Families yielding important phytopharmaceuticals

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Chapter 4 Families yielding important phytopharmaceuticals

Systematics has always been an important tool in pharmacognostical practice and research. Related families often contain similar types of compounds and, therefore, may have similar beneficial or toxic effects. Consequently, an understanding of the systematic position of a medicinal plant species allows some deductions to be made about the (biologically active) secondary natural products from the species. For example, many members of the mint family are known to contain essential oil.

In this chapter, the pharmaceutically most important families are highlighted, especially those that have yielded many, or very important, botanical drugs. Since a species may yield several botanical drugs (e.g. from the flowers and the leaves), these are not included in this chapter, but can be found in Part B. Here, 20 families (out of a total of more than 200 recognized families) have been selected as being particularly important or interesting and are presented in alphabetical order within the groupings angiosperms and gymnosperms. The families are not classified further; more detailed information on the systematic position of these families can be found in relevant botanical textbooks (see further reading).

Angiosperms (magnoliphyta)

These are the plants we commonly know as ‘fruitbearing plants’ – i.e. the seed is covered by closed carpels. The fruit are sometimes very large and yield many of the economically important botanical products used because of their nutritional properties. An important characteristic of these plants is double fertilization, in which cells other than the egg unite during the fertilization to give a triploid endosperm. This then develops into the fruit, which may also include other parts of the flowers. The flowers are typically fertilized by animals (i.e. zoogamous; mostly insects, but also birds, bats and spiders). Many species of this huge group have secondarily lost this trait and are fertilized with the help of the wind (e.g. oak, birch). At least 240,000 species of angiosperms are known, making it the largest group of plants. Many estimates, however, are much higher.

The taxon was originally split into two large groups – the Dicotyledoneae and the Monocotyledoneae – distinguished, inter alia, by the different number of cotyledons (primary leaves), but modern systematic classifications reject this division into only two groups.

Alliaceae (‘monocotyledoneae’)

Allium is the only important genus of this family, which includes not only important food plants such as the common onion (Allium cepa L.), leek (A. porrum L.) and chives (A. schoenoprasum L.), but also the medicinal plant garlic (A. sativum L.). The genus is often included in the Liliaceae (i.e. the broadly defined lily family).

Chemical characteristics of the family

The genus Allium is particularly well known for very simple sulphur-containing compounds, especially alliin and allicin (Fig. 4.1), which are thought to be involved in the reported pharmacological activities of the plant as a bactericidal antibiotic, in the treatment of arterial hypertension and in the prevention of arteriosclerosis and stroke.

Fig. 4.1

Apiaceae (also called umbelliferae)

Important medicinal plants in the family (see p. 215-216, Chapter 14)

• Carum carvi L. (caraway), a carminative and also important as a spice

• Coriandrum sativum L. (coriander), a carminative and also important as a spice

• Foeniculum vulgare Miller (fennel), a mild carminative

• Levisticum officinale Koch (lovage), a carminative and antidyspeptic

• Pimpinella anisum L. (anise-fruit, wrongly called ‘seed’), an expectorant, spasmolytic and carminative.

Morphological characteristics of the family

This family of nearly exclusively herbaceous species is characterized by hermaphrodite flowers in a double umbel (Fig. 4.2); note that the closely related Araliaceae have a simple umbel. Typical for the family are the furrowed stems and hollow internodes, leaves with a sheathing base and generally a much divided lamina. The flowers are relatively inconspicuous, with two pistils, an inferior gynaecium with two carpels, a small calyx and generally a white to greenish corolla, with free petals and sepals.

Fig. 4.2 Double umbel.

Distribution

Members of this family, which has about 3000 species, are mostly native to temperate regions of the northern hemisphere.

Chemical characteristics of the family

Unlike the Araliaceae, members of this family are often rich in essential oil, which is one of the main reasons for the pharmaceutical importance of many of the apiaceous drugs (see above). Also common are 17-carbon skeleton polyacetylenes, which are sometimes poisonous, and (furano-)coumarins, which are responsible for phototoxic effects (e.g. in Heracleum mantegazzianum Sommier and Levier, hogweed). Some species accumulate alkaloids (e.g. the toxic coniine from hemlock, Conium maculatum L.).

