WHAT IS MEDICAL BOTANY?

Medical botany is an expert field of study once consigned to the past and now summoned to serve the herbal renaissance. In the early 1900s, this discipline was known as pharmaceutical botany, with books such as Textbook of Pharmaceutical Botany, written by Heber W. Youngken and published from 1914 to 1938. These texts focused primarily on the botanical aspects of medicinal plants rather than their bioactivity. Alternately, pharmacognocists published textbooks throughout the 19th century on the chemistry and bioactivity of medicinal plants. The most well known is Trease and Evans Pharmacognosy, now in its 15th edition.

Today, medical botany is often simplified to the study of materia medica, natural substances that possess medicinal properties, as reflected in the newly revised edition of Medical Botany by Lewis and Elvin-Lewis (2003). This medically erudite treatment concentrates on the systems of the body and the herbs that affect these systems. Owing to a reliance on both conventional medicine and reductionistic ethnobotanical and natural products research, misinterpretations are common. Worse, a peculiar blindness to traditional medicine is sorely evident.

Medical botany is treated according to the eye of the beholder, and this chapter is no exception. From this author’s view, medical botany is, first and foremost, a subset of biology called plant biology, or botany. Specialists within plant biology include plant scientists, taxonomists, systematicists, and botanists. The study of plants involves the evolution and taxonomic ordering of plants such as the vascular divisions of pteridophyte, gymnosperm, and angiosperm species, and the use of a plant key or flora to identify plants. This latter skill requires knowledge of plant anatomy and morphology (form and structure). Plant biology additionally covers the physiology, pathology, and metabolism of plants, encompassing photosynthesis, reproduction, growth, development, defense, nutrition, population, and the ecology of plants. One classic text on botany is Biology of Plants (2003) by Peter H. Raven.

The study of plant constituents is not well covered in plant biology. Students must therefore turn to chemistry and biochemistry texts. Plant metabolism investigates how plant compounds are synthesized and the role these compounds play in the plant itself. A beginning understanding of plant metabolism and biosynthesis is covered in Biochemistry & Molecular Biology of Plants (2000) by Buchanan, Gruissem, and Jones. A more thorough approach is found in Medicinal Natural Products (2002) by Paul M. Dewick.

Medical botany requires the study of medicine, including mammalian physiology, biochemistry, pathology, and pharmacy. Medical botany can be considered a subset of botany with a primary focus on the bioactivity of plants in humans and animals. A medical botanist would be familiar with not only a vast materia medica (the tools) of herbal medicine and medical science (conventional and traditional), but also of plant biology.

Several problems plague the study of medical botany. As mentioned, modern medical botany texts tend to be written within the scope of conventional science, ignoring the traditional herbal medicine paradigm. Medicinal plant research applied to medical botany is also couched within conventional scientific methods. This poses a dilemma because the therapeutic application of plant products greatly affects their efficacy and safety. Thus, it is important to appreciate that the history of using plants for medicine originates in the realm of indigenous wisdom or traditional medicine. According to the World Health Organization (2000), traditional medicine

These two models of knowledge—traditional (indigenous) wisdom and conventional science—often do not agree. Conventional medicine, considered “evidence based,” uses concentrated chemicals with the therapeutic strategy of suppressing symptoms by inhibiting enzymes involved in normal metabolic and pathologic processes. However, the therapeutic strategy of traditional herbal medicine is to strengthen and resolve the underlying causes of pathology through gentle modulation of normal and pathologic processes. Additionally, traditional herbal products embrace complex forms of whole plant products, sometimes concentrated, but not to the degree found in conventional pharmacology (Table 10-1).

