Cucumber and squash leaves

As a general thing, it's not a good idea to assume specific similarities- such as edibility (well, it's a word now)-based on plant families; the families are based largely on physical traits of the reproductive system and don't necessarily imply parallel chemistry. It does, however, form a reasonable basis for inquiry (which is what you actually did)- you do find a lot of berries in the rose family, culinary herbs in the labiates etc.

At an Asian foods store I found blanched frozen bitter melon leaves from the Filipines. They come from a plant that makes a very very bitter fruit that looks like a cucumber. The fruit is supposed to be a good treatment for diabetes but I don't know why. The fruit may be cooked with a large quantity of sweeter vegetables like carrots and winter squash. The leaves came in a small package (8 oz) blanched like frozen spinach and were bitter but not quite as bitter as fresh (which the store carries only sometimes). Seems like with the bitterness and texture a little would go a long way. With any green I experiment with the cooking time. I want it not too mushy and to keep some bright green color (not olive green). Usually I make sure to add greens to water that is boiling wildly or to a pot or pan that is already hot and to cook just long enough to get the texture and color I want. Then I stop cooking by adding something frozen like frozen peas or even a vegetable grain or bean that I have previously cooked and frozen myself, like white navy beans, black beans, cut up squash cubes, cut up sweet potato (not real potato potatoes since they get a weird texture when you freeze them), cooked sorgum etc. I say experiment with the cooking time and see what suits your taste.

Idea for zucchini leaves from an article by Faith Wllinger in The Atlantic:

"If I had access to a garden, I'd pick the tender first leaves, zucchini tendrils, and stew them in extra virgin with garlic, zucchini chunks, and chopped flowers, a dish I've enjoyed in Campania, Puglia, and Sicilia. Beg your source to pick small females and harvest male flowers and maybe even some tendrils. And enjoy zucchini at its best, in season."

Pumpkin and squash leaves - the young shoots and young leaves - are great cooked in coconut cream/milk with onion, a bit of fresh grated ginger and salt to taste. I use chicken broth and coconut powder (not coconut flour; but packaged coconut milk powder found in Asian grocers) or fresh grated and squeezed cream from shredded coconut. Sometimes I will put a chicken piece (neck, back or wing) in water, make a broth from it, add coconut powder (which is sometimes rather lumpy, so use a fork or spoon to break it up), THEN add the pumpkin or squash greens (or any kind of greens) and ginger to the broth and cook only a little bit. You want them to remain bright green so as to get the most nutritional value from them. Even though these greens and young stems are a bit fuzzy, the flavor is really nice. This is how they are cooked in coastal areas of Papua New Guinea. Yum!

yes you can eat squash and pumpkin leaves. saute with onion, garlic oil, turmeric and red chilil powder. cook for 10 min. if you wish to add shrimp or potato it will be more delicious.

Cucumber leaves are kinda fuzzy and un-appetizing. Striped cucumber beetles love them, however.

In Nigeria, we sautee pumpkin leaves and combine it with ground egusi (melon seeds, or sub crushed peanuts), to make a stew. Sometimes, we sautee it with tomatoes, onions and scotch bonnets, season with maggi stock cubes, salt, dried crayfish (or shrimps)

Cucumbers: Stems and leaves of young plants are edible in moderation. Cucumber leaves have emetic properties (they induce vomiting) when taken in large quantities. Fruits, seeds, and skin are all fully edible. via: http://www.gardensablaze.com/GardenQA/Edibles.htm

It doesn't sound like a good idea to eat cucumber leaves!

A friend of mine spent a year in Kenya while in the Peace Corp. He said they would cook pumpkin leaves, but didn't supply a recipe. I suspect you would be able to eat them, too.