Question: What is a genus of about 15–20 species of annual and perennial herbaceous plants in the daisy family Asteraceae, Collomia or Calendula ?
Context: Aldama is a genus of flowering plants in the daisy family.  The genus was originally described to include one (later two) species of subtribe Helianthinae that were characterized by having pales that tightly enclosed the cypselae (achenes) (see Feddema, 1971).  Recent molecular phylogenetic studies (Schilling and Panero 2011) showed that these species are within a large group that were formerly classified in the genus "Viguiera", and "Aldama" has been expanded to include a total of 118 species.  "Aldama" is characterized by having a perennial herbaceous habit, a pappus usually of awns and scales, and a multiseriate involucre. Abronia, the sand-verbenas or wild lantanas, is a genus of about 20 species of annual or perennial herbaceous plants in the family Nyctaginaceae.  Despite the common names, they are not related to "Verbena" (vervains) or lantanas in the family Verbenaceae.  They are closely allied with "Tripterocalyx". Senecio squalidus, known as Oxford ragwort, is a flowering plant in the daisy family Asteraceae.  It is a yellow-flowered herbaceous plant, native to mountainous, rocky or volcanic areas, that has managed to find other homes on man-made and natural piles of rocks, war-ruined neighborhoods and even on stone walls.  These habitats resemble its well drained natural rocky homeland.  The plants have spread via the wind, rail and the activities of botanists.  The travels and discriminative tendencies regarding propagation of this short-lived perennial, biennial, or winter annual make it a good subject for studies of the evolution and ecology of flowering plants. Herbchronology is the analysis of annual growth rings (or simply annual rings) in the secondary root xylem of perennial herbaceous plants.  While leaves and stems of perennial herbs die down at the end of the growing season the root often persists for many years or even the entire life.  Perennial herb species belonging to the dicotyledon group (also known as perennial forbs) are characterized by secondary growth, which shows as a new growth ring added each year to persistent roots.  About two thirds of all perennial dicotyledonous herb species with a persistent root that grow in the strongly seasonal zone of the northern hemisphere show at least fairly clear annual growth rings. Lopholaena (from "lophos", a crest, and "chlaina", a cloak) is a genus of perennial shrubs and herbaceous plants in the family Asteraceae.  About 20 species occur from tropical to southern Africa. Galanthus (snowdrop; Greek "gála" "milk", "ánthos" "flower") is a small genus of about 20 species of bulbous perennial herbaceous plants in the family Amaryllidaceae.  The plants have two linear leaves and a single small white drooping bell shaped flower with six petal-like (petaloid) tepals in two circles (whorls).  The smaller inner petals have green markings. Collomia is a genus of flowering plants in the family Polemoniaceae.  Species in the genus are known generally as trumpets, mountain trumpets, or trumpet flowers.  They are native to North America and southern South America.  The genus name comes from the Greek "kolla" ("glue"), a reference to the seeds, which become gelatinous in texture when wet. Olearia is a genus of flowering plants belonging to the family Asteraceae.  There are about 130 different species within the genus found mostly in Australia, New Guinea and New Zealand.  The genus includes herbaceous plants, shrubs and small trees.  The latter are unusual among the Asteraceae and are called "tree daisies" in New Zealand.  All bear the familiar daisy-like composite flowerheads. 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". A mandrake is the root of a plant, historically derived either from plants of the genus "Mandragora" found in the Mediterranean region, or from other species, such as "Bryonia alba", the English mandrake, which have similar properties.  The plants from which the root is obtained are also called "mandrakes".  Mediterranean mandrakes are perennial herbaceous plants with ovate leaves arranged in a rosette, a thick upright root, often branched, and bell-shaped flowers followed by yellow or orange berries.  They have been placed in different species by different authors.  They are very variable perennial herbaceous plants with long thick roots (often branched) and almost no stem.  The leaves are borne in a basal rosette, and are very variable in size and shape, with a maximum length of 45 cm .  They are usually either elliptical in shape or wider towards the end (obovate), with varying degrees of hairiness.
Answer: Calendula