While garlic and onions are small things, one could not imagine cooking without them today. Onions and garlic belong to the Allium genus. Allium, in fact, is derived from the Greek word for garlic. Shallots, scallions, leeks, and chives are also members of the allium family.
For a great breakdown of the different types of onions and how to use them as well as all of the other allium veggies, check out the All About Allium Vegetable link.
http://www.thevegetariansite.com/health_allium.htm
If you have Crohn's Disease, you cannot eat onions or garlic or most of the allium based vegetables. So what do you do then? Many recipes start with a base called a mirepoix. A mixture usually of celery, carrots and onions. Alliums are also usually the base for most stocks. If you are allergic, just don't like the taste or the smell of alliums or have Crohn's disease, Here are some ideas I have found while looking through the Internet.
•Celery is among the most common aromatics.
•Bell peppers are often used in Cajun cooking. Green peppers and celery are a good base for rice dishes or savory stews.
•Carrots are used as an aromatic in French cooking in combination with celery.
•Celeriac, or celery root, is the knobby root of one variety of celery. Peeled and diced, it can be used as an aromatic in sauces or stews.
•Peppercorns: white, pink, or Szechuan pepper can add different flavors to your cooking.
•Cumin's distinctive taste that may work well in some recipes, especially where garlic is used raw.
•Horseradish, freshly grated, can add some of the pungent notes you might otherwise lack.
•Ginger and galangal have distinctive flavors but may be useful in stir-fries as aromatics.
So here's to eating stinky flowers! :)