Labiatae

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Labiatae

Description

Unarmed, erect, mostly aromatic (sometimes fetid-aromatic) herbs, sometimes woody at the base; Leaves decussate, rarely whorled, mostly simple, rarely lobed or pinnate, exstipu-late. Stamens usually 4 and didynamous, inserted on the corolla tube, sometimes the upper (posterior) pair imperfect, rarely the lower pair barren (Mosla), filaments sometimes hairy, rarely connate at base; Ovary superior, consisting of 2 carpels, each of which is 2-celled by intrusion of the ovary wall. Ovules solitary, anatropous. Fruit consisting of 4 dry or rarely fleshy (Gomphostemma), 1-seeded schizocarpous nutlets which remain enclosed in the persistent calyx; Seed small, erect or ± transverse (Scutellaria), ± exalbuminous;

Distribution

Africa: present Asia: present Asia-Tropical:, Borneopresent; Indiapresent; Jawa (Jawapresent); Malayapresent; New Guineapresent; Philippines (Philippinespresent); Sulawesi (Sulawesipresent); Sumatera (Sumaterapresent) Australasia:, Tasmania (Tasmaniapresent) Continental SE. Asia: present Cosmopolitan: present E. Java: present East Java: present East Malesia: present Lesser Sunda Is: present N. Philippines: present North Malesia: present Pacific:, Hawaiipresent Pacific Islands: present S. Celebes: present SE. Asia: present South Malesia: present Southern America: Sumba: present Timor: present Upper Burma: present West Java: present West Malesia: present driest part of E. Java near Asem Bagus: present islands of Malesia: present the Mediterranean region: present
Cosmopolitan, with c. 180 genera and over 3000 spp., highly developed in the Mediterranean region; certain groups confined to distinct parts of the world, e.g. the (woody) Prostantheroideae in Australia and Tasmania, and Catopherioideae in Central America.
All native genera belong either to the group of 12 (African-) Indo-Australian genera: Ajuga, Anisomeles, Basilicum, Ceratanthus, Leucas, Mentha, Ocimum, Plectranthus s.l., Pogostemon s.l., Salvia, Scutellaria, Teucrium, or to the group of 16 Indo-Malesian genera which do not occur in Australia: Achyrospermum, Acrocephalus, Cymaria, Elsholtzia, Eurysolen, Gomphostemma, Melissa, Mesona, Microtoena, Mosla, Nosema, Orthosiphon, Paraphlomis, Platostoma, Satureja, Stachys. Several of the last group extend with their species to New Guinea however, e.g. Acrocephalus, Cymaria, Microtoena, Orthosiphon, Satureja.
The other genera of this group extend to West Malesia only, sometimes including Celebes. Their species may have a restricted occurrence in West Malesia, being confined e.g. to Malaya: Gomphostemma crinitum, to Sumatra: Elsholtzia blanda, Mosla dianthera, and Teucrium quadri-farium, to Java: Stachys oblongifolia, Platostoma africanum, to Sumba, or occupy only South Malesia (Sumatra, Java, sometimes also Lesser Sunda Is.): Gomphostemma parviflorum, Melissa axillaris, and Nosema cochinchinense, or North Malesia (the Philippines): Salvia scapiformis, Mosla formosana.
Reversely, none of the genera endemic to Australia have radiated into Malesia, though a few Australian species of wider generic area do extend to East Malesia, viz Ceratanthus longicornis, Plectranthus conges tus, P. parviflorus, and Teucrium corymbosum.
As Labiatae are largely developed in dry regions of the globe it is not astonishing that there is only one endemic genus in Malesia, viz Acrymia, a monotypic genus confined to ancient limestone hills in Malaya.
At species level there are, however, an unexpected large number of endemic Malesian species, namely 16. Half of them occur in more than one island or island group, viz Achyrospermum densiflorum, Elsholtzia pubescens, Gomphostemma curtisii, G. microcalyx, Paraphlomis oblongi-folia, Plectranthus galeatus, P. javanicus, and Scutellaria javanica.
Others have a narrower range and could be called local-endemics, being restricted to one island or island group; they are: Gomphostemma dolichobotrys, Plectranthus apoensis, P. merrillii, P. petraeus, P. steenisii, Pogostemon philippinensis, P. reticulatus, and P. velatus. The distribution of these endemic species over the islands of Malesia gives quite a different pattern from what is usual in other genera of forest plants, where endemics mostly center in New Guinea, the Philippines, Borneo, and Malaya.
Among the non-endemic species a few show considerable disjunctions (gaps) in their range, e.g. Leucas marrubioides: Asia — East Java, Stachys oblongifolia: SE. Asia — West Java, Platostoma africanum: Africa — India — Sumba, as well as the genus Ceratanthus which occurs in continental SE. Asia and then again in New Guinea.
One would expect quite some Labiatae in the category of disjunct drought plants, effected by the seasonal drought of the monsoons, as explained by VAN STEENIS (), because Labiatae have a tendency towards development in dry hot climates. There are indeed some lowland species which show this disjunct pattern which is defined by a strong or rather strong dry season (classes 4 and 5), viz: Cymaria elongata which occurs in India and then in Timor, Cymaria dichotoma known from SE. Asia and E. Java, S. Celebes, and N. Philippines, Gomphostemma hemsleyanum occurring in Upper Burma and then in the driest part of E. Java near Asem Bagus, Platostoma africanum found in India and Sumba, and Orthosiphon thymiflorus from SE. Asia and E. Java. There are some others, e.g. Leucas marrubioides which show a similar disjunction between SE. Asia and East Java, but this plant is little affected by the dry season, as it grows in East Java at 2000-2400 m altitude, and is thus less restricted in area by drought.
Malesian Labiatae show also a relation with those of the Pacific Islands, where this family is poorly represented, except in Hawaii, where there are 3 endemic genera of which some possess several species, viz Haplostachys, Phyllostegia, and Stenogyne. It is interesting that they are in part climbing and furthermore that they possess drupaceous fruits. According to BRIQUET (1895) they are allied to the Indo-Malesian genus Gomphostemma which shares this fruit character.

