Photoperiod evidence in the introduction of xanthium (cocklebur) to australia.

North American populations of cocklebur Xanthium strumarium L. are diverse in form and show critical dark periods ranging from 7.75 to 10.

Photoperiod in three xanthium populations from the tropic of cancer in Mexico.

Diverse photoperiodic responses were shown by three populations of Xanthium strumarium L. originating between 22 degrees and 25 degrees N on the western coast near Culiacán, Sinaloa; in the Chihuahuan Desert near Matehuala, San Luis Potoś; and on the Gulf Coast near Ciudad Mante, Tamaulipas, respectively. A combination of differences in critical night length and in ripeness-to-flower response (maturity) appears to be the basis for reproductive adaptation of these populations to different climatic regimes that prevail at the same latitude (and photoperiodic regime).

Phenological Variation within Seven Transplanted Grassland Community Fractions from Texas and New Mexico.

Community fractions, consisting of population samples of Andropogon scoparius Michx., A. gerardii Vitman, Panicum virgatum L.