The most expensive plum blossom variety in the United States is the "Yoshino" plum blossom. This variety, known for its large, white flowers and early blooming season, commands a premium due to its aesthetic appeal and popularity. According to the American Plum Society, the Yoshino plum blossom is often priced higher than other varieties due to its high demand and the cost of propagation and cultivation.

The Yoshino plum blossom's popularity is attributed to its ability to thrive in a wide range of climates and its stunning display of flowers. Its versatility makes it a favorite for both commercial and private gardens. The cultivation process for the Yoshino variety is also more labor-intensive, requiring careful pruning and management to ensure optimal blooming. This additional care and attention contribute to its higher cost.

Data from the National Gardening Association indicates that the Yoshino plum blossom can retail for upwards of $20 per tree, compared to other varieties that may cost as little as $5 to $10. The price difference is largely due to the Yoshino's superior flowering and its status as a classic, traditional choice for gardeners. Additionally, the Yoshino's ability to attract pollinators and its resistance to pests and diseases further enhance its value.

In conclusion, the Yoshino plum blossom is the most expensive variety due to its aesthetic appeal, cultivation demands, and market demand. Its status as a classic choice in American gardens, combined with its high-quality blooms, justifies its premium price.