Araliaceae

Important medicinal plants from the family

• Hedera helix L. [(common) ivy], used as a cough remedy

• Panax ginseng C. A. Meyer (ginseng), used as an adaptogene (a very ill-defined category) and to combat mental and physical stress [and sometimes replaced by Eleutherococcus (Acanthopanax) senticosus (Rupr. and Maxim) Maxim from the same family].

Morphological characteristics of the family

This family consists mostly of woody species, characterized by hermaphrodite flowers in a simple umbel (see the closely related Apiaceae with a double umbel). The leaf lobes are hand-shaped, and the flowers relatively inconspicuous with two pistils, an inferior gynaecium, a small calyx and generally a white to greenish corolla, with free petals and sepals.

Distribution

This family of > 700 species is widely dispersed in tropical and subtropical Asia and in the Americas. Hedera helix is the only species native to Europe.

Chemical characteristics of the family

Of particular importance from a pharmacognostical perspective are the saponins, triterpenoids and some acetylenic compounds. The triterpenoids (ginsengosides) are implicated in the pharmacological effects of Panax ginseng, while saponins (hederasaponins) are of relevance for the secretolytic effect of Hedera helix.

Asphodelaceae (‘monocotyledoneae’)

This family is often included in the Liliaceae (lily family).

Important medicinal plants from the family

• Aloe vera (L.) Burman f. (syn. Aloe barbadensis, Barbardos aloe) and A. ferox Miller (Cape aloe), both strong purgatives (see p206 and 208). Aloe leaves contain a gel which is also applied topically for skin conditions; for botanical description. (see p. 286, Chapter 22).

Morphological characteristics of the family

Members of this family are generally perennials, and, in the case of Aloe, usually woody, with a basal rosette and the typical radial hermaphrodite flower structure of the Liliales. The petals and sepals are identical in form and colour, and composed of 3+3 free or fused, 3+3 free stamens and three fused superior carpels.

Distribution

This family, with about 600 species, is widely distributed in South Africa (a characteristic element of the Cape flora); some species occur naturally in the Mediterranean (Asphodelus).

Chemical characteristics of the family

Typical for the genus Aloe are anthranoids and anthraglycosides (aloe-emodin), which are responsible for the species’ laxative effects, as well as polysaccharides accumulating in the leaves. Contrary to other related families, the Asphodelaceae do not accumulate steroidal saponins.

Asteraceae – the ‘daisy’ family (also known as compositae)

This large family has kept botanists busy for many centuries and still no universally accepted classification exists. All members of the family have a complex inflorescence (the capitula), which gave rise to the older name of the family: Compositae (= inflorescence composed of many flowers). In other features, the family is rather diverse, especially with respect to its chemistry.

Important medicinal plants from the family

• Arnica montana L. (arnica), used topically, especially for bruises

• Artemisia absinthum L. (wormwood or absinthium), used as a bitter tonic and choleretic

• Calendula officinalis L. (marigold), used topically, especially for some skin afflictions

• Cnicus benedictus L. (cnicus), used as a cholagogue (a bitter aromatic stimulant)

• Cynara scolymus L. (artichoke), used in the treatment of liver and gallbladder complaints and several other conditions

• Echinacea angustifolia DC., E. pallida Nuttall and E. purpurea (L.) Moench (Cone flower), now commonly used as an immunostimulant

• Matricaria recutita L. (chamomille/camomille; several botanical synonyms are also commonly used, including Chamomilla recutita and Matricaria chamomilla) (see Chapter 14, p. 208).

• Tussilago farfara L. (coltsfoot), a now little used expectorant and demulcent.

Morphological characteristics of the family (Fig. 4.3)

The family is largely composed of herbaceous and shrubby species, but some very conspicuous trees are also known. The most important morphological trait is the complex flower head, a flower-like structure, which may in fact be composed of a few or many flowers (capitulum or pseudanthium). In some sections of the family (e.g. the subfamily Lactucoideae, which includes lettuce and dandelion), only ligulate (tongue- shaped) or disk (ray) florets are present in the dense heads. In the other major segment (subfamily Asteroideae), both ligulate and radiate/discoid flowers are present on the same flower head, the former generally forming an outer, showy ring with the inner often containing large amounts of pollen. The flowers are epigynous, bisexual or sometimes female, sterile or functionally male. The (outer) calyx has five fused sepals and in many instances later develops into a pappus (featherlike in dandelions, in other instances more bristly), which is used as a means for dispersing the fruit; it is lacking in many other taxa. The fused petals (generally five) form a tubus or a ligula. The two gynaecia are epigynous and develop into tiny, nut-like fruits (achene or cypsela). The leaves are generally spirally arranged, simple, dissect or more or less compound.