TABLE 10-1 Examples of Conventional Drugs Derived From Plants

Although the practices of traditional medicine vary by culture, several ubiquitous themes are present. One ubiquitous theme is a belief in the wisdom of the body, the vital force, which some consider an untestable philosophy akin to string theory in physics. Nonetheless, vital force is somewhat synonymous to the traditional paradigms, prana in India, and qi in China. Additionally, traditional medicine focuses on the unique constitution and physiology of the patient, whereas the focus of conventional medicine is on pathology and treatment protocol. Energetics of the patient, pathology, and the herbs themselves are also important components common to models of traditional medicine.

As an example, the use of Ephedra sinensis in traditional Chinese medicine is very different from the reductionistic use of the alkaloid, ephedrine, by companies marketing it in weight loss products. The tool is not the same as the model. Herbal medicine is a model of healing that is regulated separately from the production and sale of herbal products (the tools). In the United States, healing modalities are regulated by each state through a medical board of practitioners. Herbal products are regulated by the federal government (US Food and Drug Administration and Federal Trade Commission) as dietary supplements under the Dietary Supplement and Health Education Act (DSHEA), passed by Congress in 1994. Botanical supplements are a new category that is currently under review.

To appropriately apply knowledge gained through the discipline of medical botany, the therapeutic model must be clearly delineated. A common mistake of new herbal medicine practitioners is to confuse the model with the tool. A conventional practitioner is not practicing traditional herbal medicine if he or she is using the herb product as a drug to inhibit an enzyme. How a tool is used affects the therapeutic outcome. Thus, the study of medical botany must reflect the model of medicine and must strive to keep such distinctions obvious. Most medical botany texts today are biased toward the conventional scientific model, which is a late player in the renaissance of herbal products. Traditional models are at the core of herbal products, and, if marginalized, the efficacy and safety of these products can drastically change. Although it may be appropriate to apply an herbal product through the use of conventional pharmacology, can it be said that herbal medicine is being practiced?

An additional problem plaguing medical botany is the preferential attention to animals and lack of interest in plants. This apparent blind spot in our society is believed to be due to the human visual process and to a zoocentric attitude among our educators. Plant blindness has been defined as

Veterinarians are in a unique position to observe fascinating similarities among three major groups of organisms if they add medical botany to their expertise. Herbal medicine requires an understanding of both traditional therapeutic models and the botany and chemistry of medicinal plants—the tools employed by these models. Medical botany encompasses this latter study, although it must compete with many other disciplines important to herbal medicine practitioners. Medical botany is deeply woven throughout ethnobotany, economic botany, entomology (study of insects), plant pathology, horticulture, microbiology, mycology (fungi), molecular cell biology, and toxicology. Most practitioners can barely keep up with their own specialty! Therefore, this chapter attempts to provide a basic overview for the veterinary herbalist, while revealing the extraordinary depth of plants and explaining their role in the health of all living creatures on our planet.

TAXONOMY

Plants are multicelled organisms placed in the Eukaryote domain, which includes Protista, Fungi, and Animalia. Plants are first divided into nonvascular and vascular groups. Nonvascular plants fall into two major categories: green algae, including diatoms and slime molds; and bryophytes, including liverworts, hornworts, and mosses. These are nonvascular because they lack xylem and phloem—water- and food-conducting tissues present in vascular plants. Vascular plants are divided into pteridophytes (horsetails and club mosses), gymnosperms (pines, junipers, Ephedra), and angiosperms (monocots and dicots). Most medicinal plants are found among the 250,000 angiosperm species, supporting the theory that plants have been developing more complex chemistry, along with their more intricate morphology (Gottlieb, 2002).

Taxonomy is a branch of biology that is concerned with naming and classifying forms of life. Plants are organized into groups such as classes, orders, families, and genera according to evolutionary ancestry. Nomenclature, or the naming of plant species, is set by the International Code of Botanical Nomenclature (ICBN). These naming “rules,” which are updated periodically and published by the International Botanical Congress, are the result of agreement between taxonomists based on research and cannot be forced upon any botanist, or herbalist, for that matter. In fact, it may take decades for these changes to become accepted.

