Plants and People

Major Families II

Poaceae - The Grass Family

Humans devote more than 70% of the Earth’s farmlands to the production of cereal grains

Grasses provided at least 50% of the world’s caloric intake

Some anthropologists are of the opinion that the use of cereal grain was a prerequisite for the formation of a civilization

Vegetative Characteristics

Grass Inflorescence The spikelet is the basic unit of grass inflorescence with one or more florets making up the spikelet. The spikelet is subtended by two sterile bracts known as glumes. The glumes define the spikelet, they and everything above them make up the spikelet

Floret

Glumes

Spikelet

Floral Morphology

• The perianth has been reduced to structures colled lodicules, located at the base of the ovary (these may be absent)

• The mature ovary (fruit) is termed grain or caryopsis

• Each flower is enclosed by two fertile bracts, with the larger bract, the lemma enclosing the usually smaller bract termed the palea

• The tip of a glume, lemma or palea may be extended into a bristle-like structure called an awn

• The lemma, palea and the flower make up the floret

Flowers of the grass family are highly reduced and non-showy and are described using unique terminology

Floral MorphologyAn oat spikelet:

glumes

anthers

lemma 2

lemma 1

awn 1

awn 2

palea 1

palea 2

stigma

The Bean Families

Fabaceae

Caesalpiniaceae Mimosaceae

Legumes

The Bean Families

• Everyone agrees that the legumes form a coherent whole based on the presence of a single carpel that matures into a legume.

•They can be divided into three groups based on the arrangement and structure of the androecium and perianth, collectively called the androperianth.

•The question is whether to :--treat them all as a single family Fabaceae (broad sense) with three subfamilies or --treat them as separate families in the order Fabales. This is what we shall do.

Fabaceae (strict sense)Flowers in Fabaceae are zygomorphic and papilionaceous (butterfly-like). The corolla is consists of 5 petals: a banner, 2 wings, and a fused keel. The banner is exterior to the wings.

Fabaceae

The fused keel encloses the unique androecium, 10 stamens in 9 fused+ 1 free arrangement (this is termed diadelphous.) The stamens surround the style but are not fused to it.

Caesalpiniaceae

banner

wings

keel petals(not fused)

Flowers in the Caesalpiniaceae Family are zygomorphic and papilionaceous (butterfly-like). The corolla is consists of 5 petals: a banner, 2 wings, and 2 un-united keel petals. There are 10 stamens that are free and often unalike. The banner is usually located interior to the wings.

Mimosaceae

Flowers in the Mimosaceae are actinomorphic. Many tiny flowers, each with long, showy stamens, are grouped into globose or elongated inflorescences. These stamens are the showy part of the flower, rather than petals. The corolla is either free or fused.

stamens

corolla

calyx

an individual flower

Lab Today

• Make sure to examine the oat spikelet dissected for you under one of the microscopes

• Sketch your own diagram of the oat spikelet, labeling the important terms, and make sure you understand the different parts of the spiklet!

• Compare the sample legume material with information given to you in lecture, paying close attention to the arrangement and structure of the androecium and perianth

• Examine the legumes and grains, filling out the table provided for today’s lab