Species: Hemizonia pungens

We found no literature on the ecology of Hemizonia pungens but some work has been done on other members of the genus. One study by Morse (1988) found that seed set in another summer-flowering species, H. luzulifolia DC ssp rudis, was insensitive to both atmospheric and soil drought. The plants coped with the drought by continual root growth into deep soil-water reserves and by storing water in extracellular polysaccharides. The polysaccharides apparently help maintain tissue water balance and buffer cells from rapid changes by releasing water as plant water status declines. Morse (1988) also found that tissue water storage (capacitance) of above-ground shoots increased from low values in the relatively wet spring to very high values in the hot, dry summer. Greenhouse studies indicated that the increase was genetically determined, not environmentally induced. During drought periods, plants that received moisture as dew were able to continue photosynthesizing longer and to keep their flowerheads open for pollinator visitation longer. The latter factor was important because Morse (1988) found that seed set could be limited by reductions in pollinator visitation resulting from early flowerhead closure. However, the primary factor responsible for limiting seed production was the destruction of flowerheads and seeds by herbivores. <br><br>We were not able to obtain information on the insects that feed on Hemizonia pungens. English-Leob (personal communication) made observations of the closely related species H. luzulaefolia in California's Central Valley and found that it was fed on by larvae of the noctuid moths Heliothodes diminutivus and Heliothis phloxiphaga, and the plume moth Trichoptilus californicus, a tree cricket (Gryllidae) in the genus Oencanthus, flea beetles (Chrysomelidae) and the spittle bugs Philaenus spumarius. Impacts: (THREATS POSED BY THIS SPECIES) Hemizonia pungens was introduced to the Columbia River basin of northeastern Oregon and southeastern Washington within the last century where it behaves as an invasive weed. In 1988 it was discovered on the 386 acre Lindsay Prairie Preserve in Oregon's Columbia River Basin. At that time it dominated a total of 4 acres but the infestation spread rapidly. By 1992, fifteen acres of the preserve were infested and spikeweed densities averaged 750 individuals m-2. Morrow County, where the preserve is located, has placed spikeweed on its Noxious Weed List as has neighboring Umatilla County and several counties across the river in Washington. In November 1992, Morrow county served the Oregon Field Office legal warning that it must control the infestation on Lindsay Prairie. <br><br>The species poses no known threats within its native range.