. hasikensisx 75

Figure 2.4 Examples of variation in the calyces within the genus Lavandula, illustrating differences in the calyx lobes.

than calyx, weakly or strongly two-lipped, upper lip with two lobes, the lower three-lobed, the lobes variable in size. Four stamens declinate (curving downwards), usually didynamous (two pairs of stamens unequal in length), the anterior pair longer, included within tube. Stigma single, bilobed or capitate. Nectary lobes borne opposite the ovaries. Nutlets variable in shape, colour and size, with either a small basal scar or lateral scar 0.25 - 0.75 X length of nutlet, mostly mucilaginous.

1. L. dentata var. dentata x100

2. L. viridisx60 (upper bract)

3. L. latifolia x160

4. L. multifidax160

5. L. canariensisx 250

6. L. maroccana x 250 7 . L. coronopifolia x 250 8. L. mairei var. maireix100 9 . L. aristibracteata x160 10 . L. subnuda x160

11. L. somaliensisx160

12. L. bipinnata x160

13. L. hasikensisx100

14. L. atriplicifoliax100

Figure 2.5 Examples illustrating the diversity of bract shapes in the genus Lavandula.

Synopsis of sectional classification and taxa recognised in this treatment

1. Section Lavandula ( — section Spica Ging.)

Section Pterostoechas (continued)

1. L. angustifolia Mill. subsp. angustifolia

12. L. maroccana Murb.

subsp. pyrenaica (DC) Guinea

13. L. tenuisecta Coss. ex. Ball

2. L. lanata Boiss.

14. L. maroccana Murb.

3. L. latifolia Medik.

15. L. mairei Humbert var. mairei

Hybrids

var. antiatlantica Maire

L. x intermedia Emeric. ex. Loisel.

16. L. antineae Maire

L. lanata Boiss. X L. angustifolia Mill.

17. L. coronopifolia Poir.

2. Section Dentatae Suarez-Cerv. &

18. L. pubescens Decne.

Seoane-Camba

19. L. citriodora A.G. Miller

4. L. dentata L. var. dentata

Hybrids

forma rosea Maire

L. x christiana Gattef. & Maire

forma albiflora Maire

L. x murbeckiana Emb. & Maire

L. dentata L. var. candicans Batt.

L. canariensis Mill. XL. buchii Webb &

3. Section Stoechas Ging.

Berthol. var. buchii

5. L. stoechas L. subsp. stoechas

5. Section Subnudae Chaytor

forma leucantha Ging.

20. L. subnuda Benth.

forma rosea Maire

21. L. macra Baker

subsp. pedunculata (Mill.) Samp. ex Rozeira

22. L. dhofarensis A.G. Miller

subsp. sampaiana Rozeira

subsp. dhofarensis

subsp. lusitanica (Chaytor) Rozeira

subsp. ayunensis A.G. Miller

subsp. luisieri (Rozeira) Rozeira

23. L. setifera T. Anderson

subsp. atlantica Braun-Blanq.

24. L. nimmoi Benth.

subsp. maderensis (Benth.) Rozeira

25. L. galgalloensis A.G. Miller

subsp. cariensis (Boiss.) Rozeira

26. L. aristibracteata A.G. Miller

6. L. viridis L'Hér.

27. L. somaliensis Chaytor

Hybrids

6. Section Chaetostachys Benth.

L. stoechas L. X L. viridis L'Hér.

28. L. gibsonii Grah.

4. Section Pterostoechas Ging.

29. L. bipinnata (Roth) Kuntze

7. L. multifida L.

Unclassified taxa

8. L. canariensis Mill.

30. L. hasikensis A.G. Miller

9. L. pinnata L. f.

31. L. atriplicifolia Benth.

10. L. buchii Webb & Berthel. var. buchii

32. L. erythreae (Chiov.) Cufud.

var. gracile M.C. León

Intersectional Hybrids

var. tolpidifolia (Svent.) M.C. León

L. x allardii Hy

11. L. minutolii Bolle var. minutolii

L. x heterophylla Poir.

var. tenuipinna Svent.