Pollination

Malesian Labiatae are generally pollinated by bees and bumblebees; there are no native representatives with long vividly coloured flowers to attract honey birds. It has, however, been described from the introduced Leonotis nepetaefolia by W. M. DOCTERS VAN LEEUWEN (), who observed flower visits by the honey bird Cinnuris pectoralis HORSF.; for the rest he remarked that it is homogamous so that self-pollination is not excluded.

On flowers of Anisomeles, Leucas and Salvia he observed not bees or bumblebees but only Xylocopa. This was also observed by HEIDE for Plectranthus tuberosus in Java ().

Further DOCTORS VAN LEEUWEN remarked that the small and narrow-flowered Labiatae, as e.g. Mentha and Thymus are visited by syrphids.

Protandry is a common phenomenon in Labiatae.

Cleistogamous flowers occur for instance in Orthosiphon aristatus: BACKER & BAKHUIZEN VAN DEN BRINK Jr () recorded that they are not rarely occurring, in which case the corolla is hidden in the calyx base; stamens are very short, the style is tortuous; ovary and nutlets, are, however, normal. Normally Orthosiphon is pollinated by butterflies ().

Ocimum gratissimum is visited by bees for its nectar; it has ultimately self-pollination.

Plectranthus javanicus is regularly visited in Java by Bombus rufipes (); Elsholtzia pubescens attracts by its honey-scented flowers swarms of bees in East Java.

In India Ajuga bracteosa is exclusively visited by day-time sphingids.

Dispersal

No special mechanisms are known for the dispersal in nature of the dry nutlets in Malesia. In Gomphostemma the white pericarp is fleshy, but anyway the nutlets remain concealed in a fairly large calyx. In some Labiatae the calyx teeth are bent inward more or less prohibiting the nutlets falling out and in such cases the calyx may act as a diaspore. In Ocimum and some other genera the pericarp swells and becomes gelatinous in contact with water.