Distribution

More than 21,000 species are known from practically all parts of the world, with the exception of Antarctica, and the family has found niches in a large variety of ecosystems. The family is particularly well-represented in Central America and southern North America (Mexico).

Chemical characteristics of the family

A typical chemical trait of this family is the presence of polyfructanes (especially inulin) as storage carbohydrates (instead of polysaccharides) in perennial taxa. Inulin-containing drugs are used for preparing malted coffee (e.g. from the rootstocks of Cichorium intybus, chicory). In many taxa, some segments of the family accumulate sesquiterpene lactones (typically with 15-carbon atoms such as parthenolide; Fig. 4.4), which are important natural products responsible for the pharmacological effects of many botanical drugs such as Chrysanthemum parthenium (feverfew) and Arnica montana (arnica). Polyacetylenic compounds (polyenes), and essential oil, are also widely distributed. Some taxa accumulate pyrrolizidine alkaloids, which, for example, are present in Tussilago farfara (coltsfoot) in very small amounts. Many of these alkaloids are known for their hepatotoxic effects. Other taxa accumulate unusual diterpenoids; the diterpene glycoside stevioside (Fig. 4.4), for example, is of interest because of its intensely sweet taste.

Fig. 4.3 (a) Two members of the genus Matricaria. (Left) Matricaria chamomilla L. is aromatic and used medicinally. (Right) Matricaria maritima L. subsp. inodora Schultz [= Tripleurospermum perforatum (Mérat) Wagenitz], also known as Matricaria inodora, is not aromatic and is not used medicinally. The illustration shows typical morphological differences in these two species, such as the form of the flower heads and the fruit, but it also shows how similar the two species are in many other characteristics. From Fitch (1924). (b) Schematic of typical flower heads (a capitulum) of the Asteraceae (compositae). df, disk flowers; tf, tubular flowers; in, involucre, from Brimble (1942).

Fig. 4.4

Caesalpiniaceae

This family was formerly part of the Leguminosae (or Fabaceae) and is closely related to two other families: the Fabaceae (see below) and the Mimosaceae (not discussed). Many contain nitrogen-fixing bacteria in root nodules. This symbiotic relationship is beneficial to both partners (for the plant, increased availability of physiologically usable nitrogen; for the bacterium, protection and optimal conditions for growth).

Important medicinal plants from the family

• Cassia senna L. and C. angustifolia Vahl (Senna), used as a cathartic.

Morphological characteristics of the family (Fig. 4.5)

Nearly all of the taxa are shrubs and trees. Typically the leaves are pinnate. The free or fused calyx is composed of five sepals, the corolla of five generally free petals, the androecium of ten stamens, with many taxa showing a reduction in the number of stamens (five) or the development of staminodes instead of stamens. The flowers are zygomorphic and have a very characteristic shape, if seen from above, resembling a shallow cup.

Distribution

The 2000 species of this family are mostly native to tropical and subtropical regions, with some species common in the Mediterranean region. The family includes the ornamental Cercis siliquastrum L. (the Judas tree), native to the western Mediterranean, which according to (very doubtful) legend was the tree on which Judas Iscariot hanged himself.

Chemical characteristics of the family

From a pharmaceutical perspective the presence of anthranoides with strong laxative effects is of particular interest. Other taxa accumulate alkaloids, such as the diterpene alkaloids of the toxic Erythrophleum.

Fabaceae

This family is also classified together with the Mimosaceae and the Caesalpiniaceae as the Leguminosae (or Fabaceae, s.l.; see note under Caesalpiniaceae). One of its most well-known characteristics is that many of its taxa are able to bind atmospheric nitrogen.

