Rye is a hardy grass that is best known for being one of the worlds leading cereal crops. It can be used as a substitute for wheat in baking, or a substitute for hay as livestock bedding. It is known for being a very hardy crop, capable of growing and thriving in difficult climates.
Rye is an annual grass that is dark green with a hue of blue in it, and it's grain ranges from light brown to dark gray. They can be anywhere from 3-8 feet tall, with the grain being a good half inch long. Also, they have long 6 inch spikes, that have lots of 2-flowered spikelets. And like most other grasses, it consists of the following vegetative and floral structures: peduncle, culm node, culm, leaf blade, leaf sheath, auricles, ligule, crown, stolon, rhizome, tiller, flag leaf, meristem, collar region, blade (lamina), collar, auricles, and sheath.
Rye, like all grass, reproduce two different ways. 1. Rye has stolons that grow out sideways off the plant and reach out to create new culms. Then these culms live off the parent plant until they can survive on their own. 2. Rye has florets that grow together in spikelets. The flowers produce spores, that pollinate other flowers. This process then produces seeds, which then grow into another grass plant. This way of reproducing is universal in all grasses. 
Rye is used for many different things. But when used for baking or for food, it is second in choice to wheat. Wheat and rye are the only two grains suitable for making bread. However, wheat tastes much better and is easier on the stomach. So why use rye? Rye can grow where wheat cannot. Rye is capable of growing during harsh winter climates. It can grow in the short time during the day when the sun is out and raises the plant's temperature to above freezing. It can even grow with light snow on the ground. Also, it grows very well in high altitudes, where wheat can't grow. 
Rye can be used for many different purposes. It can be used to make rye bread by using it similar to wheat. It can also be used to make rye whiskey. Another use for rye is to use it as livestock feed. Or it can be used for livestock bedding as a substitute for hay. In Europe it was widely used to make pumpernickel bread; a dark brown bread made wholly from unsifted rye flour. Along with wheat, it is the only other grain suitable for making a loaf of bread. However, it lacks the elasticity of wheat, so it is often blended in a mixture with wheat flower when used for baking. 
-  BMC Plant Biology
-  Henriette Kress. 1995-2009
-  Encyclopedia Britannica
-  Gramene
-  Wikipedia