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.