Smooth-leaf spinach, also known as flat-leaf spinach, has dark green, smooth leaves. This type of spinach is generally more tolerant to heat and disease, making it a good choice for growing in warmer climates. The leaves of smooth-leaf spinach are also more delicate and tender, making it a great choice for salads or sandwiches.

Savoy spinach, on the other hand, has crinkly, dark green leaves. This type of spinach is generally more cold-tolerant and can withstand frost, making it a good choice for planting in the fall or early spring. The leaves of savoy spinach tend to be more resilient and have a stronger flavor, making it a great choice for cooking, such as sautéing or using in soups or stews.

Another type of spinach is semi-savoy spinach, which is a hybrid of smooth-leaf and savoy spinach. This type of spinach is a cross between the two and has the best of both worlds. It has the delicate, tender leaves of smooth-leaf spinach and the hardiness of savoy spinach.

In terms of seed variety, there are also several cultivars available that have been bred for their specific characteristics such as disease resistance, heat tolerance, or early maturity. Some popular cultivars are ‘Bloomsdale Long Standing’, ‘Corvair’, ‘Space’, ‘New Zealand Spinach’ etc.

It’s worth to note that different spinach types and varieties have different growing conditions and needs, so it’s important to choose the right type and variety for your climate and growing conditions.