There are over 400 species of gentian plants, and they come in a wide range of sizes. Some are indeed quite tall, reaching up to 3 feet or more, but others are much smaller, only a few inches high.

The height of a gentian plant is influenced by several factors, including:

* Species: As mentioned above, different gentian species have different growth habits. Some are naturally tall, while others are naturally short.

* Growing conditions: Factors like sunlight, water, and soil nutrients can affect the growth of any plant, including gentians. For example, a gentian growing in a sunny location with ample water and rich soil might grow taller than one in a shady location with poor soil.

* Genetics: Like any plant, a gentian's genetic makeup influences its growth potential. Some individuals within a species may simply be genetically predisposed to grow taller than others.

So, while some gentians do grow tall, it's not a universal trait. Many gentian species are quite small, and even within a species, the size of individual plants can vary significantly.