Taxonomy

Within the Tubiflorae the Labiatae are closest related with the Verbenaceae and the distinction between these two families rests on rather arbitrary grounds, as pointed out by BRIQUET in his admirable treatment in . He clearly explained that the traditional main distinction between these two families, viz a terminal style in Verbenaceae and a gynobasic one in Labiatae is not tenable. JUNELL () has later studied this in more detail. In the system of BRIQUET (extracted by ) Ajugoideae and Prostantheroideae have no gynobasic style, hence, the nutlets have in these two subfamilies a lateral-ventral attachment. Besides this, some genera of Labiatae have fruits without separation of nutlets, like a drupe, a situation which is frequent in Verbenaceae. However, there is rather unanimity of opinion that genera as Ajuga, Teucrium, Rosmarinus, and Prostanthera should be retained in Labiatae.
An other allied family is Boraginaceae, but that family is sharply separated from Labiatae by the position of the radicle. As BRIQUET (1895) remarked also in this family there are two types of ovary structure, gynobasic and with a terminal style, which thus supports the idea to keep Labiatae in the traditional sense. According to BRIQUET the gynobasic structure would represent a derived stage.
Subdivision. BRIQUET l.c. based his subdivision of the family almost entirely on the structure of the gynoecium and the fruit. He distinguished 8 subfamilies. I have arranged the native genera of Malesia into the 5 subfamilies which occur in Malesia as follows:
KEY TO THE SUBFAMILIES AND GENERA OF MALESIAStyle not gynobasic. Nutlets with lateral-ventral attachment, the contact surface often more than half the height of the ovary. Seed without endosperm. AjugoideaeAcrymiaAjugaCymariaTeucriumStyle gynobasic. Nutlets basally attached, with very small surface of contact.2Nutlets drupaceous with fleshy or strongly thickened exocarp and hard crustaceous endocarp. PrasioideaeGomphostemmaNutlets with dry and often thin pericarp.3Seeds more or less transverse. Embryo with a bent radicle lying on one cotyledon. Disk tubular, elongate. ScutellarioideaeScutellariaSeeds erect. Embyo with short, straight, superior radicle. Disk lobes when distinct alternate with the lobes of the ovary.4Stamens ascending or spreading and projecting straight forwards. StachyoideaeAchyrospermumAnisomelesElsholtziaEurysolenLeucasMelissaMenthaMicrotoenaMoslaParaphlomisPogostemonSalviaSaturejaStachysStamens descending, lying upon or enclosed in the lower lip. OcimoideaeAcrocephalusBasilicumCeratanthusMesonaNosemaOcimumOrthosiphonPlatostomaPlectranthus s.l.
The key to the subfamilies can obviously not well be used as the main frame of a practical, general key to the genera.
For this we have chosen the key offered by BACKER & BAKHUIZEN VAN DEN BRINK f. in the Flora of Java, in which we have inserted the 7 genera which do not occur in Java. This key has the merit to cover also the genera which are solely represented by introduced, naturalized species, viz Hyptis, Leonotis, and Leonurus, and, furthermore, those genera of which the species occur only in cultivation, either for ornamental, medicinal, commercial, or other purposes. The latter are listed concisely at the end of this revision.

Uses

By their volatile, aromatic oils of different sorts Labiatae are in frequent use and even in cultivation, for medicinal purposes, condiments, and the perfume industry. An occasional one is yielding edible tubers, e.g. Plectranthus rotundifolius. See for further data under the species.

