Introductory
Botany for Herbalists
- .pdf version
Plant
Anatomy and Physiology
This is a brief overview of some of the basic characteristics of
plant cell and tissue structure. I will also briefly discuss some
mechanisms plants use to move water and nutrients, and respond to
environmental changes.
One of the first divisions of the great Kingdom of plants is between
the vascular and the non-vascular plants. Vasculature is simply
a term for a network of vessels plants use to transport water; most
plants we work with are indeed vascular. But the first ones to begin
colonizing the dry land were just extensions of algae and water-plants,
and as such, possessed no internal vessels because they were used
to just soaking up water from their environment. These simpler plants
still exist: they are the mosses, liverworts and algae. Obviously,
they need a moist environment to live, or their cells will die due
to lack of water. They have no vasculature.
So vasculature evolved to allow plants to colonize areas that were
far from direct water sources, allowing them to transport water
up from the roots and into the leaf tissues. Water transport alone
was only part of the problem, however: when removed from a moist
environment, plants faced two other issues: how to prevent death
by loss of moisture through their green parts, and how to spread
pollen and reproduce without the aid of water.
In the first case, water loss was prevented through the development
of the cuticle, a waterproof protective coating on leaves and stems.
This functions quite well – but the plant must also be able
to breathe (both CO2 and O2), so the stomata, small holes in the
cuticle, developed. The plants can open and close these stomata
as needed, to conserve water during the heat of the day.
In the second case, seeds were developed. Most algae and mosses
secrete their sperm, unprotected, into the moist environment. Here,
it could survive quite well until fertilization. But in a dry environment,
such unprotected pollen would quickly dry out and die: therefore,
seeds and protected spores and pollen were developed, basically
by surrounding the sperm and eggs in their own, extra-tough, cuticle
and providing the plants with enzymes to break that cuticle down
when the time was right.
So, in sum, plants developed vasculature, cuticles and stomata,
and protected reproductive cells in order to cope with the dryness
of life outside the oceans, lakes and streams.
The next major division of vascular plants separated those whose
reproductive cells, once fertilized, are left out in the open from
those who encase them in an ovary and flower. The first plants are
called gymnosperms, or ‘naked-seed’; the second are
termed angiosperms, and comprise all of the flowering plants. For
our purposes (since a great majority of the herbs we use are angiosperms),
we will continue our discussion in relation to the flowering plants
only.
Here, at right, is a diagram of a basic, generalized plant cell,
the essential unit of all plants. Don’t concern yourself too
much with the internal pieces, except from noting that plant cells
possess a cell wall, which is hard and sturdy and helps give plants
their rigidity; chloroplasts where photosynthesis takes place; and
sugar and starch, foodstuff for the plant, which we will discuss
in the context of nutrient transport. The rest of the structures
are mostly concerned with reading DNA and creating proteins for
development and regulation of the plant’s life.
To get a bit more specific, there are three basic sub-divisions
of plant cells, depending on the general purpose they serve in the
plant: 1) the ‘worker’ cells, called parenchyma, that
contain an abundance of chloroplasts, sugars and starches, and both
produce and store energy for the plant; 2) the ‘structure’
cells, called collenchyma and sclerenchyma, which die as soon as
they are fully grown, but leave their solid cell walls to give structure
to the plant; 3) the ‘vascular’ cells, called vessel
elements, tracheids, and sieve-tube elements, which allow for the
transport of water and nutrients through openings in their cell
walls.
A
simple plant tissue consists of three basic layers: the first is
the epidermis, which is sheathed by the cuticle, and is the protective
barrier for the plant, as well as containing the stomata, or pores;
the second is the mesophyll or ground tissue, which can serve both
as structure and as work tissue (in the leaves, for example, it
will contain parenchyma loaded with chloroplasts); the third is
the vascular layer, which consists of xylem (for water and mineral
transport) and phloem (for sugar transport). In the diagram, you
are looking at the cross-section of a leaf; however, this basic
structure will exist at all levels of the plant, from root, to trunk
or stem, and into leaves and flowers.