Important medicinal plants from the family

• Cytisus scoparius (L.) Link (common or Scotch broom), which yields sparteine (formerly used in cardiac arrhythmias, as an oxytoxic, and in hypotonia to raise blood pressure)

• Glycyrrhiza glabra L. (liquorice), used as an expectorant and for many other purposes

• Melilotus officinalis L. (melilot or sweet clover); the anticoagulant drug warfarin was developed from dicoumarol, first isolated from spoiled hay of sweet clover

• Physostigma venenosum Balfour (Calabar bean), a traditional West African arrow poison, which contains the cholinesterase inhibitor physostigmine, used as a myotic in glaucoma, in postoperative paralysis of the intestine and to counteract atropine poisoning.

Morphological characteristics of the family

This family is characterized by a large number of derived traits. Most of the taxa of this family are herbaceous, sometimes shrubby and only very rarely trees. Typically, the leaves are pinnate and sometimes the terminal one is modified to form a tendril, used for climbing. Bipinnate leaves are not found in this family. The five sepals are at least basally united. The corolla is formed of five petals and has a very characteristic butterfly-like shape (papilionaceous), with the two lower petals fused and forming a keel-shaped structure, the two lateral ones protruding on both sides of the flower and the largest petal protruding above the flower, being particularly showy. The androecium of ten stamens generally forms a characteristic tubular structure with at least nine out of ten of the stamens forming a sheath. Normally, the fruit are pods, containing beans (technically called legumes) with two sutures, which open during the drying of the fruit (Fig. 4.6).

Fig. 4.5 Cassia angustifolia, a typical Caesalpiniaceae: (a) typical zygomorphic flower (yellow in its natural state); (b) fruit (one of the botanical drugs obtained from the species); (c) flowering branch showing the leaves composed of leaflets, and the inflorescence.

Modified after Frohne & Jensen (1998).

Fig. 4.6 Flower of Pisum sativum (common pea, Fabaceae, sensu stricto): (a) entire flower showing the various elements of the corolla (co; b, banner; w, wing (two); k, keel; ca calyx); (b) calyx; (c) stamens (nine fused and one free); (d) gynaecium; (e) the four petals of the corolla.

Modified after Frohne & Jensen (1998).

Distribution

This is a cosmopolitan family with about 11,000 species, and is one of the most important families. It includes many plants used as food: for example, numerous species of beans (Phaseolus and Vigna spp., Vicia faba L.), peas (Pisum sativum L.), soy [Glycine max (L.) Merrill], fodder plants (Lupinus spp.) and medicines (see above).

Chemical characteristics of the family

This large family is characterized by an impressive phytochemical diversity. Polyphenols (especially flavonoids and tannins) are common, but from a pharmaceutical perspective various types of alkaloids are probably the most interesting and pharmaceutically relevant groups of compounds. In the genera Genista and Cytisus (both commonly called broom) as well as Laburnum, quinolizidine alkaloids, including cytisine and sparteine (Fig. 4.7), are common. The hepatotoxic pyrrolizidine alkaloids are found in this family (e.g. in members of the genus Crotolaria).

Fig. 4.7

Other important groups of natural products are the isoflavonoids, known for their oestrogenic activity, and the coumarins used as anticoagulants (see Melilotus officinalis above). Glycyrrhiza glabra L. (licorice) is used because of its high content of the triterpenoid glycyrrhic acid, which, if joined to a sugar, is called glycyrrhizin (a saponin) and is used in confectionery as well as in the treatment of gastric ulcers (controversial). Last but not least, the lectins must be mentioned. These large (MW 40,000–150,000), sugar-binding proteins agglutinate red blood cells and they are a common element of the seeds of many species. Some are toxic to mammals, for example phasin from the common bean (Phaseolus spp.), which is the cause of the toxicity of uncooked beans.

Hypericaceae

This small family was formerly part of the Guttiferae and is of pharmaceutical importance because of St John’s wort, which in the last decade of the 20th century became one of the most important medicinal plants in Western medicine.

Important medicinal plants from the family

• Hypericum perforatum L. (St John’s wort) has clinically well-established effects in mild forms of depression. It has also been employed topically for inflammatory conditions of the skin.

Morphological characteristics of the family

The leaves are opposite, often dotted with glands. A characteristic feature of this family is a secondary increase in the number of stamens (polyandrous flowers). The fruit are usually capsules, but berries may occur in some species.

Distribution

This family, with about 900 species, has its main area of distribution in the tropics and in temperate regions.

