Which plant is commonly known as sand spur and has finely dissected leaves and small yellow flowers?

The plant commonly known as sand spur is indeed spur weed. This plant is characterized by its finely dissected leaves, which give it a unique appearance compared to other common weeds. Its small yellow flowers are also a distinguishing feature. Spur weed, or its scientific name, can often be found in sandy areas and is notorious for its prickly seed heads, which can attach to clothing and skin, hence the name "sand spur."

In contrast, cudweed, dandelion, and false dandelion each have their own distinctive characteristics. Cudweed typically has a grayish appearance and is more commonly associated with dry or disturbed areas. Dandelions are recognizable by their broad, serrated leaves and large, bright yellow blooms that become fluffy seed heads. False dandelion may resemble true dandelions but lacks some of the defining features and habitat preferences. Therefore, the features outlined for spur weed make it the clear choice for the question at hand.