Guilleminea is a small genus of plants in the family Amaranthaceae. They are sometimes known as matweeds. These are prostrate, mat-forming perennial herbs growing from taproots. The genus includes seven species native to the Americas, ranging from Arkansas, Colorado, and California to northern Argentina.^[1] The best known species is perhaps Guilleminea densa, the small matweed, which has been introduced to parts of Africa, Australia, and the eastern United States where it is a weed.

The genus was named after the French botanist Jean Baptiste Antoine Guillemin.

The genus contains seven species.^[1]

• Guilleminea chacoensis Pedersen – Paraguay and northeastern Argentina
• Guilleminea densa (Willd. ex Schult.) Moq. – Oklahoma, Colorado, and California to northern Argentina
• Guilleminea elongata Mears – Uruguay
• Guilleminea fragilis Pedersen – Brazil (Mato Grosso do Sul) and Paraguay
• Guilleminea gracilis R.E.Fr. – Colombia, Ecuador, Peru, Bolivia, and northwestern Argentina
• Guilleminea hirsuta Pedersen – Bolivia to northwestern Argentina (Salta Province)
• Guilleminea lanuginosa (Poir.) Benth. & Hook.f – Arkansas to New Mexico and northern Mexico, Hispaniola

• Jepson Manual Treatment
• USDA Plants Profile: North American Species