Chemical characteristics of the family

The former name Guttiferae is an important indicator of a characteristic chemical feature: the presence of resins, balsam and other glands containing excretory products. For example, the hypericin glands, with a characteristic red colour, are present especially in the flowers and contain naphthodianthrones, including hypericin (Fig. 4.8) and pseudohypericin, which are characteristic for some sections of the genus. Typical for the family in general are also xanthones (found nearly exclusively in this family and in the Gentianaceae). The genus is known to accumulate flavonoids and their glycosides (rutoside, hyperoside), as well as hyperforin (Fig. 4.8) and its derivatives, which are derived from the terpenoid pathway.

Fig. 4.8

Lamiaceae

The Lamiaceae is a family yielding a high number of medicinal taxa, especially due to their high content of essential oil.

Important medicinal plants from the family

• Lavandula angustifolia Miller (lavender), a mild carminative and spasmolytic

• Melissa officinalis L. (balm), a mild sedative, carminative and spasmolytic

• Mentha arvensis L. var. piperascens Malinvand (Japanese mint), yields a commonly used essential oil (e.g. for respiratory problems)

• Mentha × piperita L. (peppermint), a commonly used carminative and spasmolytic and a hybrid between M. spicata L. and M. aquatica L. (see Chapter 14, p. 214-215)

• Mentha spicata L. (spearmint), commonly used in toothpaste and chewing gum, with mild carminative effects

• Rosmarinus officinalis L. (rosemary), a carminative and spasmolytic

• Salvia officinalis L. (sage), used as a topical antiseptic (gargling) and orally as a carminative and spasmolytic

• Thymus vulgaris L. (thyme), a carminative and spasmolytic.

Morphological characteristics of the family (Fig. 4.9)

Most of the taxa in this family are herbs or small shrubs with the young stems often being four-angled. All have opposite simple or rarely pinnate leaves. The zygomorphic flowers, with very characteristic short-stalked epidermal glands, are very typical. They are bisexual, with five fused sepals, five generally zygomorphic petals, four or two stamens and two very characteristic fused gynaecia each divided into two partial units developing into a nut with a secondary division into nutlets.

Distribution

This important family with 5600 species is cosmopolitan and has a centre of distribution spanning from the Mediterranean to Central Asia.

Chemical characteristics of the family

Essential oil in the epidermal glands is very common. Some segments of the family are known to accumulate monoterpenoid glycosides (iridoids). Many species also accumulate rosmarinic acid and other derivatives of caffeic acid. Rosmarinic acid (Fig. 4.10) is of some pharmaceutical importance because of its non-specific complement activation and inhibition of the biosynthesis of leukotrienes (leading to an anti-inflammatory effect), as well as its antiviral activity.

Fig. 4.9 Salvia officinalis (sage, Lamiaceae): (a) flowering branch showing typical leaves and the inflorescence; (b) corolla; (c) calyx.

After Frohne & Jensen (1998).

Fig. 4.10

Palmaceae (Arecaceae, Palmae, ‘Monocotyledoneae’)

The palms are particularly important because they include many species widely used as food, but in recent years at least one has become medically important.

Important medicinal plants from the family

• Serenoa repens (Bartram) Small (saw palmetto, sabal), for difficulty in micturition in benign prostate hyperplasia in the early stages.

Morphological characteristics of the family

These are generally unbranched, mostly erect, trees with primary thickening of the stem and a crown of large, often branched, leaves. The flowers are generally unisexual and radial, consisting of two whorls with three perianth leaves and six stamens. The three-lobed carpels may be free or united and develop into a berry, drupe or nut.

Distribution

The family, with about 2700 exclusively evergreen woody species, is widely distributed in the tropics and subtropics.

Chemical characteristics of the family

The accumulation of polyphenols, some relatively simple alkaloids (especially pyridine derivatives) and steroidal saponins, as well as fatty acids [coconut (Cocos nucifera L.) and oil palm (Elaeis guineensis Jacq.)] is typical. The pharmaceutical use of Serenoa repens, on the other hand, seems to be due to the presence of relatively large amounts of the ubiquitous triterpenoid β-sitosterol.