The
basic parts of a plant, which determine its structure and shape,
are the roots (comprised of main root, side roots, and rootlets),
the shoot (the central stem or trunk, as well as any branching side-stems),
the petioles (small stems that the leaves and flowers are attached
to), and leaves and flowers. The places where petioles attach to
the shoot are known as nodes. The first leaves, which are not true
leaves, of a seedling are termed the cotyledons. The plant grows
from a seed, upward and downward, as well as outward (it widens)
during the course of its life. Such growth occurs at the meristems,
which are of two different types: the tips of the shoot and or the
root are termed apical meristems, and they determine the vertical
growth of the plant. The inner tissue of the shoot and roots, called
the cambium (also known as the secondary meristem), also grows,
but outward rather than upward. Growth in most plants is indeterminate,
meaning the plant can expand in a variety of different ways depending
on growing conditions and environmental factors. Witness, for example,
the difference in trees grown in the open (wide, branching) versus
those that grow in a crowded forest (slender and tall).
Plant
physiology is incredibly complex, but for our purposes we will discuss
three basic processes that occur: the movement of water and ionic
solutes, the movement of sugar and other nutrients, and the sensory
/ hormonal adaptation processes. But before we can enter into plant
physiology, we will need to quickly discuss the concept of osmosis.
Osmosis is a simple physical phenomenon that involves water and
ions or molecules (collectively called solutes) that are dissolved
in the water. Imagine you had a container with two sides that were
separated by a membrane, or barrier, that wasn’t quite waterproof
but could still effectively block dissolved substances (a semi-permeable
membrane). On the right of the container you has water with a high
concentration of solutes; on the left, water that had much fewer
solutes. Osmosis tells us that the water will attempt to equalize
the concentrations on each side: therefore, it will tend to move
from the left to the right, diluting the concentrated solution until
the two sides are equal. The law of osmosis is summed up this way:
water tends to move against the concentration gradient, from low
concentration to high concentration, until equilibrium or balance
is reached. It will even work against gravity to do this! And this
is where water transport in plants comes in.
How do plants and trees move water sometimes hundreds of feet up
their stems and trunks? We already know that they use their vascular
tissue, specifically the xylem, to do this. But how exactly does
it work? The sort answer is, by a combination of osmosis and hydrogen
bonding. Remember the stomata in the leaves? Just like pores in
humans, plants use the stomata to transpire water, allowing it to
evaporate from their leaves. When that water evaporates, it leaves
a little ‘gap’ inside the leaf where water used to be,
and it also makes the water that remains in the leaves a bit more
concentrated with solutes. The gap creates what’s known as
a meniscus, a bowl-shaped structure created by the surface tension
in the water. Surface tension is there thanks to hydrogen bonding,
the peculiar quality of water that helps it ‘stick together’
(remember this from inorganic chemistry?). As water transpires and
the meniscus gets stronger, it sets up a negative pressure (basically,
a gentle vacuum) inside the leaf. The water in the leaf’s
veins gets sucked up a little bit to fill that gap, and also to
dilute the remaining liquid which has become more concentrated due
to transpiration. And basically, if water is moving inside the leaf’s
little veins, it’s moving inside the bigger veins, and all
the way down the xylem into the roots, where it gets sucked out
of the soil to balance out the whole system. So, in essence, transpiration
sets up a pressure and osmotic gradient inside the plant that causes
water to move up the stem to replace water that’s been lost.
If there’s not enough moisture in the soil, the water will
come out of the plant’s cells, at it will wilt or dry out.
If this isn’t remedied quickly, the cells will begin to die.
There is an interesting observation related to the osmotic gradient
necessary for water absorption. If plants are to function correctly,
they need to have more solutes inside them than in the soil –
otherwise water will want to move out of the roots, not in! Well,
conventional agri-business with its industrial farming techniques
has run into this very problem: if you keep adding chemical fertilizers
that are predominantly ionic to the soil, and couple this with irrigation
using water that is rich in solutes, the soil will become saturated
and get to the point where water can no longer flow up the plant’s
stem to nourish its growth. The soil has lost all its fertility.
This is happening in farmland all across our country, and the world.
