Arugula like garden cress has irregular leave forms, especially when the grow taller and bigger. Same goes for cilantro.
I don't knw about the difference in taste. But in cold weather vegetable have less moisture contents and are chewy.

I agree with Seysonn. Size of the plant seems to affect the shape of Arugula leaves, along with the season.

Personally, I've never thought of the "grooved" leaves as being 'less tasty'. I think that when it's close to bolting the leaves are a bit spicier, but in cool weather, arugula is usually sweet and tender.

-Mark

Now that you mention it the tasty would have been more accurate as less tough. The leaves are not as tender as the more evenly oval leaves. There is also less leaf and more stem.

You may have the more lobed sylvetta (wild arugula) as opposed to the regular smoother developed variety. Did you plant from the same pack, or different packs?

I was going to say the same thing as glib. If you just plant a generic packet of arugula there will be some natural variation of the leaves, especially from different seed sources/suppliers. If you want uniformity you have to choose a cultivated variety.

Rodney

I got these in a 4 pack at my local nursery. Maybe they are a different variety than I had in the past. I think that I've heard Rocket is best. One of my friends who is from Israel said their arugula leaves are much bigger than what we have here. I should just plant my own seeds next time but it was so hot at the end of the summer I didn't get around to pulling up the summer crops so I went the easy route.

I have found great differences in leaf shapes and in taste from different packets of seeds. If you find a variety you like, then stick with that seed. If you don't like it, yank it up and try different seed. What is in the photo doesn't look like sylvetta to me -- my sylvetta has always looked almost feathery with very small, deeply indented leaves.

Also, if you really like a variety you can let it go to flower (the flowers are also edible) and to seed, and just leave it alone and you'll probably end up with a self seeded patch of arugula you like. (works most of the time -- though sometimes it doesn't come true.)

If you're buying seedlings, just grab a leaf while no one is looking and taste it to see if you like it :)

Johnny's selected seeds has a number of different kinds of arugula, with descriptions of each, and their seed is true to form every time (I'm had some companies where one year it's great, the next year not.)

Yes, there are different breeds. Generally the more lobed the hotter. None is really "better": in a dish that requires spice, or for pesto, the lobed ones are best. Even for mixing with tomatoes lobed is best. For straight salads we mostly prefer the milder rocket. You can make it milder with more watering, partial shade, and growing season.

Lobed varieties are smaller than cultivated varieties, but culture matters just as much as variety when it comes to size. The very same bed and very same pack will give me different size of plants depending on season and watering.