L. dentata L. X L. lanata Boiss.

Key to sections

1 Cymes 3-9 flowered; nutlets with a basal scar only 2

Cymes single-flowered; nutlets with a lateral scar 4

2 Leaves and calyx sessile, stigma capitate Section Stoechas

Leaves and calyx with short stalk, stigma bilobed 3

3 Leaves with regular shallow dissections, corolla lobes subequal in size, corolla tube just exerted from calyx, calyx appendage c. 1.5 X width of the calyx Section Dentatae

Leaves simple and entire, corolla lobes differing in size, corolla tube c. 2 X length of the calyx, calyx appendage the same width as the calyx Section Lavandula

4 Leaves ovate lanceolate in outline, dissected or lobed; calyx zygomorphic (bilaterally symmetrical); corolla violet blue or white, strongly zygomorphic 5

Leaves linear and simple, calyx regular and lobes all equal; corolla yellow . . . . L. atriplicifolia/ brown in colour, with equal lobes, star shaped L. erythrae

5 Cymes and bracts arranged in an opposite and decussate fashion, spike 4-seriate (quadrate) to biseriate in shape Section Pterostoechas

Cymes and bracts arranged in an alternate, spiral fashion.

Spike cylindrical or head like (capitate) in shape 6

6 Spikes elongated, leaves pinnatifid or bipinnatisect, bracts ovate spinescent 7

Spike capitate, leaves lobed, bracts with orbicular wings L. hasikensis

7 Leaves predominantly pinnatifid to bipinnatisect, suffruticose shrubs, lateral scar on nutlets c. 0.25 X the length of nutlet. Lower corolla lip about the same size as lateral corolla lobes Section Subnudae

Leaves very distinctly bipinnatisect, plant herbaceous, lateral scar on nutlets c. 0.75 X length of nutlet. Lower corolla lip larger than lateral lobes Section Chaetostachys

Section 1: Lavandula (—Spica Ging.)

Woody shrubs with simple leaves generally linear in shape. Cymes borne in an opposite and decussate arrangement. Each cyme many-flowered (3-)5-7(-9) with bracteoles present, the subtending bracts variable in shape with reticulate veining. Calyx tubular with a very short stalk (pedicellate), with thirteen or eight nerves, the upper middle lobe modified into a circular appendage. The corolla tube exerted from the calyx, the upper corolla lobes larger than the lateral lobes. Stigma bilobed. Nutlets bear a small to minute basal scar and produce no mucilage on wetting.

Contains three species from central and south west Europe. Commercially this is the most important section containing, L. angustifolia (English lavender) and the hybrid L. x intermedia (lavandin), which are the principal taxa cultivated for the production of essential oils and widely grown for their horticultural value. Numerous cultivars of L. angustifolia and L. x intermedia have been and continue to be selected both for oil production and ornamental value. There is no complete listing of cultivars but the following references provide useful information: Tucker and Hensen (1985); Andrews (1994); McNaughton (2000).

One of the greatest confusions in the naming of lavenders has occurred over the application of the name L. spica (see Green, 1932). The Swedish botanist Carl Linnaeus first used the name

L. spica, to included both lavender (L. angustifolia) as his L. spica var. a and spike lavender (L. latifolia) as his L. spica var. ¡3. Unfortunately, subsequent authors who recognised these taxa as distinct species where not consistent in the use of the name and L. Spica has variously been applied to both L. angustifolia and L. latifolia. With no consistency in the use of this name the situation became completely confused and hence the use of the name L. spica was abandoned, the next available name being L. angustifolia Miller.

Key to species and major hybrids

1 Bracts subtending flowers ovate rhombic (diamond shape) 2

Bracts subtending flowers linear to linear-lanceolate in shape 4

2 Bracts at least twice as broad as long, bracteoles minute

(not clearly visible) L. angustifolia

Bracts c. 3 X longer than broad, bracteoles large 1—4 mm 3

3 Flower stalks usually unbranched, flowers deep purple/mauve in colour,

L. leaves with woolly grey to silver indumentum L. angustifolia X L. lanata

Flower stalks branched, shades of purple lilac, blues or white, leaves with non-woolly grey to silver grey indumentum L. x intermedia

4 Calyx with eight nerves and eight-toothed. Leaves with uniform dense white woolly indumentum L. lanata

Calyx with thirteen nerves and five-toothed. Leaves with silvery—grey indumentum L. latifolia

