Which of the following junipers is a 'Nana' variety?

The 'Nana' variety of junipers refers specifically to Juniperus procumbens, commonly known as creeping juniper. This variety is characterized by its low, spreading habit and dense foliage, making it a popular choice for ground cover in landscaping. The 'Nana' variety is particularly favored due to its ability to thrive in a variety of soil types and its drought-resistance once established.

In contrast, the other species listed either do not have a 'Nana' variety or are not as widespread in use for ground coverage. Juniperus sabina, also known as savin juniper, has a more upright growth habit, while Juniperus squamata, or flattop juniper, has a different growth form and spread. Juniperus communis has several varieties, but it is not commonly referred to as 'Nana' and is typically taller and more traditional in shape compared to the creeping juniper. Therefore, Juniperus procumbens is the correct choice for identifying the 'Nana' variety.