Seed biology of rush skeletonweed in segebrush steppe

Rush skeletonweed (Chondrilla juncea L.) is an invasive, herbaceous, long-l ived perennial species of Eurasian or Mediterranean origin now occurring in many locations throughout the world. In the United States, it occupies ove r 2.5 million ha of rangeland in the Pacific Northwest and California. Desp ite the ecological and economic significance of this species, little is kno wn of the ecology and life history characteristics of North American popula tions. The purpose of this study was to examine seed germination characteri stics of 2 populations of rush skeletonweed in Idaho. Seeds from rush skele tonweed plants in southwestern Idaho were collected during the 1994 and 199 5 growing seasons. Mature seeds were harvested on 6 dates between early Jul y and early October 1994, and on 5 dates between early July and late Septem ber 1995. Fresh seeds from each harvest period were measured to determine s eed weight, total germination, rate of germination, and viability (tetrazol ium staining [TZ]) of non-germinating seeds. An aliquot of seeds collected in 1994 was also stored for 1 year to examine the effects of seed storage o n germination. In southwestern Idaho, rush skeletonweed produces seeds cont inuously from mid-July through October. Seeds were capable of immediate ger mination without scarification or wet prechilling. Total germination genera lly ranged from 60 to 100% throughout the entire seed production period. Ge rmination was also rapid, reaching 50% of total germination in less than 12 days. In general, germination was higher at the lower incubation temperatu re regime (20/10 degreesC), perhaps reflecting origins of this species in M editerranean winter rainfall regions. The TZ testing indicated that 30 to 6 0% of non-germinating seeds were viable, suggesting that seeds may persist in the soil seed bank. Up to 60% of seeds remained viable following 1 year of storage. Stored seeds generally exhibited higher germination rates ((x) over bar = 90%) than fresh seeds ((x) over bar = 67%), indicating possible dormancy and afterripening effects. Germination characteristics of this spe cies are consistent with those of other invasive alien species, and favor r apid population growth leading to community dominance.