Basil is an important culinary herb. It comes in many varieties throughout the world, including the sweet basil often seen in Western cuisine and the Thai basil (known in Taiwan as jiu ceng ta) widely used in Asian cuisine.
羅勒是製作料理的重要香草，依地區又分成許多品種，包括歐美料理常見的甜羅勒，以及大量運用於亞洲料理的九層塔。
Jiu ceng ta literally means “nine-story padoga,” used to refer to the varieties cultivated in Taiwan. Thai basil has a stronger aroma and is commonly used in Taiwanese style stir fries and snacks. It goes well with spicy, robust dishes.
「九層塔」為台語，用來指稱台灣栽培的羅勒品種，香氣比較濃厚，普遍用於台式熱炒、小吃料理中，適合與辛辣、重口味的菜肴搭配。
Sweet basil is the most common type of basil used in Western cuisine. It looks similar to Thai basil, but its leaves are rounder and its taste lighter and subtler, with a hint of sweetness to it. One classic way to cook it is to mix sweet basil with olive oil, garlic, pine nuts and seasonings to make Italian pesto.
而西餐料理中最常使用的羅勒則是「甜羅勒」，外型類似九層塔，不過甜羅勒的葉片比較圓胖，且口味清爽、細緻不少，帶有些許的甜味。最經典的料理方式是把甜羅勒與橄欖油、蒜頭、松子及調味料混和做成義大利青醬。
Sweet basil and Thai basil are of different types: they have different flavors and hence are suitable for different dishes. If you were to make pesto with Thai basil, its taste would turn out to be too astringent and too strong. So next time you fancy making a genuine pesto, be sure to tell the vendor that you want to buy sweet basil.
兩種羅勒的品種、風味不同，適合不同的料理，所以若把台灣的九層塔拿來製作青醬，口感就會比較澀，氣味也過於強烈。所以下次如果想製作正統的青醬，採買時記得特別跟老闆說明，你要的是「甜羅勒」！
Source article: http://www.taipeitimes.com/News/lang/archives/2017/08/02/2003675730