Papaveraceae

This rather small family has yielded a multitude of pharmaceutically or toxicologically important genera (e.g. Chelidonium, Eschholzia, Glaucium, Papaver) and natural products from two of its representatives are particularly widely used.

Important medicinal plants from the family

• Chelidonium majus L. (greater celandine), which yields the alkaloid chelidonine, sometimes employed as a cholagogue

• Papaver somniferum L. [(opium) poppy], which yields a multitude of pharmacologically active alkaloids and is a well-known and dangerous narcotic.

Morphological characteristics of the family (Fig. 4.11)

This family of (generally) herbs or sub-shrubs typically has spirally arranged leaves which are entire or lobed or dissected. The generally large flowers are bisexual, have an inferior gynaecium, a reduced number of sepals (two to occasionally four), often four petals and numerous stamens. The fruit is a capsule (e.g. Papaver somniferum, which is lanced to obtain opium), with valves or pores for seed dispersal.

Distribution

This small family with about 200 species is mostly confined to the northern temperate regions of the world.

Chemical characteristics of the family

The laticifers (or latex vessels) are rich in isoquinoline alkaloids, including morphine (Fig. 4.12), papaverine, codeine, thebaine and noscapine. Some of these alkaloids are typical benzylisoquinoline alkaloids (papaverine, noscapine); others are chemically modified and have two additional ring systems (morphinane-type skeleton).

Fig. 4.11 Papaver somniferum (Papaveraceae). Botanical line drawings showing: (a) a flowering shoot; (b) the fruit (a capsule), with the latex shown at the lanced parts; (c) a cross-section of the fruit.

After Frohne & Jensen (1998).

Fig. 4.12

Piperaceae

Important medicinal plants from the family

• Piper methysticum Forster f. (kava-kava), traditionally used as a mild stimulant in Oceania and now used for conditions of nervous anxiety; recent reports of liver toxicity has resulted in withdrawal in many countries

• Piper nigrum L. (black and white pepper), occasionally used in rubefacient preparations and as a spice.

Morphological characteristics of the family (Fig. 4.13)

This family of shrubs and herbs or small trees generally has simple, spirally arranged, leaves. The flowers are drastically reduced and sit in dense fleshy spikes.

Distribution

The family, with about 2000 species, is restricted to the tropics. The most important genera are Piper (including black pepper and kava-kava) and Peperomia. Some species are epiphytic (grow on other plants).

Chemical characteristics of the family

Pungent acidic amides, such as piperine, are known from several members of this family, and sometimes essential oil is present. The α-pyrone derivatives (e.g. kavain) from Piper methysticum are another group of commonly found compounds known from species of Piper.

Poaceae (‘Monocotyledoneae’)

The ‘grass’ family is not very important with respect to their bioactive contents, but many pharmaceuticals contain starches derived from corn, rice or wheat as excipients.

Important medicinal plants from the family

• Zea mays L. (maize, corn) and other cereals, a common staple food; starches are also used in antidiarrhoeal preparations.

Morphological characteristics of the family

Most are herbs, often with rhizomes, and sometimes perennial. The leaves are distichous (with a single leaf at each node and the leaves of two neighbouring nodes disposed in opposite position), elongate with parallel main veins and often with a characteristic sheath at the base. A typical feature of the family is the wind-pollinated flowers, which form spike-like inflorescences (panicles).

Distribution

This cosmopolitan family has about 9000 species. Many of the economically important food staples are from this family and are grown all over the world.

Chemical characteristics of the family

Members of this family often accumulate silicates and some members have fruits rich in polysaccharides (starch) and proteinaceous tissue, mostly in the endosperm.

Rhamnaceae

Important medicinal plants from the family

• Rhamnus purshiana DC. (American cascara) and Rhamnus frangula L. (syn. Frangula alnus, European alder, buckthorn), both used as strong purgatives.

Morphological characteristics of the family

This family mostly consists of trees with simple leaves, which are arranged spirally or opposite. The flowers are small and unisexual with an epigynous gynaecium and four or five small petals. The fruit is a drupe (fleshy exo- and mesocarp with a hard endocarp).

Distribution

A relatively small cosmopolitan, mainly tropical and subtropical, family, with about 900 species.

Chemical characteristics of the family

The family is best known pharmaceutically because some taxa accumulate anthraquinones. Also alkaloids of the benzylisoquinoline type and the cyclo-peptide type are known from many taxa.

