BSCI 124 Lecture Notes
Undergraduate Program in Plant Biology, University of Maryland
LECTURE 26 - LEGUMES AND STARCHY STAPLES
is synonymous with pod, the fruit; the
seeds are inside
the pod or legume. Examples: peas, beans, soybeans, clover, alfalfa, peanuts.
A. Importance of legumes
Major plant sources of protein, oil.
nitrogen fixers (with
symbiotic bacteria in roots), adds N from air to plants.
The Nitrogen Cycle:
Nitrogen fixation- conversion of atmospheric nitrogen (N2) to
ammonia (NH3), which reacts with water to form ammonium
(NH4+) . N2 has strong bonds (N=N)
Performed biologically by nitrogen-fixing bacteria and cyanobacteria.
Nitrogen-fixing bacteria may by free-living in the soil, or may live
symbiotically with plants. Legumes are the only important agricultural
families that have synbiotic N-fixing bacteria.
Some nitrogen is also fixed during thunder storms, volcanic explosions, etc
Industrial (fertilizers) - takes a lot of heat and pressure
Nitrification- conversion of ammonium to nitrate (NO3-)
Performed by several species of nitrifying bacteria that live in the soil:
NH4+ --> NO3- (nitrate)
Assimilation- the intake of either ammonium or nitrate by plants and its
conversion to protein and other N-containing compounds
When animals eat plants and convert plant proteins to animal proteins, they
are also assimilating
Ammonification- the conversion of organic nitrogen (in animal wastes and
in dead organic matter) to ammonium (NH4+)
Performed by ammonifying bacteria in the soil
Denitrification- the conversion of nitrate to nitrogen gas
Performed by denitrifying bacteria in the soil: NO3- -->
B. Vegetative characteristics: Legume plants are mostly herbs, usually compound
leaves, mostly annuals but some perennials.
C. Flower, fruit, and seed characteristics:
are irregular, bilaterally symmetrical, usually 10 stamens, one pistil of
two carpels. Pollination is by bees; stamens may be cocked during growth,
triggered by bee, hits bee with pollen.
Fruit is a pod or legume, a long fruit with two rows of seeds, easily splits
on two seams, two rows of seeds; example, peas in a pod.
Seeds are large, have two large cotyledons (seed leaves) that make up most
of the seed, filled with stored food. No endosperm at maturity.
D. Nitrogen fixation was discovered in legumes, due to symbiotic association
Rhizobium species of bacteria that inhabit nodules on roots. Bacteria
take N2 from air, make it into ammonia for their
use, also secreted to plant; plant supplies carbohydrate to bacteria for
energy and synthesis of cellular material. Today, strains of Rhizobium
are sold to enhance agricultural
productivity and is the subject of considerable
In fact, some cultivars have been developed with the bacterium as a
E. Examples of food legumes:
green bean, plus many other genera and species.
beans are native to
and the Andes.
Rich in protein, also some carbohydrates
Intestinal gas, caused by bacterial breakdown of indigestible (by humans)
complex carbohydrates in colon. Alleviate three ways: long cooking time,
treatment of cooked beans with enzymes
"Beano" is commercial trade name), plant breeding to eliminate complex
carbohydrates. Beans are
not the only food that causes flatulence.
Phaseolus vulgare are
red kidney bean:
considerable production in the United States;
and green beans
Example of Phaseolus lunatus, the
bean or broad bean (Vicia faba): popular in
Some people have genetic defect in an enzyme, suffer from
favism = hemolytic anemia,
when they eat fava beans.
Many different kinds of beans eaten as cooked seeds; or immature pods also
eaten as green beans , since 1700s.
For example the
mung bean (Phaseolus aureus) which is grown for bean sprouts,
or adzuki bean, which is cultivated in Asia
cultivated in the United States with
depending upon the bean.
2. Peas (Pisum sativum):
garden pea; plus
other genera and species. Garden pea is native to Near East.
Rich in protein, carbohydrate.
Immature pod also eaten, as
snow peas or
sugar snap peas.
Peas were subject of Mendel's investigations of genetics.
grown in the United States as a field pea used for livestock, a garden pea,
and as an edible-podded pea.
(Arachis hypogea): Native of South America; introduced to Europe,
from there to Africa, from Africa to U.S. with slave trade.
Rich in oil
Unusual growth characteristic: After fertilization, the flower stalk dips
and grows into the ground, where the pod matures. (Peanuts are called ground
nuts in many parts of the world.)
Uses: Half of U.S. crop for
butter; rest for snack food, candy, peanut oil. Oilcake remaining after
pressing oil is rich in protein, used for animal feed.
4. Soybeans (Glycine
max): Native of China;
into Georgia in 1765. Now
the most valuable
crop in the United States, grown in Midwest and South.
Oil used for
oil, salad dressing, margarine, shortening, mayonnaise.
Oil cake is rich in protein, used for animal feed, also to make textured
vegetable protein (TVP), used as meat substitute for humans, can be spun
or shaped in many ways, flavored to taste like any meat.
Traditional uses in the Orient:
Soy sauce = fermented
soybeans and grain in brine
= soy milk curds
= fermented soybean and rice paste in Japan
= fermented soy cake in Indonesia.
Soybeans also eaten as
Widely used as a health
Oil can be used as diesel fuel, or made into plastic, paint, ink, soap.
A major crop in the United
production increasing rapidly, with
5. Forage legumes: several can be dried and made into hay, usually with grass
for nutritional balance. Examples include:
Some 20 million acres of alfalfa are planted currently in the United States.
spp, true clovers; many species.
clover are found widely introduced, and in many instances naturalized,
in pastures throughout the United States.
are now planted for hay and erosion control, but often are weedy.