Phytochemo

Chemical characters of Labiatae were treated in . Supplementary chemotaxonomic comments were given in . The manifold uses of members of the family as medicinal and culinary herbs, as spices and as sources of highly esteemed essential oils are based on the accumulation of different classes of secondary metabolites. A number of chemical features and trends are rather characteristic of Labiatae; including some of the most recent findings, these may be summarized as follows.
  1. Many taxa of the family are strongly aromatic. As a rule their essential oils accumulate in distinct glandular hairs. Sometimes (e.g. spp. of Pogostemon) internal glandular hairs and oil cells are present also. Depending on the species, the essential oils contain mainly monoterpenoids, sesquiterpenoids or phenylpropane derivatives. The occurrence of two to several chemotypes with regard to essential oils within many species is a highly interesting feature. Leaves of P. cablin BTH. yield the sesquiterpenoid-rich oil of patchouly which is highly esteemed in perfumery. It also contains two acidic compounds with bactericidal activity () and the two sesquiterpenc alkaloids epiguaipyridine and patchoulipyridine ().
  2. Iridoid glycosides (i.e. glucosylated cyclopentanoid non-volatile monoterpenoids: compare the reviews of and of ) were isolated from many Labiates in recent time. They are especially common in the so-called verbenoid Labiatae and in many genera of Stachydeae and seem to replace volatile isoprenoids in a number of weakly aromatic taxa. More than 25 individual iridoid glycosides including lamiol, lamiide, phlomiol (C10), melittoside, catalpol, antirrhinoside, galiridoside, harpagide, ajugol and repto-side (all with a decarboxylated C9) are known at present from the genera Ajuga, Anisomeles, Eremostachys, Galeopsis, Hemiandra, Lagochilus, Lamium, Leonurus, Leucas, Melittis, Microcorys, Molucella, Phlomis, Physostegia, Prasium, Prostanthera, Salazaria, Scutellaria, Sideritis, Stachys s.I., Teucrium, and Trichostema. Some species of Nepeta and Teucrium marurn L. do not glucosylate the cyclopentanoid monoterpenoids, such as the nepetalactones and doli-chodial, produced by them (e.g. ). These volatile constituents of their essential oils are toxic to insects () and excite cats (Nepeta cataria!) and related mammals.
  3. Diterpenes seem to be ubiquitous in Labiates. They occur as resinous compounds, as lactonoid bitter principles, as colourless phenolic compounds and as related quinonoid pigments. Accumulation takes place either in the glandular hairs or in the tissues of leaves, stems and roots. Many of these diterpenes are biologically active; depending on structural details and the localization in the plants they may act mainly as antifeedants, antibacterial, antifungal or antinematodal constituents (e.g. ). Diterpenes were investigated very intensively in recent years; like e.g. Compositae, Labiatae proved to be very versatile with regard to diterpenoid synthesis. Monocyclic lactonoid diterpenes (ovatolide and anisomelic acid) occur in Anisomeles ovata R.BR. and A. malabarica R.BR. (). Bicylic diterpenes of the labdane-manooloxide-type seem to be very common in the family. Many representatives of this structural type were isolated from members of the genera Ballota, Lagochilus, Lasiocorys, Leonotis, Leonurus, Marrubium, Nepeta, and Sideritis. Rearranged labdane-type diterpenes with the so-called clerodane skeleton were isolated from several species of Teucrium, a few species of Salvia and Stachys and from Ajuga remota (). Phenolic and quinonoid tricyclic diterpenoids with the abietane skeleton occur in many members of the family. Examples are carnosol, royleanone, horminone, the tanshinones, fuerstione and the many coleones (e.g. ). The quinones represent the yellow to red pigments of the glandular hairs on the leaves of certain species of Coleus, Fuerstia, Horminum, Hyptis, and Plectranthus and occur also in the roots of many Labiatae. The phenolic compounds of this class occur predominantly as lactonic bitter principles in leaves (many species of Salvia, Rosmarinus officinalis L., Coleus barbatus (BTH.) AGNEW, Nepeta spp.) and accompany the quinonoid pigments in roots (compare e.g. ). Tetracyclic kaurane-type bitter diterpenes are presently known from Englerastrum scandens ALSTON and several species of Sideritis and Isodon. The latter genus also produces the enmeine-type rearranged kauranes (review: ). In the genus Sideritis pimarane-type tricyclic diterpenes, stachane-type and atisane-type tetracyclic diterpenes and trachylobane-type pentacyclic diterpenes were also detected (e.g. ). Most of the biologically active diterpenes are strongly oxigenated; epoxy, acetoxy, lactonoid and furanoid groupings occur frequently. It deserves mentioning that sometimes (e.g. the ajugarins) even a butenolide group is present; such diterpenes may be confused with cardenolides when plants are screened for cardioactive constituents. A structurally and biosynthetically different lactonoid bitter principle, ovatolide, was isolated long ago from leaves of Hyptis pectinata. A similar compound, bronolide, has been recently isolated from the Madagascan plant Tetradenia fruticosa ().