Rubiaceae

The family yields one of the most important stimulants, coffee (Coffea arabica L. and C. canephora Pierre ex Froehner) and one of the first and most important medicinal plants brought over from the ‘New World’, cinchona bark (see below).

Important medicinal plants from the family

• Cinchona succirubra Weddell, C. calisaya Weddell and Cinchona spp. (cinchona, Peruvian bark), used as a bitter tonic, febrifuge and against malaria.

Morphological characteristics of the family

This family consists mostly of trees or shrubs, with some lianas (climbing plants) and herbs. It has simple, entire and generally decussate leaves, which are nearly always opposed and which usually have connate stipules (sometimes as large as the leaves themselves, e.g. Gallium). The usually bisexual and epigynous, insect-pollinated flowers have four to five petals and four to five sepals, and five (or four) stamens and two gynaecia. The type of fruit varies (berry, drupe capsule).

Distribution

This is a large cosmopolitan family with more than 10,000 species, particularly prominent in the tropical and warmer regions of the world.

Chemical characteristics of the family

The family is known for a large diversity of classes of natural products, including iridoids (a group of monoterpenoids), alkaloids (including indole alkaloids such as quinine from Cinchona spp.), methylxanthines such as caffeine, theobromine and theophylline, and anthranoids in some taxa (e.g. the now obsolete medicinal plant Rubia tinctorum, which was withdrawn because of its genotoxic effect).

Rutaceae

The family includes some of the most important fruitbearing plants known: the genus Citrus with orange, lemon, lime, mandarin, grapefruit, etc.

Important medicinal plants from the family

• Pilocarpus jaborandi Holmes and Pilocarpus spp. (pilocarpus), for the isolation of pilocarpine, which is used in ophthalmology

• Ruta graveolens L. (rue), formerly widely used as an emmenagogue and spasmolytic, shows strong phototoxic side effects

• Many species (especially of the genus Citrus) are aromatic and used as foods as well as in pharmacy and perfumery.

Morphological characteristics of the family

Most members of this family are trees or shrubs with spirally arranged, three pinnate or foliate (rarely simple) leaves. The bisexual flowers generally have five sepals and petals, 5+5 stamens and four or five hypogynous gynaecia.

Distribution

There are approximately 1700 species of this family distributed all over the world, but the tropics are particularly rich in them.

Chemical characteristics of the family

Essential oil is common in many taxa (Citrus, Ruta) and can be found in lysigenous secretory cavities in the parenchyma and pericarp. Alkaloids are also frequently found, especially benzyltetrahydroisoquinoline, acridone and imidazole types (pilocarpine; Fig. 4.14). The acridone alkaloids have so far only been reported from the Rutaceae. Other groups of natural products typically encountered are furano- and pyranocoumarins (e.g. bergapten from Citrus aurantium subsp. bergamia, used to flavour Earl Grey tea), as well as simple coumarins.

Fig. 4.13 Piper nigram (black pepper, Piperaceae). Line drawing of a fruiting shoot showing the typical leaves and the fruiting inflorescence.

After Frohne & Jensen (1998).

Fig. 4.14

Solanaceae

This family includes one of the most important staples Solanum tuberosum (potato) and many medicinal and toxic plants known for their highly active natural products.

Important medicinal plants from the family

• Atropa belladonna L. (deadly nightshade, atropa), Datura stramonium L. (stramonium) and Hyoscyamus niger L. (henbane), which yield alkaloids with spasmolytic and anticholinergic properties; atropine is used in ophthalmology.

Morphological characteristics of the family (Fig. 4.15)

The usually simple, lobed or pinnate/three-foliate leaves of these shrubs, herbs or trees are generally arranged spirally. The taxa have bisexual, radial flowers with five fused sepals, mostly five fused petals, five stamens and two gynaecia, which generally develop into a berry or a capsule.

Distribution

This family of about 2600 species is particularly well represented in South and Central America, but is widely distributed in most parts of the world.

Chemical characteristics of the family

Typical for the family are alkaloids, especially of the tropane, nicotine and steroidal type (Fig. 4.16). Many taxa are characterized by oxalic acid, which often forms typical structures (e.g. sand-like in Atropa belladonna, irregular crystals in Datura stramonium).

