All the zinnias in the photos were raised from seed.
Their stems may be more angular than that of dahlias. Their leaves may be less lush, but they are not as needy or fussy. Their stems are not hollow, and when cut for the vase do not look maimed. The color range is similar and they are easily raised from seed by anyone who puts them in the dirt. To make them branch one need only to pinch down the central leader.
Also blooming – Cosmos “Seashells”.