  4. Labiatae produce large amounts of triterpenes and phytosterols. Free triterpenic acids are main constituents of the cuticular waxes. In many instances ursolic and oleanolic acids predominate; they are often (e.g. Anisomeles malabarica, Hyptis emoryi, Lepechinia chamaedryoides) accompanied or replaced by betulinic acid. Recently a number of new triterpenic acids such as micromeric acid () and several oxigenated derivatives of ursolic and oleanolic acids (species of Isodon, Nepeta, Salvia, and Rosmarinus) was isolated from certain species; they are usually minor compounds of the cuticular waxes. Besides triterpenic acids, most Labiates produce appreciable amounts of triterpenic alcohols. As a rule the latter are present as acetates or related esters in resinous exudates (e.g. Salvia glutinosa) or in similar external or internal lipoid fractions. α-Amyrine, β-amyrine, lupeol, germanicol and uvaol are rather common. Recent inves tigations demonstrated the additional occurrence of betuline (Plectranthus rugosus WALL., Nepeta aragonensis LAMK) and many new compounds like anagadiol, 9,11-dehydro-α-amyrine, nivadiol, epialnusenol and 11α-hydroxy-β-amyrine in species of Nepeta and Salvia (e.g. ). Weakly hemolytic saponins seem to be wide-spread in the family; their chemistry is still scarcely known, however; most probably the sapogenins are triterpenes. According to recent Russian investigations leaves of Orthosiphon stamineus BTH. ('kumis kutjing)' contain the siphonosides A, B, C, D, and E with unidentified triterpenes as sapogenins and arabinose, glucose and galactose in the sugar chains. The ecdysone-type oxi genated sterols detected in several species of Ajuga (), but not in members of 20 other genera of Labiatae, deserve mentioning here. The phytoecdysones cyasterone, ecdysterone, ajugasterone A, B, and C were isolated from Ajuga chia, A. decumbens, A. incisa, A. iva, A. japonica, A. nipponensis, and A. turkestanica. A. decumbens contains at the same time the insect-moulting inhibitor ajugalactone (). Just as iridoid glycosides phytoecdysones seem to be restricted to the verbenoid part of Labiatae.
  5. Labiatae synthesize and accumulate large amounts of phenolic constituents; flavonoids and caffeic acid derivatives form the bulk of their phenols. Flavonoids are ubiquitous in cormophytes, but some trends of flavonoid metabolism such as replacement of flavonols by flavones, lack of proanthocyanidins and catechins, 6-hydroxylation of flavones (e.g. 6-hydroxyapigenin (= scutellarein), 6-hydroxyluteolin) and methylation of one to several of the flavonoid hydroxyls are very characteristic of Labiatae and a number of more or less closely related taxa. Many new flavonoids were isolated from the family in recent time; most of them are heavily methylated derivatives of scutellarein and 6-hydroxyluteolin; they occur either as glycosides or as glucuronides, and — the more lipophilic ones — also as free compounds in exudates, cuticular waxes and other lipoid fractions. Some medicinal plants may serve to illustrate trends in flavonoid metabolism. Eupatirin, sinensetin and three additional tetramethyl ethers of 6-hydroxyapigenin and 6-hydroxyluteolin were isolated quite recently from leaves of Orthosiphon stamineus (). Salvigenin (= 3',6,7-trimethoxy-5-hydroxyflavone) occurs free and as 5-glycoside in leaves of Salvia triloba L.f. and S. virgata JACQ. (). Roots of Scutellaria baicalensis GEORGI yielded two additional flavones, skullcap-flavone-I and -II; the latter was shown to be 2',6',6,7,8-pentamethoxy-5-hydroxyflaivone; this compound has a rather unusual B-ring substitution; leaves of the same species yielded two free flavanones, carthamidin and isocarthamidin (). Flavanones occur rarely in Labiatae; another example is didymin (= acinoside) from Monarda didyma L. and Acinos thymoides MOENCH (= Satureja acinos SCHEELE) which was shown to be the 7-rutinoside of isosakuranetin (= 5,7-dihydroxy-4'-methoxyflavanone) (). Free chrysosplenetin (formerly isolated from Chrysosplenium!) occurs in relatively large amounts in Plectranthus marrubioides HOCHST. (leaves and inflorescences: ). Flavone-C-glycosides seem to be restricted in Labiatae to those members which have the strongest affinities with