6. Kudzu (Pueraria
lobata), an important albeit minor
plant (as a starchy root) in China, is now a major weed in the southeastern
Starch: most widespread storage form of energy in the plant kingdom
Starch is a linear
polymer (chain) of glucose molecules.
Most common starchy crops have a tropical origin.
Many plants have specialized organs for storing starch.
stems [Consult this site for critical information]:
thickened underground horizontal stem, may spread the plant, new shoots grow
from nodes. Examples: ginger, iris.
Tuber = thickened
and rounded organ on a rhizome. Example: potato.
Bulb = short
vertical stem with thick leaves. Example: onion, tulip, daffodil
Corm = short
vertical thick stem, surrounded by thin leaflike scales. Example: gladiolus,
Storage tap root: thickened main root. Examples: carrot, turnip.
Tuberous root: thickened portion of a lateral root. Example: sweet potato,
Important starch crops (besides grains)
Potato (Solanum tuberosum) in the potato family (Solanaceae),
highlands; domesticated 8000 years ago but consumed by humans some 13,000
mya. Staple crop of
the Incas. Grown at high elevations, can be stored dry for months. Chuno
= freeze-dried potato mush; potatoes trampled to squeeze out water, frozen
outdoors; stores dry for years.
Spread to Europe by Spanish conquerors of South America in about 1570; taken
to England from Virginia by Thomas Hariot via
Walter Raleigh and given to Queen Elizabeth in 1590; Hariot and Raleigh
were also involved in the introduction of tobacco. Thought to be poisonous
because other European plants of same family are (nightshade, mandrake, henbane).
First used for livestock feed. Spread from Spain to England and Ireland and
Check out the interviews with Dr. Donald Ugent, an American expert on the
ethnobotany of potato
Potato in Ireland: Population grew to 8 million in 19th century, supported
by potato production. Late blight destroyed crop in 1845-49,
causing famine. 1 million died,
1.5 million emigrated; population never recovered.
Top producers now
China, Poland; note the extensive parts of the world where potato is
Production and uses in the United States: Produced in cool climate states
(Idaho, Washington, Maine). 1/3 used fresh, 1/2 processed into french fries,
potato chips, instant mashed potatoes, potato starch.
Propagation: vegetatively by seed potatoes, either small potatoes (Europe)
or pieces of large potatoes, each piece has an eye (= bud).
Nutrition: 25% carbohydrate, 2.5% protein. Although protein content is low,
the amino acids in it are well balanced for human nutrition. Irish laborers
are said to have eaten no meat, 10-15 lbs potatoes per day as the only source
of carbohydrate and protein.
A popular food today in
B. Sweet potato
(Ipomea batatas) in the morning-glory family (Convolvulaceae):
a tuberous root
of a vine.
Origin in Caribbean; introduced to Europe by Columbus.
Rich in starch; orange cultivars also rich in Vitamin A and
beta-carotene. Requires more tropical climate that white potato. China
produces half of world crop; about 700,000 tons produced annually in the
Mistakenly called yams in U.S., especially if canned.
(Manihot esculenta) in the
family (Euphorbiaceae) :a tuberous root of herbaceous plant.
Origin Brazil and/or Mexico. Also called manioc, yuca (misspelled yucca at
Greatest production tropical Africa, next Asia, next South America (see recent
production figures). Roots can be harvested piecemeal or all at once;
keeps in the ground for long periods. Variously treated by
peoples. On a global basis, cassava is regarded as the one plant between
living and starvation; as a result, its
annual production is closely monitored
Processing to remove hydrogen cyanide (HCN) released when the root is ground:
grinding or grating the roots, squeezing the mush in flexible baskets to
remove juice, or simply prolonged boiling or drying of strips. Cassava is
cooked, eaten as porridge, baked as flat bread, or processed into starch
that can be stored dry (especially in Brazil), used for animal feed, source
of industrial starch.
Bitter and sweet
forms depending on the amount of cyanide and various acids. Eaten in
U.S. as tapioca pudding.
Nutrition: Cassava is 30% starch, very little else nutritionally; poorest
of starchy crops in protein, vitamins. International efforts are underway
to produce improved
Used for a
of purposes as a gluey starch. There is an active research program to
develop low hydrocyanic acid, high yield cultivars capable of surviving in
D. Other starchy crops, all tropical:
(Dioscorea spp.) in the yam family
(Dioscoreaceae): a tuber, throughout tropics. Besides food, used
as source of steroids used to make contraceptive pill and cortisone and
esculenta) in the arum family (Araceae): a corm. Origin southeast
Asia. Used and grown in Hawaii to make poi.
(Musa x paradisiaca, a hybrid cultivar) in the banana family
(Musaceae) and other species: Origin in SE Asia, originally starchy;
sweet banana selected from it. Most cultivars are sterile triploids (hybrids
of diploid and tetraploid), must be propagated vegetatively. Plant is herbaceous,
"stem" consists mostly of leaf sheaths.
Other Sites of Interest:
quick review: Good to do now and then
scientific names of crop plants
of edible plant parts
timebomb: Note the role of plants
An epicurean review
A reference guide to soybean
the Irish famine, 1846-1850
Learn more about the
Inca people and culture
Dr. James A. Duke, formerly with USDA, but now associated with the Department
of Plant Biology at the University of Maryland, has prepared a number of
detailed treatments for economic plants (including folk medicine, ecology,
cultivation, yield data, etc.). Among those considered here are:
Back to BSCI
124 main page
Last revised: Aug 1998 - Barnett