You’d think that science could teach itself a little lesson
on this one!
The transport of sugar and other nutrients occurs in the phloem,
the other type of vascular tissue in plants. Simply put, sugars
move from sources to ‘sinks’, or destinations. In the
summer, the leaves are sources, producing large amounts of sugar
from photosynthesis. The phloem moves these sugars down into the
roots, where they are stored for later use, and the remaining are
used up by the plant to grow, develop flowers and seeds, and perform
other metabolic activities. In the spring, the roots send out their
stored sugars to the apical meristems, where they are used to open
buds and turn them into leaves for the summer season. The basic
difference between sugar movement and water movement in plants is
that sugars require energy to be moved, while water just flows almost
automatically. Plants accomplish this energy expenditure through
the use of special cells, the sieve-tube elements, that have membranes
on them capable of directing sugar movement in response to energy
expenditure, like miniature pumps.
Some plants cannot produce sugars and nutrients in enough quantity
on their own. These plants need to latch on to another, more self-reliant
species, and take nutrients from it. In this case, we are obviously
dealing with plant parasites. Other times, certain species will
rely on trapping insects and decaying matter from the environment
and processing it for their nutrition; these are the carnivorous
plants.
Through a complex dance of hormones and other chemicals, plants
are able to sense and adapt to their environments. They can respond
to light, gravity, and touch quite dramatically, and also interact
symbiotically with mushrooms (to form mycorrhizae in the roots for
aid in nutrient absorption) or bacteria (famously, the nitrogen-fixing
Rhyzobium species that interact with members of the Pea family).
Blue light is mostly responsible for direct plant growth. If you
expose a plant to a light source, it will tend to bend towards the
light as its apical meristem grows less on the light side, and more
on the dark side, causing it to turn. But if you remove blue light
from the spectrum, no such bending occurs. Near-red light is responsible
for germination in those species whose seeds are light-dependent.
Infrared light, which is predominant in the shade, causes light-loving
plants to grown longer and leggier, as their apical meristems go
into overdrive.
Gravity has a direct effect on meristem tissue, causing roots to
bend towards the force and shoots to bend away. There are many theories
as to why this is; one interesting one postulates that special compounds
known as amyloplasts, which are pretty dense, sink to the bottom
of cells and, in roots, inhibit cell growth, while in shoots they
stimulate it. This causes the tissues to bend in the appropriate
direction.
Plants possess an electrical field, like any other living being.
This is a scientifically documented fact, and is used to explain
how plants can move quickly (like the sunflower following the sun),
or change their growth habits in response to touch or wind, becoming
stockier and more compact the more contact they receive. It is almost
as if the electrical field functioned as a ‘buffer’,
needing to become stronger and more compact to protect the plant
from external stimuli. This in turn affects the density of cells
and the rate of node / leaf production.
Additionally, plant cells are constantly photosynthesizing (obtaining
energy from sunlight) in a process that involves and generates electrical
fields and oscillations. The chloroplast, which is contained in
the plant cell and carries out photosynthesis using specialized
biochemical subunits called cytochromes, generates energy through
the conversion of photons (light energy) into electrons (electricity).
Reception and conversion of photons occur in a pulsing rhythm and
are highly variable – setting up oscillations in every green
plant tissue, another electric field phenomenon. Fascinating stuff
– I can hardly believe that is all this electrical field can
do! Perhaps if it can sense and oscillate (modulate), it can also
–dare I say- communicate?!?
Plant hormones are responsible for these changes in growth patterns;
they are the ones that ‘signal’ cells whether to grow
more or less, or whether to change into a leaf, flower, or root
hair. Most are derivatives of a simple alkaloid structure, with
and acid group attached. Some important ones are: auxin, which plays
a role in differentiation of tissues and in initiating the sensory
responses discussed above; gibberellic acid, which stimulates growth;
abscisic acid, which inhibits growth; kinin, which promotes cell
division; and ethylene (actually, just a simple gas) which stimulates
the ripening of fruit.
