''Isocarpha oppositifolia'', the Rio Grande pearlhead, is a New World species of plants in the family

Asteraceae The family Asteraceae, alternatively Compositae, consists of over 32,000 known species of flowering plants in over 1,900 genera within the order Asterales. Commonly referred to as the aster, daisy, composite, or sunflower family, Compositae ...

. It is widely distributed in eastern and southern Mexico, Central America, the West Indies (Cuba, Jamaica, Bahamas, Caymans, Trinidad), and northern South America (Colombia, Venezuela). The range extends northward, just barely crossing to the north side of the

Río Grande The Rio Grande ( and ), known in Mexico as the Río Bravo del Norte or simply the Río Bravo, is one of the principal rivers (along with the Colorado River) in the southwestern United States and in northern Mexico. The length of the Rio G ...

in the two southernmost counties in

Texas Texas (, ; Spanish language, Spanish: ''Texas'', ''Tejas'') is a state in the South Central United States, South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2 ...

(

Cameron Cameron may refer to: People * Clan Cameron, a Scottish clan * Cameron (given name), a given name (including a list of people with the name) * Cameron (surname), a surname (including a list of people with the name) ;Mononym * Cam'ron (born 1 ...

Hidalgo Hidalgo may refer to: People * Hidalgo (nobility), members of the Spanish nobility * Hidalgo (surname) Places Mexico * Hidalgo (state), in central Mexico * Hidalgo, Coahuila, a town in the north Mexican state of Coahuila * Hidalgo, Nuevo Le� ...

).Biota of North America Program 2014 county distribution map
/ref>David J. Keil & Tod F. Stuessy. 1981. Systematics of ''Isocarpha'' (Compositae: Eupatorieae). Systematic Botany (1981) 6(3): pp. 258-287
descriptions, line drawings, distribution maps for all 5 species ''Isocarpha oppositifolia'' is an herb or subshrub up to tall. Leaves are up to long, usually narrow but sometimes egg-shaped. One plant produces several flower heads, each a long flower stalk, each head with 60-150 disc flowers but no ray flowers.

References

External links

in Spanish with photos
Photo of herbarium specimen at Missouri Botanical Garden, collected in Guatemala in 2008
Eupatorieae Flora of Northern America Flora of Southern America Flora of Central America Plants described in 1759 Flora of the Caribbean Flora without expected TNC conservation status {{Eupatorieae-stub