Taxonomy allows authorities to group plants according to any rule they choose. Thus, many classifications have been suggested for flowering plants. Taxonomists, systematicists, and botanists write floras based on the interpretation of their favored taxonomic authority. This is why no one can say for sure just how many plant families exist. Some authorities maintain that there are 350 plant families; others (fondly referred to as “splitters”) have divided plant genera into 520 families (Cullen, 1997). The important thing for herbalists to remember is that they must not mix up authorities. One should stick to one authority, usually the author of the flora (list of plants) of your region.

The International Code of Botanical Nomenclature has set some basic rules. A plant name (or binomial) has two parts: a genus that is grouped into a family and a species that is grouped under that genus. For example, peppermint (Mentha piperita), spearmint (M. spicata), and field mint (M. arvensis) are grouped under the genus Mentha. Genera (plural) are placed in families, which are placed in orders, which are placed in subclasses, classes, and, finally, a division. This system gives a specific plant species the same Latin name for use all over the world. New name changes turn old names into synonyms. Latin names are always italicized as indicated. Figure 10-1 gives an example of the nomenclature scheme.

Figure 10-1 System of taxonomic nomenclature.

Each Latin bionomial is followed by a shortened acronym for the author who named that particular species. For example, Cannabis sativa L. was first named by Linnaeus. When a species name is changed, the original author is placed in parentheses, with the new author following, such as Cimicifuga racemosa (L.) Nutt. This is black cohosh, a species formerly named Actaea racemosa L. Recently, Cimicifuga racemosa (L.) Nutt. was returned to the genus Actaea L. (Compton, 1998)! It will take decades for this new name to become accepted in the literature. Herbalists may want to use this new name but many botanists will continue to employ Cimicifuga. It does not matter which name is used, as long as we all understand which plant species is being referred to. History suggests that herbalists have to be bilingual. Black cohosh can be found in old Eclectic texts as Macrotys. Burdock (Arctium lappa) was once named Lappa major, and Echinacea was once Brauneria.

The use of Latin names becomes even more important for Chinese herbs that can be referred to either in pinyin, Mandarin, Korean, or Japanese. Pharmaceutical names of plants and their medicinal parts must also be mastered, such as Taraxaci folium (dandelion leaf), Salicis cortex (willow bark), or Valeriana radix (valerian root). In short, herbalists must be proficient in the many ways of naming medicinal plants. From these examples, it is easy to see why common names are moot and even dangerous to rely on.

Many changes have recently been made to the names of plants because it was discovered that some plants are not related after all. This is because plants were originally classified by morphology. We now know that many plants with similar anatomic structure are actually not closely related. Similar-looking species sometimes achieve their design through convergent, or parallel, evolution. For example, both seals and penguins possess flippers. However, seals are mammals and penguins are birds. Both organisms developed flippers through independent means, not through common ancestral traits. Chloroplast and mitochondrial DNA provide stronger evidence than physical alikeness, which can be more subjective. Thus, many plant species have been moved to other families, causing some confusion and frustration among botanists and herbalists alike.

For example, most plant species once belonging to the Scrophulariaceae (figwort family) have now been moved to other families. New DNA evidence has revealed mistakes assumed by similar morphology. For instance, Pedicularis (lousewort) and Euphrasia (eyebright) are now placed in the Orobanchaceae, along with other parasitic genera such as Orobanche (broomrape). Similarly, Veronica, Gratiola, Digitalis, Bacopa, and Chelone have been moved to the Plantaginaceae (plantain family). Science, similar to nature, is in constant flux. Herbalists should understand that these changes are the result of important new discoveries, not an attempt to make botany more complicated.

Along with changes to the names of plant species and replacement into new families, the Latin names of some plant families have been changed. The most common family changes are as follows (new then old): pea family (Fabaceae/Leguminosae), parsley family (Apiaceae/Umbelliferae), grass family (Poaceae/Graminae), mustard family (Brassicaceae/Cruciferae), mint family (Lamiaceae/Labiatae), and aster family (Asteraceae/Compositae).

