Salviniaceae (or formerly Salviniaceæ) is a family of heterosporous ferns in the order Salviniales.
 The Salviniaceae contain the two genera "Azolla" and "Salvinia", with a total of ca 20 known species.
 "Azolla" was previously placed in its own family, Azollaceae, but recent research has shown "Azolla" and "Salvinia" to be sister genera with the likely phylogenic relationship shown in the following diagram.
Azolla (mosquito fern, duckweed fern, fairy moss, water fern) is a genus of seven species of aquatic ferns in the family Salviniaceae.
 They are extremely reduced in form and specialized, looking nothing like other typical ferns but more resembling duckweed or some mosses.
Sinowilsonia is a monotypic genus of plant containing the single species Sinowilsonia henryi.
 It is endemic to China.
 It is threatened by habitat loss.
Azolla primaeva is an extinct species of "water fern" in the Azollaceae family known from Eocene fossils from the Ypresian stage (ERROR!
 Start of period Ypresian unknown, perhaps because it was mis-spelt or because it is missing from . )
, found in southern British Columbia.
Azolla filiculoides (water fern) is a species of "Azolla", native to warm temperate and tropical regions of the Americas as well as most of the old world including Asia and Australia.
Azolla cristata , the Carolina mosquitofern, Carolina azolla, or water velvet, is a species of "Azolla" native to the Americas, in eastern North America from southern Ontario southward, and from the east coast west to Wisconsin and Texas, and in the Caribbean, and in Central and South America from southeastern Mexico (Chiapas) south to northern Argentina and Uruguay.
Pilularia americana, the American pillwort, is an unusual species of fern.
 The fronds essentially consist of the stems only, any form of flattened laminae having been lost.
 It is in the aquatic fern family Marsileaceae, and is related to the water clovers and also to "Azolla" and "Salvinia".
Azolla pinnata is a species of fern known by several common names, including mosquitofern, feathered mosquitofern and water velvet.
 It is native to much of Africa, Asia (Brunei Darussalam, China, India, Japan, Korea, and the Philippines) and parts of Australia.
 It is an aquatic plant, its frond floating upon the surface of the water.
 It grows in quiet and slow-moving water bodies, because swift currents and waves break up the plant.

Question: Which has more species, Sinowilsonia or Azolla?
Answer: Azolla