Verbenaceae; they became known from members of the genera Phlomis and Teucrium. Caffeic acid is present in large amounts in practically all Labiatae. It is esterified with quinic acid (the several chlorogenic acids), glucose or with the alcoholic hydroxyl of α-hydroxydihydrocaffeic acid (the so-called rosmarinic or labiatic acid). Mixtures of these poly-phenolic constituents have some of the properties of true tannins and are described in botanical and phytomedical literature as 'tannins'. Generally they represent 1 to several percent of the dry weight of leaves and are more or less active as antibiotics, antipyretics and antioxidants. Rosmarinic acid and sugar esters of caffeic acid occur mainly in Labiatae sensu strictissimo (highly aromatic taxa with trinucleate, hexacolpate pollen grains) (compare e.g. ). Rosmarinic acid has also been isolated from leaves of Orthosiphon stamineus. A number of phenolic compounds are likely to occur rather infrequently in Labiatae. Examples are hydroquinone (herb of Majorana hortensis MOENCH: ) and lignans such as (+)-sesamin (herb of Sideritis canariensis AIT.: ), a diester of secoisolariciresinol (seed oil of Salvia plebeia R.BR.: ), and the cytotoxic constituents of leaves of Hyptis verticillata (podophyllotoxin and 4'-demethylpodophyl-lotoxin: ). The strange coumarins from Sideritis canariensis, S. montana L. (siderin = 4,7-dimethoxy-5-methylcoumarin: P. VENTURELLA C.S., Tetrahedron Letters, 1974, 279) and Leonotis nepetaefolia R.BR. (6-methoxysiderin: ) and lithospermic acid which is present in leaves of some medicinally used East Asiatic species of Lycopus belong to the same category of phenolic constituents of Labiatae.
  6. True alkaloids are unknown from Labiatae. The betaines stachydrine and betonicine are produced in large amounts by many species of Stachys and related genera like Eremostachys, Galeopsis, Lagochilus, Lamium, Leonurus, Marrubium, Panzeria, Phlomis and Sideritis. Certain medicinally used East Asiatic species of Leonurus contain leonurine and several similar guanidine derivatives (). The alkaloids described in literature for Rosmarinus officinalis have been shown to be artefacts of isolation.
  7. Like Scrophulariaceae, Plantaginaceae and some related families, Labiatae do not store starch in their subterranean parts; perennial species store large amounts of oligogalactosides of sucrose (raffinose, stachyose, verbascose and ajugose).
  8. Seeds of Labiatae store proteins, fatty oils and sucrose and planteose (an isomer of raffinose); starch is absent. Generally fatty oils are present in largest amounts. With regard to seed oils Labiatae can be devided roughly in two main groups; those producing oils with linolenic acid as main fatty acid and those producing oils with oleic and linolic acids as main fatty acids. The former group includes taxa with hexacolpate trinucleate pollen grains and the latter mainly taxa with tricolpate binucleate pollen grains. Besides these trends with regard to 'common' fatty acids, certain species produce seed oils with appreciable amounts of 'unusual' fatty acids such as laballenic acid (Leonotis nepetaefolium R.BR.), lamenallenic acid (Lamium purpureum L.), 5,9,12-octa-decatrienoic acids (Teucrium depression SMALL) and α-hydroxyoleic and α-hydroxy-linolic acids (Salvia nilotica MURR.) (some recent references: ).
  9. The nutlets of many Labiatae are rich in mucilage. The taxonomic significance of this character has been discussed by I. C. HEDGE (). Chemically the mucilages have only been studied in Ocimum basilicum L., O. canum SIMS, and O. gratissimwn L.; they contain two uronic acids (galacturonic and mannuronic), three hexoses (glucose, galactose, mannose) and two pentoses (arabinose, xylose); additionally rhamnose may be present ().


Summarizing it may be stated that Labiatae are characterized by an astonishingly broad spectrum of isoprenoid compounds (many types of monoterpenoids, sesquiterpenoids, diterpenoids and triterpenoids), caffeic acid derivatives and apigenin- and luteolin-derived flavonoids and by the replacement of starch-accumulation in perennial parts by oligosaccharides of the so-called stachyose series. At the same time they store mainly linolic or linoleic acid-rich oils in their starch-free seeds. True tannins and alkaloids are lacking. Their chemical characters place them convincingly in Lamiales sensu TAKHTAJAN and affirm close relationships of the latter with Scro-phulariales of the same author. At family level the chemical characters agree very well with the classification proposed by R. WUNDERLICH () and with the proposals of EL-GAZZAR & WATSON () who plead for combination and reclassification of Verbenaceae and Labiatae (compare: ). — R. HEGNAUER.