Question: Which genus of plants is within the Asteraceae family, Tithonia or Hymenocallis?
Context: Hymenocallis (US) or (UK) is a genus of American plants in the amaryllis family. Tithonia is a genus of flowering plants in the sunflower tribe within the Asteraceae family. Tithonia diversifolia is a species of flowering plant in the Asteraceae family that is commonly known as the tree marigold, Mexican tournesol, Mexican sunflower, Japanese sunflower or Nitobe chrysanthemum.  It is native to Mexico and Central America but has a nearly pantropical distribution as an introduced species.  Depending on the area they may be either annual or perennial.  It has shown great potential in raising the soil fertility in soils depleted in nutrients.  Originating in Mexico; research has shown its potential in benefiting poor African farmers.  This plant is a weed that grows quickly and has become an option as an affordable alternative to expensive synthetic fertilizers.  It has shown to increase plant yields and the soil nutrients of nitrogen (N), phosphorus (P), and potassium (K). Leontopodium is a genus of plants in the Asteraceae family (which also includes daisies and sunflowers).  The genus is native to Europe and Asia.  The fuzzy and somewhat stocky "petals" (technically, bracts) could be thought of as somewhat resembling lions' paws —hence the genus name combining "léōn" (lion) and "pódion" (foot). Simsia is a genus of flowering plants in the sunflower tribe within the daisy family.  It includes annuals, herbaceous perennials, and shrubs.  They range from the western United States south through Central and South America to Argentina, with the center of diversity occurring in Mexico.  The genus is named for British physician and botanist John Sims (1749–1831).  Although some species are relatively rare, others have become common weeds that line the roadsides and fields of Mexico, often forming dense stands mixed with "Tithonia" and other Asteraceae.  Some species are known by the common name bushsunflower. Polydora is a genus of plants belonging to the Asteraceae family, consisting of some 8 species.  The genus is related to "Vernonia" and is native to Sub-Saharan Africa. Anaphalis is a genus of herbaceous and woody flowering plants within the Asteraceae family, whose members are commonly known by the name pearl or pearly everlasting.  There are around 110 species with the vast majority being native to central and southern Asia.  There is one species native to North America that is fairly well known and popular in cultivation, namely the western pearly everlasting ("Anaphalis margaritacea"). Taraxacum ( ) is a large genus of flowering plants in the family Asteraceae which consists of species commonly known as dandelion.  They are native to Eurasia and North America, but the two commonplace species worldwide, "T. officinale" and "T. erythrospermum", were introduced from Europe and now propagate as wildflowers.  Both species are edible in their entirety.  The common name dandelion ( , from French "dent-de-lion", meaning "lion's tooth") is given to members of the genus.  Like other members of the Asteraceae family, they have very small flowers collected together into a composite flower head.  Each single flower in a head is called a floret.  Many "Taraxacum" species produce seeds asexually by apomixis, where the seeds are produced without pollination, resulting in offspring that are genetically identical to the parent plant. The red sunflower or Mexican sunflower (Tithonia rotundifolia ) is a plant in the Asteraceae family, which is native to the warmer and moister parts of North America. Athroisma is a genus of plants in the Asteraceae family first described as a genus in 1833.  It is native to East Africa and Madagascar.
Answer: Tithonia