1. L. angustifolia Miller subsp. angustifolia (L. spica L. var. a, L. officinalis Chaix, L. fragrans Jord., L. vera DC)

Shrub to 50 cm with linear-lanceolate leaves grey tomentose when young, becoming greener with age. Inflorescence stalk usually unbranched 10-25cm long with a compact spike 4—5(—8)cm, sometimes with a lower flower cluster distant from the main spike. Bracts broadly ovate-rhombic to obovate, bracteoles present but minute. Calyx thirteen-nerved, with small circular appendage. Corolla strongly bilaterally symmetrical, nearly twice the length of calyx with prominent lobes, shades of blue/mauve, white, rarely violet pink in colour. Flowers from mid-June to July. Native to SW and South Central Europe (Italy, France and Spain) in mountainous areas usually over 1500 m, but widely cultivated and sometimes naturalised elsewhere. The natural variation in this species across its range is not fully understood and there are many names in the literature. While only two subspecies are listed here this reflects that these are the only two whose delimitations and identification are clearly understood. Further work may identify other infraspecific taxa. This species produces the best quality oils and is a fine ornamental plant. Its mountain origins make this the hardiest species in cultivation. Of the many cultivars the following are some of the best known, for example, 'Hidcote' 30 cm very deep violet blue flowers (Figure 2.6), 'Loddon Blue' 60 cm dark violet blue, 'Munstead' 45 cm blue lilac flowers, 'Rosea' 45 cm pink flowers, 'Nana Alba' 20 cm dwarf white variant.

L. angustifolia Miller subsp. pyrenaica (DC) Guinea — a variant from the East Pyrenees and NE Spain which has larger floral bracts which usually exceed calyx in length, a shorter and more condensed spike, deep blue/purple flowers and is of smaller stature (25-35 cm).

2. L. latifolia Medik (L. spica L. var. 3; L. latifolia Villers)

Shrub 50-70 (100) cm. Leaves grey, linear-lanceolate to spathulate in outline. Inflorescence stalk distinctly branched usually forming a trident shaped flower spike, up to 25 cm high. Spike often

Figure 2.6 L. angustifolia 'Hidcote' — cultivated at Cambridge University Botanic Garden. (See Color Plate I.)

interrupted, 5-8 cm long. Bracts subtending cymes linear-lanceolate in shape, Bracteoles distinct to 4 mm long. Calyx thirteen-nerved, with rotund appendage. Corolla strongly bilaterally symmetrical, blue to mauve in colour. Flowers from mid-July. Native to SW and South Central Europe to c. 1000 m (—1200 m) (Figure 2.7).

Only occasionally cultivated both for its oil, which is of low quality and as an ornamental.

Shrub 50-80 cm, both stems and leaves covered with dense short white woolly indumentum of branching hairs. Leaves linear to oblanceolate (tapering towards the base). Inflorescence stalk often branched to 25 cm, spike often interrupted to 8 cm long. Fertile bracts linear-lanceolate bracteoles up to 6 mm in length, calyx eight-nerved with eight lobes (four large distinct lobes alternating with four smaller lobes) with elliptic to rotund appendage. Corolla rather small exceeding calyx by only 2-3 mm, the upper lobes only slightly larger than the lower lobes, dark purple. Flowers mid-to late July. Native to mountainous areas in South Spain over 2000 m.

Sectional hybrids

L. x intermedia Emeric ex Loisel. (L. angustifolia X L. latifolia) (L. hybrida Reverchon; L. x hortensis Hy)

A vigorous shrub from 60-150 cm, highly variable making delimitation difficult at times. Leaves linear-lanceolate to spathulate, often grey tomentose. Inflorescence stalk branched, spike usually lax and occasionally interrupted. Fertile bracts ovate-rhombic in outline but variable in

Figure 2.7 L. latifolia — France, Col de Ferrier nr. Grasse. View of flower spike showing linear bracts and bracteoles. (See Color Plate II.)

exact shape and size, bracteoles 1—4 mm long. Calyx thirteen-nerved, with rotund to elliptic appendage. Corolla bilaterally symmetrical, variable in colour usually shades of lilac-purple to white. Flowers from late June to July.

A natural sterile hybrid occurring in Spain, France and Italy where the two parents meet. Commonly known as lavandin with numerous cultivars selected for oil production and horticultural purposes, for example, 'Alba' to 100 cm white flowered, Dutch Group 80 cm pale blue-violet flowers and grey leaves, 'Grappenhall' 90 cm lilac-purple flowers, green foliage, 'Grosso' 75 cm with a profusion of dark violet-blue flowers (the most popular lavender for oil production) (Figure 2.8), 'Hidcote Giant' 90 cm with stout spikes of violet-blue flowers, 'Lullingstone Castle' 100 cm dark blue-violet, grey leaves, ' Old English' 100 cm violet flowers, grey-green foliage, 'Seal' vigorous to over 100 cm, violet-blue flowers.

L. lanata Boiss. X L. angustifolia Mill

Similar to L. lanata in general habit 60—70 cm tall with grey to silver-grey leaves. Flower spike with purple flowers, bracts subtending the whorls narrowly rhombic (diamond) in shape, about 3 X longer than broad. Flowers violet purple. Flowers mid-June to July.

