The Zygophyllaceae, or Caltrop Family is a small sized family of flowering plants. World-wide The Plant List includes 26 genera with 211 accepted species names. The largest genera globally are the type genus Zygophyllum with 69 species, followed by Kallstroemia with 31 species. In North America, the family has only 9 genera and 20 accepted taxa overall. The largest North American species is Kallstroemia with 7 species.
The Caltrop family consists of herbs, shrubs and small trees in tropical and warm climates, arid, sometimes saline soil habitats.
Caltrop plants of note: A well-known member of this family is the Creosote Bush, Larrea tridentata, of the southwestern United States. Another family member is the notorious noxious European weed, now naturalized in North America, called Goat-heads or Puncture Vine, Tribulus terrestris. Aptly called Puncture Vine and you would not readily forget the excruciating pain in your foot if you ever stepped on one of these sprawling plants. I recall in years past the plants were so numerous as to regularly flatten bicycle tires.
Common characteristics: of native southwestern United States species. Plants: herbaceous or shrubby, stems with multiple branches, stems often angled and swollen nodes; Leaves: stipules persistent or deciduous; leaves compound or pinnately dissected, alternate or opposite; leaflets margins entire; Inflorescence: flowers in 1-2 axils; Flowers: perfect, regularly or nearly so, solitary, 4- to 6-merous, stamens more numerous than the petals in 2 whorls, style 1 or styles united, sepals 5, free, persistent or deciduous, petals 5, free, sometimes twisted and propeller-like, petals yellow, orange, purple; Fruit: a capsule or splitting into 5 or more nutlets.
Native species in the southwestern United States are Fagonia, Guaiacum, Kallstroemia, Larrea and Tribulus.