It should be no surprise that plant species with similar medicinal properties are found in the same or closely related families. Plant species in the rose family (Rosaceae) commonly possess an astringent property caused by tannins and flavonoids common to this family. Glucosinolates are common in the mustard family (Brassicaceae). Species in the mint family (Lamiaceae) are often antimicrobial owing to essential oils and tannins. The nightshade family (Solanaceae) contains tropane alkaloids in many of its species, such as belladonna (Atropa belladonna), black henbane (Hyoscyamus niger), jimsonweed (Datura stramonium), nightshade (Solanum dulcamara), and mandrake (Mandragora officinarum).

PLANT IDENTIFICATION

The identification of plant material is crucial to the safety and efficacy of an herbal product. In the present manufacturing arena, plant material is often identified microscopically (cell level) but also chemically through expensive techniques such as chromatography. Adulteration, contamination, and misidentification have plagued the medicinal plant industry in the past, but such events are rarer as quality and safety procedures are put into place.

Raw plant material arrives from growers and wildcrafters in many forms: fresh, uncut, cut, sifted, and powdered. If herbal practitioners do not make their own herbal products, they must trust manufacturers to correctly identify the plant material and process and preserve the material into a product that is consistent and effective. The skills of plant identification are valuable, yet not required of herb practitioners. However, whether the practitioner is collecting the plant or relying on a harvester, the responsibility of correct identification lies with the practitioner. Thus, plant identification skills are particularly necessary.

Wild plants are identified with a plant key or flora for the local area in which the plant is found, although floras are not available for all states. Some floras, such as Manual of Vascular Plants, by Gleason, or Vascular Plants of the Pacific Northwest, by Hitchcock and Cronquist, encompass many states. Floras give lengthy, erudite descriptions of plant species employing scholarly terminology. To identify the flora or plant key for a particular country or state, one should make inquiries to a university herbarium or native plant society in the community. An illustrated glossary is essential, such as Plant Identification Terminology, by Harris and Harris. A plant cannot be keyed out unless it is in the flowering stage because most floras are based on the parts of a flower (Figure 10-2). The main parts of a flower consist of (from outside to inside) sepals, petals, stamens, and pistil. Floral diagrams (Figure 10-3) are commonly used to show the morphology and number of flower parts.

Figure 10-2 Parts of a flower.

Figure 10-3 A floral diagram.

The diagram in Figure 10-3 illustrates a flower with three sepals in the outer whorl, three petals in the next inner whorl, six stamens (with paired anthers), and a three-parted pistil. This particular diagram thus shows a monocot species, possessing flower parts in 3’s and 6’s.

Floral formulas are commonly used. However, one must first become familiar with the meaning of the symbols in the formula. The four floral series—calyx, corolla, androecium, and gynoecium (see Glossary on p. 156)—are represented as follows:

As an example, the floral formula, K5 Cz 1+(2) + 2 A 9 + 1 G 1, denotes the following:

For each floral formula, one must be familiar with the meaning of the terms used or consult a glossary. Practice is required to become proficient.

Flowers are arranged into inflorescences such as cymes, spikes, racemes, umbels, and heads. Every part of a plant can be described, including leaves, which comprise unique shapes, margins, tips, and bases. Plant identification involves the description of dozens, if not hundreds, of terms; thus, this section can go no farther. Suffice to say that keying plants is a skill gained from practice and patience, but it is very rewarding, once mastered.