Several hybrids of this parentage are in cultivation and make fine ornamental garden plants that tend to be more robust in cultivation than L. lanata. Cultivars include: 'Richard Gray' — to 60 cm with rounded flower spikes and 'Sawyers' - taller form to 70 cm with large conical flower spikes, both of UK origin; 'Silver Frost' — to 50 cm with conical spikes raised in the United States; 'Joan Head' — 60—70 cm with cylindrical spikes raised in New Zealand.

Figure 2.8 L. x intermedia 'Grosso' — cultivated at Norfolk Lavender, UK. The most widely cultivated lavandin for oil production. (See Color Plate III.)

Section 2: Dentatae Suarez-Cerv. and Seoane-Camba

Woody shrub with distinctive leaves, linear-lanceolate in shape with regular shallow-rounded lobes. Flower spike compact and dense, topped by a tuft of enlarged and coloured sterile floral bracts (a coma). The fertile bracts broadly obovate with an acute apex, with reticulate veining. Flower whorls 5—7(—9) flowered with minute bracteoles. Calyx with a short stalk (pedicellate), thirteen-nerved, the middle calyx lobe modified into a large appendage up to 1.5 X the width of calyx tube. Corolla tube only slightly exerted from calyx c. 2 mm. Stigma bilobed. Nutlets elliptic in shape with a minute basal scar producing mucilage on wetting.

Contains a single species, L. dentata, recognised in this treatment with two varieties and two forms. This species has an interesting distribution being native to South Spain and Balearic Islands, western North Africa (Morocco, Algeria, Tunisia) with a disjunction to the SW Arabian Peninsula (Saudi Arabia and Yemen Arab Republic) and Ethiopia (Abyssinian Highlands). It is naturalised in Portugal and Corsica and widely cultivated elsewhere principally as an ornamental in frost free areas as it is not reliably hardy below 0°C.

L. dentata was previously placed in section Stoechas, where its position has always been rather anomalous. This was commented on by Chaytor (1937) and first taxonomically recognised by Rozeira (1949), who created a separate subsection Dentata, for this species within section Stoechas. A new section Dentata (=Dentatae), was created by Suarez-Cervera and Seoane-Camba (1986), to accommodate L. dentata. Its affinities also appear to lie closer to section Lavandula rather than section Stoechas.

Figure 2.9 L. dentata var. dentata — Morocco. (See Color Plate IV.)

4. L. dentata L. var. dentata (L. santolinaefolia Spach)

An aromatic woody shrub, 50—100 cm, with an indumentum variable in density giving plants a green to grey-green appearance. Flower spike 3-6 cm, the coma consisting of enlarged sterile floral bracts, rhombic in shape, violet-blue in colour, grading down to fully fertile non-modified bracts (Figure 2.9). Corolla principally shades of violet-blue to mauve. Variants with pink or rose flowers and bracts should be treated as forma rosea Maire, those with white flowers forma albiflora Maire.

A number of cultivars have been selected including 'Royal Crown' — to 75 cm green foliage and pale violet-blue flowers, 'Linda Ligon' — to 60 cm variegated foliage selected in the United States, 'Ploughmans Blue' — to 75 cm green foliage and pale violet-blue flowers selected in New Zealand.

var. candicans Batt. (silver form) — is easily distinguished by almost all parts being white tomentose. Occurs as distinct populations throughout the range of var. dentata.

Section 3: Stoechas Ging.

A distinct group of small woody shrubs with linear-lanceolate leaves. Diagnosed by their corolla lobes that are all similar in size, the corolla tube only just exerted from the calyx, the broad ovate to slightly obovate bracts and the capitate stigma, unique to this section. The flower spike is dense and compact, each whorl of flowers (3—)5—7 flowered, minute bracteoles present. Apex of spike topped by a distinctive tuft of enlarged and coloured sterile floral bracts (a coma). The coma differs from L. dentata (the only other taxon bearing a coma) in being fully sterile and by the shape of the bracts, which are linear lanceolate. Some of the earliest lavenders to flower from late spring. The epithet Stoechas is derived from the Stoechades Islands situated off southern France (now known as the Iles de Hyeres) from were the plant was first described by the Greek physician Dioscorides.

