SHADE TOLERANCE AND ITS EFFECT ON THE SEGREGATION OF TWO SPECIES OF LOUISIANA IRIS AND THEIR HYBRIDS

Abstract

Iris fulva Ker. Gawler and Iris hexagona Walter have overlapping geographic ranges in Louisiana. In areas of overlap hybrids are fairly common. Iris hexagona occupies the borders of freshwater marshes of southern Louisiana while I. fulva can be found farther north along edges of natural levees, canals and swamps. Where the natural levee penetrates the marsh, natural hybridization can occur between I. hexagona and I. fulva. It has been suggested that one principal explanation for the segregation of the two species is that I. fulva grows best in semishade and I. hexagona grows best in full sun. A greenhouse study was conducted using rhizomes collected from the field to test this hypothesis and determine the relative shade tolerance of two natural hybrid types. Iris fulva, I. hexagona , and the two hybrid taxa were grown under 0% (control), 50% (medium shade), and 80% (high shade) reduction of sunlight for 6 months and then harvested. Iris fulva was found to be more tolerant of shading than I. hexagona and the two hybrids. Further, I. fulva was found to grow as well in control as in medium shade. Both hybrid taxa were more shade tolerant than I. hexagona. Iris hexagona was greatly affected by all levels of shade. In general, the results suggest that these hybrids are intermediate to the parental taxa in terms of shade tolerance.