Poaceae (Gramineae)

Poaceae (Gramineae)

Organic Seed

Spring 2004

Poaceae

One of most important from human food500 genera and 8,000 species

Grass structure

Inflorescence Spikelet of Poaceae

Generalized grass flower

Important cereals

A. Oats (Avena sativa); B. Barley (Hordeum vulgare);

C. Bread Wheat (Triticum aestivum); D. Rye (Secale cereale).

A. Bread wheat (Triticum aestivum); B. Rye (Secale cereale);

C. Triticale (Triticosecale).

Wheat and rye are crossed together to produce the hybrid triticale.

http://waynesword.palomar.edu/ecoph12.htm

Rice (Oryza sativa)

A. Grain-bearing spikelet showing a pair of slender basal bracts (glumes)

and the stalk (pedicel). B. An empty spikelet with the lemma and palea

slightly separated from each other. These two leathery bracts enclosed

the grain or caryopsis. C. A grain (caryopsis) removed from spikelet

Maize or Corn (Zea mays)

Strawberry corn, popping corn, Indian corn and pod corn.

Progenitor: teosinte.

I. ORIGINA. S. Mexico ‑5000 BC

Developed from teosinte (UWis- Hugh Iltis)

Modern-

increased

apical

dominance of

tassel--

only 1 or 2

ears and few

tillers

B. Ohio valley by 800's AD

C. Columbus to Spain 1493; Africa & Asia within 50 years

D. Corn belt dent (northern flint x southern dent) spread in 1850's

Teosinte (Zea mexicana)

A. Male Inflorescence (Tassel)

B. Female Inflorescence (Ear)With Outer Husk & Silk

C. Ear With Husk Pulled AwayExposing A Row Of Grains

D. A Leaf Pulled BackExposing Two Ears

E. Leaf (Blade)

Teosinte (Zea mexicana) showing pollen-bearing tassel (left) and a

female ear with silk (right). This is truly a miniature version of the

modern corn plant (Zea mays). Compare this tiny ear with the

following image of a modern ear of corn.

Modern corn

Silk: red, threadlike styles

and the green, leaflike husk enclosing

numerous ovaries of female flowers which

develop into the grains.

II. BOTANY (OVER 300 RACES)A. Monoecious (tassel-male;

cob-female) (that and being x-pollinated greatly facilitates hybrid seed production)

B. 25 million pollen grains/plant (50,000 for each one that produces a grain)

C. Husks are modified leaves (allow harvest in rainy season)

Corn female flower

Corn male flower

The seed spike of teosinte consists of a single row of grains.

Each grain is enclosed in a hard fruit case (called a cupule)

and a pair of papery glumes. This spike = ear of modern corn.

Tunicate Mutation: The grains are enclosed in a pair of husklike glumes

(without the hard outer cupule) from which they can be threshed easily.

Further selection by pre-Columbian farmers could have reduced the size

of the tunicate glumes and resulted in ears with many rows.

Close-up view of pod corn showing papery glumes enclosing the grains

F. Many endosperm types developed by selection

1. DENT (USA, N. Mexico): large kernels with central core of floury endosperm which shrinks upon drying

2. FLINT (Argentina, Africa): large smooth kernels with mainly hard endosperm but with small floury center

A. POP (IO,NE, Central Mexico): small smooth kernels with hard endosperm

Endosperm types continued3. SWEET (MN, WI): Large

kernels with carbohydrates

stored as sugars

4. FLOURY (Andean countries): large smooth kernels with floury endosperm

5. WAXY (Asia) Normally maize is 27% amylose (straight chain) and 63% amylopectin. Waxy corn has 100% amylopectin. Used to substitute for cassava starch.