Here is a list of plant families and common crops in each one. Learning the plant families makes companion planting easier. You start to realize that plants within the same family tend to share common companion plants, pests and diseases. Knowing the families aids in crop rotation and can help you plan a garden.
It still amazes me which family certain crops are in. Can you believe lettuce is in the same family as sunflowers and artichokes? Notice how many fruit trees are in the same family. That explains why there are so many common fungus issues between them.
LAMIACEAE FAMILY
Mints, Basil, Rosemary, Thyme, Oregano, Sage, Lavender
SOLANACEAE ( Nightshade) FAMILY
Tomatoes, Tomatillos, Eggplants, Peppers, Okra, Potatoes
UMBELLIFERAE FAMILY
Parsley, Carrot, Parsnips, Celery, Fennel, Cilantro/Coriander
ASTERACEAE ( Asters) FAMILY
Sunflower, Jerusalem artichoke, Lettuce, Endive, Artichoke
BRASSICACEAE ( Cole Crops) FAMILY
Broccoli, Brussels sprouts, Cauliflower, Cabbage ,Kale, Collards, Radishes, Kohlrabi, Turnip, Mustard
AMARYLILDACEAE ( Onion) FAMILY
Onion, Leeks, Chives, Garlic, Asparagus
ROSACEAE FAMILY
Apples, Pears, Quinces, Almonds, Peaches, Apricots, Plums ,Cherries, Strawberries, Blackberries Raspberries
POACEAE ( Grasses) FAMILY
Corn, Millet, Rice, Barley, Wheat, Rye
FABACEAE (LEGUMES)FAMILY
Peas,Runner beans,Bush beans,Fava beans, Garbanzo beans,Peanuts
Amaranthaceae/ Goosefoot Family
Beet,Spinach,Chard,Quinoa,Orach
CUCURBITS
Cucumbers,Zucchini, Summer Squash,Watermelon,Musk Melon,Pumpkin,Gourd
CONVOLVULACEAE( Morning glory) FAMILY
Sweet potatoes