PLANT ANATOMY

In a basic biology class, one learns that animal and plant cells share a common basic structure (Figure 10-4). All cells are bounded by a plasma membrane with cytoplasm inside, along with membrane-bound organelles such as a nucleus, mitochondria, peroxisomes, ribosomes, endoplasmic reticulum, and golgi complex. These organelles perform many of the same functions, whether in animal or plant cells. For example, the principal function of mitochondria is to generate energy in the form of adenine triphosphate (ATP). The main differences, seen in Box 10-1, are that animal cells contain lysosomes, centrioles, and sometimes flagella (organelles that provide locomotion for the cell, such as in sperm cells). Plant cells, on the other hand, are unique in that they possess a cell wall, plastids, a vacuole, and plasmodesmata.

Figure 10-4 The major similarities and differences between animal (A) and plant (B) cells.

The cell wall is the most distinctive feature of plant cells that is absent in animal cells. Cell walls are rich in cellulose, pectin, hemicelluloses, glycoproteins, and lignin, a structural compound that gives plants strength and rigidity (not to be confused with lignan, a bioactive compound found in many medicinal herbs). The cell wall is external to the plasma membrane of the cell. Thus, it is a layer that is not found in animal cells.

Plastids are the next most distinctive feature of plant cells. Plastids reproduce by fission and are semiautonomous. Three types of plastids are found in plant cells: chloroplasts, responsible for photosynthesis and production of many secondary compounds; chromoplasts, responsible for pigment coloration of plant tissues; and amyloplasts (leucoplasts), responsible for the formation of starch grains in storage tissues such as roots. These plastids can morph into each other, depending on environmental and developmental conditions. Think of the green coloration on the tops of carrots when they are exposed to sunlight in the garden. Chloroplasts are able to synthesize some amino acids, as well as some fatty acids. We will see later that chloroplasts also produce monoterpenes, diterpenes, carotenes, phytol, and ubiquinone.

Vacuoles are found only in plant cells. They are surrounded by a single membrane (the tonoplast) and can take up much of the cell volume. They are filled with cell sap (mostly water) and store hydrophilic compounds such as anthocyanins, alkaloids, nonprotein amino acids, saponins, glycosides, flavonoids, tannins, cyanogens, amines, glucosinolates, and some primary compounds.

Just as in animals, plant cells have a plasma membrane that regulates the exchange of substances within the cell and also controls the passage of materials into and out of the cell. Chemical homeostasis is just as important in a plant cell as in an animal cell. However, it must be remembered that the major difference is the cell wall. Therefore, passage of materials through the cell wall requires different strategies than those used in animal cells.

Plant cells are connected together by the plasmodesmata, which provide a cytoplasmic pathway for transport between cells of substances such as viruses, RNA, and transcription factors. The plasmodesmata are similar to the gap junctions of animal cells in that they allow movement of constituents from one cell to the next.

Signal transduction and secondary messaging also occur in plant cells. External and internal stimuli activate receptor proteins and provide signals that trigger complex signal transduction processes. Many plant signaling pathways are very similar to those found in animals. GTPases, phospholipids, calcium signaling networks, and protein kinases are important components of plant signaling processes that are also found in animal systems. Despite the major differences between plant and animal cells, the laws of energy and the processes of glycolysis and the citric acid cycle are similar in plants. Although plants can synthesize unique substances, plants contain many of the same enzymes that are found in animals. This is one reason why plants can be used to produce vaccines and human proteins such as antibodies.

The vascular system of plants is made up of the xylem and the phloem. Water traverses upward in the plant through the xylem. Food manufactured in the photosynthetic parts of the plant is transported through the phloem and is stored as starch, whereas animals store food as glycogen and fat.

Similar to animals, plants synthesize hormones that have roles in growth and development, as well as in defense and immunity. Plant scientists do not know as much about plant hormones as medical scientists know about human hormones. This is unfortunately due to both emphasis in the science and funding. It is interesting to note that some plants manufacture hormones that are also found in animals, such as serotonin, melatonin, and acetylcholine. The section on similarities in communication, defense, and detoxification elaborates on this subject.