The
parts of an ‘ideal’ flower
‘Ideal’ just means ‘most common’, and serves
to indicate what basic flower anatomy is, from a general point of
view. Different plant families will have very different anatomies,
but the basic parts will always remain: the calyx, which consists
of the sepals; the carpel or pistil, consisting of stigma, style
and ovary; and the stamen, consisting of anther and filament. The
calyx grows as the basic flower bud opens; there are always sepals
(which used to be the outer ‘skin’ of the flower bud),
and there may or may not be petals (some flowers don’t have
them). The seed(s) are generated in the carpel (pistil), through
fertilization by the pollen contained in the stamen(s).
The “Key” system of plant identification
Refer to Newcomb’s Wildflower guide
It
is perhaps unfortunate, but any wildflower guide will assume you
have an actual flower in front of you to look at. From that point,
based on the shape and features of the flower and coupled with the
leaf shape and its placement on the stem, you can easily find what
plant family your specimen belongs to, and probably what the actual
genus (and even species) may be.
There are three basic questions to ask when looking at a flower:
1.
How many parts does the flower have?
This refers to the number of sepals and/or petals you will find
on the flower. In the case of compound flowers, such as members
of the Aster family, you will have to find the smallest piece to
be able to count the parts of the flower. Some answers to this question
include: irregular (like the two-lipped flowers of the mint family,
or jewelweed, or orchids for example), a number from 2 to 7 (indicative
of the number of petals, sepals, and / or divisions of the ovary).
In addition, many botanical texts will refer to the arrangement
of the flowers on the plant, whether they be whorled, or tightly
wrapped around the stem, like many of the Mint family; in an umbrel,
with multiple flowers spreading from a central point connecting
to the stem, like many of the Parsley family; in a corymb, where
multiple flowers are spreading from different points at the top
of the stem, as in Yarrow; in a raceme, or elongated, spiky cluster
coming from the top of the stem, as in Black Cohosh; or in a panicle,
which is basically a set of multiple racemes joined to the stem
at different points, like with Scullcap.
2.
How are the leaves arranged on the plant?
If you are dealing with a shrub, you have limited your choices and
made identification a lot easier. If not, look at how the leaves
are arranged along the plant’s stem. Some possible ways are:
no leaves – this one is fairly obvious, and includes some
plants like Indian pipe and Ephedra; basal leaves, meaning that
no leaves extend up the flower stem, like in Plantain; alternate
leaves, meaning that leaves on either side of the stem are separated
by a gap, like in second-year Mullein; opposite leaves, meaning
that leaves on either side of the stem are at the same spot on the
stem, like most Mints; or whorled leaves, similar to opposite but
consisting of more than just a pair, and arranged radially around
the stem, like Cleavers or Bedstraw (members of the Galium family).
3.
What do the leaves look like?
This last question usually refines your identification to a single
species. Look at each individual leaf, and examine its edges: it
may be divided, meaning that the leaves are separated into multiple
leaflets, like Valerian or Ginseng; lobed, meaning it has deep divisions
that don’t quite separate the leaf into smaller leaflets,
like the Motherwort or the Opium poppy; toothed, meaning they have
a serrated edge, like most members of the Mint family; or entire,
meaning they have smooth edges, like a Milkweed.
Some common plant families that include useful medicinal herbs,
and their general characteristics.
Fabaceae
(Leguminosae)
This is the bean and pea family. Characteristic are the flowers,
shaped like a small “boat” with sails and a keel, and
the leaves, which are usually divided, compound leaves with entire
leaflets.
This family is nourishing (to people and to soil) and often used
for food, and many of its representatives contain steroidal analogues
that can be used in strengthening immunity, adjusting endocrine
function, and benignly altering illness. Remember that they are
often very powerful due to their chemistry; in older times, much
caution and care surrounded their harvest and use.
Licorice, Red Clover, Soy, Astragalus, Scotch Broom
Apiaceae
(Umbelliferae)
This is the parsley family. The flowers are usually shaped in an
umbel (hence the old family name), though there are some exceptions.
