What is a defining feature of plants from the Umbelliferae family?

A defining feature of plants from the Umbelliferae family, also known as the Apiaceae family, is their hollow stems. This characteristic is common among many species in this family, which include well-known plants like carrots, parsley, and celery. The hollow stems can aid in the transport of nutrients and water throughout the plant, contributing to their overall structure and stability.

The other options do not accurately characterize the majority of the Umbelliferae family. While some may display thick roots, such as carrots, it isn’t a defining feature across the entire family. Solitary flowers are not typical; instead, members of this family are known for their distinct cluster of small flowers that form an umbrella-like structure, which is where the name "Umbelliferae" originates. A spreading growth habit varies among species but is not a unique characteristic of the family as a whole.