Perennial vegetables ; )

Kale keeps on going, my plants are almost two years old now. You can cut the main stem back and new ones will sprout from the base.

Lima beans will keep on going for a long time too. I have a few plants that are almost three now.

Eggplant and cherry tomatoes will keep going for a long time but i like to replant at least once a year.

You might also want to check out pipinola and asparagus.

It makes sense to take advantage of perennial vegetables in Hawaii. Hope others chime in with more suggestions ; )

Sorry, just noticed that you are looking specifically for greens suggestions.

How about pipinola shoots, sweet potato vines or taro leaf? All of these need to be cooked, though.

Collards will stay alive for a really long time. Just pick the lower leaves and leave the top ones growing.

Leaf lettuce can be grown for awhile, too. Pick the lower leaves and leave the tops growing.

Water cress just keeps growing once you get it established.

There are also moringa trees although that's more of a flavoring than a green.

For greens that you could use fresh for salads and are perennial:

Okinawan Spinach
Thai Basil
Malabar Spinach (Some people eat it raw)
Chayote (the leaves shoot could be used fresh)

This is the plants that I have experience growing and last very long. The Okinawan Spinach is growing for more than three years I believe; and when it grows leggy, I trimmed and used some of the pruning to grow new plants.

I thought all basil are annual, but when I grew the Thai Basil, it lasted for more than a year now, and it still growing strong! It branched so much that it looked like a single ball shaped topiary in my garden--I usually pruned it a lot, the prunings are either eaten when we make Pho soup, or goes to compost bin, it is that productive. The one I have has a smaller leaves than the usual large Thai Basil leaves found in Farmer's Market. I also has success growing new plant from the cuttings.

The Malabar Spinach I heard could be eaten raw, but my mom usually prepare it by blanching, then adding tomatoes and seasonings. This plant requires trellis to grow because it is vining plant. It also the same for Chayote leaves, people eat the raw leaves shoots, but my mom prepare it like the Malabar Spinach. This is also a vining plant and it is very prolific and gives you edible fruits, too!

There are other plants/herbs that you could used for salads:

Green Onion (When you buy green onion, save the white part and the roots, and plant it. It will grow new leaves for you to harvest.)

Chives are also perennial, this herb has been growing in my large pot for more than five years.

I also acquired new lush Mexican Tarragon last month that is currently blooming edible bright yellow flowers, I used to have this over a year ago, but It was neglected and it died. This is also a perennial. I have the true French Tarragon, but it is doing poorly in my garden.

I have Chocolate Mint that is growing invasive, but I don't mind because it's easy to control in my experience. Add this to your salads to add some fresh taste to it.

Kaffir lime is also a good plant to have for salad. The leaves are very thinly slice and will add that citrus-like taste, it's not the taste of a citrus rind or the juice, it's more subtle. I mainly use this for Pho soup.

I hope you acquired some or all the plants I mentioned! With a bit of TLC, these plant will last for a very long time, but do propagate most of it as an insurance and to give to friends.

One of the easiest to grow greens for hot areas is New Zealand spinach. You can grow it in pots or in ground and it will become a perennial. Alongside upland cress it is my favorite green.

We've discovered beet greens are pretty tasty. We planted a new raised bed garden just after Christmas and the beet tops are about as tasty as the roots. I'm thinking they would almost be a good substitute for taro leaf in laulaus. We steam them and add a bit of balsamic vinegar or a drizzle of olive oil.

I am having great luck with my spinach. I planted the bottom part of a bunch I got from the farmers market in a pot about 4 months ago and it's been growing like crazy since. I have enough for a side dish(for 2 people)about once a week from just one plant in a 6 inch pot. It is hot, dry and full sun everyday where I am and I water at least twice a day. I discovered recently that radish leaves are quite tasty sliced thin and tossed with stuff and they grow fast but a one time deal.

I grow lettuce and just pick the outer leaves; I never harvest the whole head unless it looks like it's about to bolt. Often I'll go through and pick all but the two most inner leaves and make a salad. Within a week, it's regrown a bunch of leaves and is ready to pick again for another salad.

Other greens I'm growing where you can harvest the outer leaves and let the plant grow more:

-Kale (I'm growing 4 different varieties)
-Chinese Broccoli
-Arugula
-Endives
-Beets (can eat the greens, and the thinnings, especially when young)
-Many kinds of lettuce
-Cauliflower (can eat leaves- taste a lot like kale)
-Collards
-Swiss Chard (as you mentioned)
-Celery (not sure if it will form thick stalks in this climate, like in the grocery store, but the stems and leaves taste just the same)
-Cilantro
-Parsley
-Basil (grows like crazy here and takes over everything)

I usually prefer the brassicas like kale and collards cooked a bit (lightly sauteed with a little salt and lemon: yum!), but you can eat them in a salad if you want, especially young and tender. I like to plant those guys really thick, then gradually thin them out and eat the tender young thinnings to make room for the rest to grow to full size.

Hope that helps! Fresh salad from your own garden; there's really nothing like it!