Helianthus annuus and H. argophyllus are the most common species of sunflowers in Nueces County, Texas.  In previous work we found that H. argophyllus is restricted to sandy sites, while H. annuus is nearly restricted to clay sites. To determine if the germination phase of development plays a role in this distribution, we investigated germination of locally collected seed of H. annuus and H. argophyllus on sand and clay soils.  We germinated four trays of 128 seeds of each species on each soil type under lights in a growth room.  Number of germinants in each tray was our measure of germination.

Results/Conclusions

An analysis of variance indicates that germination does not differ significantly between species (P = 0.58) or with soil type (P = 0.12).  In addition, no interaction between species and soil type (P = 0.84) exists.  We conclude that the germination phase is not involved in restricting these species to soil types on the Texas Gulf Coast.  Future research will focus on other parts of the life cycle and other possible mechanisms, such as competitive interactions and water relations, to explain the distribution of these species.