Calendula ( ), is a genus of about 15–20 species of annual and perennial herbaceous plants in the daisy family Asteraceae that are often known as marigolds.
 They are native to southwestern Asia, western Europe, Macaronesia, and the Mediterranean.
 Other plants are also known as marigolds, such as corn marigold, desert marigold, marsh marigold, and plants of the genus "Tagetes".
Serissa is a genus of flowering plants in the family Rubiaceae, containing only one species, Serissa japonica.
 It is native to open sub-tropical woodlands and wet meadows in southeast Asia, from India, and China to Japan.
 It is commonly called the snowrose, tree of a thousand stars, or Japanese boxthorn; and was formerly called Serissa foetida.
 'Foetida' referres to the unpleasant, vomit-like, odour that the trees give off if their leaves are pruned or bruised.

Question: Which contains more species, Calendula or Serissa?
Answer: Calendula