Section Stoechas, as circumscribed here contains just two species L. stoechas and L. viridis. This hides the great diversity of taxa and variation that exists within this section as a multitude of infraspecific taxa are recognised under L. stoechas. It is these taxa whose identity and true relationships remain both problematic and elusive. At present there is no completely satisfactory treatment for the whole section and hence further research is being undertaken to address these questions. The treatment given here is provisional and follows the most frequently used classification purely for stability. Hence, no key is given to the subspecies of L. stoechas as the characters used to distinguish them are presently not fully understood and tested. A useful treatment of the Spanish and Portuguese taxa is given in Suarez-Cervera and Seoane-Camba

5. L. stoechas L. subsp. stoechas

Shrub 40—70 cm. Leaves often grey tomentose. Inflorescence stalk sessile or no longer than length of spike. Apex topped by enlarged sterile floral bracts obovate or spathulate 1-2 (4) cm long (Figure 2.10). Fertile bracts broadly ovate to obovate, shortly acuminate. Calyx sessile, thirteen-nerved the middle lobe of calyx modified into an appendage. Corolla black-purple to mauve in colour, white variants being named var. leucantha Ging. and rose red or pink flowered variants forma rosea Maire. Widespread throughout the Mediterranean basin and often a common element of maquis and garrigue type vegetation on acid substrates.

Grown for the extraction of essential oils on a small scale mainly in Spain for use in air fresheners and deodorants. Widely cultivated as an ornamental shrub and sometimes naturalised. A number of cultivars have been named including, 'Snowman' — white flowers and coma to 45 cm and 'Kew Red' — rosy pink flowers and coma to 45 cm. It is now classed as an invasive weed in parts of Australia where its cultivation is strictly controlled. Commonly referred to as French or Italian lavender.

Subspecies

Subsp. pedunculata Miller (Samp. ex Rozeira)

Bears distinctive erect branches and long narrow lanceolate leaves. Flower stalk (peduncle) long (10—)20—30 cm, spike usually quite short 2—3 cm, ovate in outline. Lower fertile bracts kidney shaped, the upper fertile bracts broadly obovate. Coma large 3—4 cm and narrowly lanceolate to spathulate in shape. Calyx appendage ± entire. Spain and Portugal on calcareous soils.

A number of cultivars have been named of which the most commonly available is 'James Compton'.

Key to species

Plant with green sterile bracts, leaves very glandular and sticky (viscid) Plant with coloured sterile bracts, leaves not sticky

L. viridis

L. stoechas and subsp.

Figure 2.10 L. stoechas subsp. stoechas. (See Color Plate V.) Subsp. sampaiana Rozeira

Flower spikes large and robust, twice as long as broad. Lower fertile bracts almost circular, the upper fertile bracts obovate. Coma linear obovate in shape. Calyx appendage ± entire. Western Spain, North and Central Portugal.

Subsp. lusitanica (Chaytor) Rozeira

Flower spikes relatively small, not much longer than wide, ovate in shape. Lower fertile bracts kidney shaped, the upper fertile bracts broadly obovate. Coma small, linear obovate in shape. Calyx appendage ± entire. Southern Spain and Portugal.

Subsp. luisieri (Rozeira) Rozeira

Flower spike large and robust, twice as long as wide borne on a relatively short peduncle c. 4—8 cm long. Basal fertile bracts almost circular, the upper fertile bracts diamond shaped. The stems appear very erect in form. The coma large, ovate-lanceolate in shape. Calyx appendage ± entire. South West Spain, Central and Southern Portugal.

Subsp. atlantica Braun-Blanq.

A compact shrub with a robust conical spike borne on a peduncle to c. 10 cm. Calyx appendage large exceeding width of calyx tube. Basal fertile bracts almost circular, the upper bracts broadly obovate and truncate. Coma large up to 4 cm, spathulate in shape. Calyx appendage lobed. Morocco over 1000 m.

Subsp. maderensis (Benth.) Rozeira

The peduncles are highly variable in length from 3.5 to 13 cm. Lower fertile bracts kidney shaped. The coma small c. 2 cm long and spathulate in shape. Madeira.

Subsp. cariensis (Boiss.) Rozeira

Peduncles long up to 20 cm. Lower fertile bracts broadly obovate. Coma narrowly oblong in shape. Calyx appendage lobed. Turkey (European Turkey and W. Anatolia) on acidic soils.

Shrub to 30—50 cm, leaves broadly linear-lanceolate, green foliage with a distinctive dense glandular indumentum giving a sticky feel with a strong smell similar to lemons. Inflorescence spike up to 8 cm. Coma broadly ovate, fairly short 2—3 cm and green. Fertile bracts obovate or broadly ovate greenish-white in colour. Flowers white borne over a long period in cultivation. Native to SW Spain and South Portugal in open maquis at fairly low altitudes and Madeira.

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  • kathrin
    What plants have the genus lavandula?
    1 year ago

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