Medicinal plant products originate from various parts of a plant. Knowing where the medicinal compounds are stored in a plant and how plant material should be handled, so as to preserve those compounds, is of great value to an herbalist. Bioactive compounds are not found uniformly through a plant but may exist only in the roots or may be highest in the flower. In some cases, a different part of the plant becomes an important source of bioactive compounds, such as in the leaf of Echinacea purpurea, instead of the root. Bioactive constituents often vary with specific parts of a plant. For example, the hypocotyle is the bioactive part of maca (Lepidium meyenii), the inflorescence is the part most valued for Arnica, and the leaf is most highly prized for green tea (Camellia sinensis).

Some plant compounds do not become active until they are broken down by enzymes stored in a different area within the plant. Some defense compounds are safely stored next to a vesicle that contains the enzymes needed to transmute them to the defense form. Crushing these tissues, whether by an herbivore or by collection, drying, or processing procedures, often combines the necessary ingredients. In garlic, allinase combined with alliin forms allicin, a potent antimicrobial. Young leaves of Catharanthus roseus (Madagascar periwinkle) accumulate glucoalkaloid strictosidine in the vacuole. Surrounding this vacuole are high levels of an enzyme that, when mixed with strictosidine, turns into a strong, protective antimicrobial compound (Verpoorte, 1998).

Plants commonly store volatile oils in glandular hairs on the surfaces of leaves and flowers. Powdering leaves may cause bioactive volatiles to escape, thus reducing the potency of the plant material. Therefore, storing dried leaves in as large a form as possible and not powdering until the last possible moment may be the best strategy for assuring potency. Understanding where plant compounds are stored also suggests which plant parts and what time of the year is best to collect plants.

Plant compounds are made in specific parts of the cell and are transported and stored in specific areas of the plant cell based on their polarity (Figures 10-5 and 10-6; Box 10-2). The choice of where these compounds are stored depends greatly on the hydrophobicity and hydrophilicity of the compound. For example, hydrophilic compounds such as flavonoids and tannins tend to be stored in the vacuoles, laticifers, and apoplasts of plant tissues. Lipophilic compounds such as terpenes, waxes, and anthraquinones tend to be stored in resin ducts, oil cells, and trichomes (Figure 10-6). It may be surprising to the reader that plant scientists understand little of how plant compounds are transported to storage compartments such as trichomes, far from their source of manufacture. In fact, scientists only recently discovered what triggers flowering! Plant chemistry and natural product research trudges rather slowly behind human and mammalian biochemistry and physiology.

Figure 10-5 Trichomes on the surfaces of leaves store lipophilic compounds such as volatile oils.

Figure 10-6 Plant compartments used for storage of various compounds.

BOX 10-2 Hydrophilic and Hydrophobic Plant Compounds and Their Storage Compartments

HYDROPHILIC COMPOUNDS

HYDROPHOBIC COMPOUNDS

Vacuole • Alkaloids, nonprotein amino acids, saponins, terpenoids • Glycosides, flavonoids, tannins, anthocyanins, glucosinolates, cyanogens, amines Lacticifer • Nonprotein amino acids, alkaloids, cyanogens, cardiac glycosides Apoplast • Tannins

Cuticle • Waxes, lipophilic flavonoids Trichomes • Monoterpenes, sesquiterpenes Resin Ducts < div class='tao-gold-member'> Only gold members can continue reading. Log In or Register to continue Share this: Click to share on Twitter (Opens in new window) Click to share on Facebook (Opens in new window) Related Related posts: 13: Herbal Energetics: A Key to Efficacy in Herbal Medicine 17: Conserving Medicinal Plant Biodiversity 6: Ayurvedic Veterinary Medicine: Principles and Practices 24: Materia Medica Stay updated, free articles. Join our Telegram channel Join Tags: Veterinary Herbal Medicine Jul 18, 2016 | Posted by admin in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on 10: Medical Botany Full access? Get Clinical Tree Get Clinical Tree app for offline access Get Clinical Tree app for offline access