Leaves are often deeply lobed, some even lacy. The general nature
of their essences is acrid and hot, containing slightly irritating
constituents that can be useful in stimulating tissue function and
elimination (like Angelica for reproductive and GI tissue; Parsley
for urinary tissue; Wild Carrot for uterine tissue). One exception
is the true Poison Hemlock, the only member of this family to have
alkaloidal constituents. Not surprisingly, it is calming and antispasmodic
(way too calming – i.e. lethal – if taken in excess).
Many members of this family are violently poisonous.
Lamiaceae
(Labiatae)
This is the mint family. Flowers have a distinctive two-lipped trumpet
shape, and the leaves are usually toothed and opposite on the stems,
which is square. Generally, members of this family are valued for
their aromatic volatile oils, leading to a generalized use as carminatives
and antispasmodics, particularly of the GI tract. Now, a good relaxation
in the GI tract can have profound effects overall, so their use
is not limited to digestive complaints and often finds a nervine
application.
Lemon Balm, Peppermint, Pennyroyal, Scullcap, Motherwort
Asteraceae
(Compositae)
This is the sunflower family. Its characteristic is a flower made
of many smaller inflorescences, often five-parted, clustered together
like a pincushion and surrounded by common “petals”
and a corolla of sepals. While there are some generalizations to
be made about this family (often antiseptic and lymphatic), it is
very broad and diverse.
Yarrow, Echinacea, Aster, Wormwood and the Artemisias, Dandelion,
Burdock
Rosaceae
This is the rose family. It is distinguished by a classic five-part
flower that looks like an apple or wild rose blossom. This family
is usually rich in vitamins and flavonoids, good for the circulation
and immunity. There is usually a sour taste, especially in the fruit.
Rose, Apple, Hawthorn
Liliaceae
This is the lily and iris family, who, along with the grains and
grasses make up the bulk of the common monocots. They have three
or six part flowers, are usually very regular and symmetrical, and
possess long, slender, entire leaves that are usually basal. They
often contain soothing, mucilaginous constituents although this
is not universally true! Many others, like Blue Flag or Calamus,
contain some acridity (although they are also demulcent).
Solomon’s Seal, Orris, Garlic
Malvaceae
This is the mallow family, which can be taken broadly to include
Brassicas, or on its own. In the latter case, we see variable flowers
usually with four or five parts. There is usually a characteristic
fuzziness or hairiness (“stipules”) on the plant. Constituents
include mucilages and demulcents, along with some flavonoid content.
Some members are toxic (Rhodonendrons, etc…).
Marshmallow, Laurel, Okra
Papaveraceae
This is the poppy family. There are many different flower presentations
(although all tend to be ephemeral and short-lived), and the predominant
unifying characteristic of this family is acrid latex (juice) and
high alkaloid content. These are usually powerful / poisonous plants.
Opium poppy, California poppy, Celandine, Bloodroot
Ranunculaceae
This is the buttercup family. It is the “oldest” of
the flowering plant families, or closest to the root of the taxonomic
tree. Its pistils are separate, leading to individualized, separate
ovaries. Many members of this family are quite toxic, but some have
tempered their medicines to make them slightly more amenable to
human use.
Black Cohosh, Hepatica, Stavescare, Pulsatilla
Scrophulariaceae
This is the figwort family. Its members have diverse flowers, but
often they look like flowers of the Lamiaceae except that they have
three protrusions on the lower “lip”, instead of two.
Often used for “scrophula”, or recurrent skin eruptions
(therefore, decent lymphatics), they have a broad range of function.
Mullein, Lobelia, Linaria, Foxglove
Araceae
This is the wild ginger family. The flowers are usually very strange,
and diverse – some carnivorous plants are members of this
family. Their unifying characteristic is a strong acridity and powerful
counter-irritating powers.
Wild ginger, Jack-in-the-pulpit
Araliaceae
This is the ginseng family. They all seem to have palmate, divided
leaves whole leaflets are toothed. Their flower, with the exception
of Spikenard, is usually a round, globular cluster. Almost all members
of this family contain steroidal saponins, polysaccharides and specialized
compounds that have all been valued as adaptogens, blood sugar balancers,
and strength/immunity enhancers.
Ginseng, Wild Sarsaparilla, Spikenard, Devil’s Club, Siberian
Ginseng