Fig. 4.15 (a) Datura stramonium (datura, Solanaceae), showing capsule enclosing the highly toxic seeds. (b) Atropa belladonna (deadly nightshade, atropa, Solanaceae), showing a flowering and fruiting branch with the violet-brown (outside) and dirty yellow (inside) flowers and the shiny black berries (highly toxic).

After Frohne & Jensen (1998).

Fig. 4.16

Zingiberaceae (‘monocotyledoneae’)

In terms of pharmaceutical usage, this family is the most important of the former class Monocotyledoneae, which includes the Liliaceae, Palmaceae and Poaceae. Many members of this family are native to the Indo-Malayan region and are thus particularly important in Asian medical systems.

Important medicinal plants from the family

• Curcuma zanthorrhiza Roxburgh (Temu lawak, Javanese turmeric)

• Curcuma longa L. (syn. C. domestica, turmeric), a commonly used spice and popular remedy used, for example, for inflammatory and liver diseases, and in most Asian medical systems for a large variety of illnesses

• Elettaria cardamomum (L.) Maton (cardamom), which is mostly used as a spice but also as a medicine

• Zingiber officinale Roscoe (ginger), used for a large variety of illnesses, including travel sickness, respiratory and gastrointestinal disorders.

Morphological characteristics of the family

Generally, the species of this family are aromatic herbs with very prominent thickened rhizomes. The latter are often rich in essential oil, stored in typical secretory cells. The leaves are arranged spirally or are distichous with a sheath around the stem (similar to the grasses). However, these sheaths are arranged in such a way that they form a stem-like structure, which supports the real, rather weak, stem. The zygomorphic and bisexual flowers are often very large and prominent and are pollinated by large, often nocturnal, insects, birds or bats.

Distribution

The family is distributed throughout the tropics, but many species are native to Asia (Indo-Malayan region).

Chemical characteristics of the family

This family is one of the few families of the former Monocotyledons which is rich in essential oil with terpenes such as borneol, camphor and cineole (all oxygen-containing monoterpenes), camphene, pinene (monoterpenes) and zingiberene (a sesquiterpene), as well as phenylpropanoids (cinnamic acid derivatives) (Fig. 4.17). Typically, these compounds accumulate in oil cells, an important microscopical characteristic of the rhizomes of the Zingiberaceae.

Fig. 4.17

Gymnosperms

This much smaller group of seed-bearing plants differs from the angiosperms in not having the seeds enclosed in carpels (the seeds are naked) and in not having double fertilization. The gymnosperms are generally fertilized with the help of the wind and are often characterized as having needles instead of broad leaves (the most important exception being Ginkgo biloba, the Chinese maidenhair tree). Only about 750 species are known, but some species are extremely important in the production of timber [European fir (Abies spp.), spruce (Picea spp.), Douglas fir (Pseudotsuga menziesii (Mirbel) Franco), all Pinaceae] and some yield medically important essential oil. The most important medicinal plant is Ginkgo biloba.

Ginkgoaceae

This is one of the most ancient families of the seed-bearing plants and had been widely distributed during the Mesozoic (180 million years ago). Only one species survives today.

Important medicinal plants from the family

• Ginkgo biloba L. (Chinese maidenhair tree), used for its memory-improving properties.

Morphological characteristics of the family (Fig. 4.18)

The characteristic fan-shaped leaves, which often have an indention at the apex, are well known. The tree does not bear fruit but has a pseudo-fruit, with the outer part of the seed (testa) developing into a fleshy cover, which has a strong unpleasant smell of butyric acid and a hard inner part. Fertilization is not by pollen but by means of microspermatozoids, a characteristic of less well-advanced plants. Another typical aspect is the separation of the deposition of the microspermatozoids on the gametophytes and fertilization (the unification of macro- and microspermatozoid). Thus the seeds found on the ground during the autumn are not yet fertilized, but will be during the winter.

Distribution

Ginkgo biloba is native to a small region in south-eastern Asia and is now widely planted in many temperate regions of the world.

Chemical characteristics of the family

The most important and a unique group of natural products are the ginkgolides (Fig. 4.19), which are unusual two-ringed diterpenoids with three lactone functions. Biflavonoids and glycosylated flavonoids are other groups of typical natural products.