A rhizomatous, perennial form of Microstegium vimineum (Trin.) A-Camus in New Jersey

Populations of Microstegium vimineum (Trin.) A. Camus have been found in New Jersey containing individuals that have clusters of large rhizomes, and which evidently exhibit the perennial growth habit. This species, a major invasive exotic pest throughout the east coast,has previously only been known as an annual, both in the US and in its native geographical range in temperate and tropical Asia and India. Rhizomatous plants were observed in 6 populations, in sites ranging over a 100 km distance, and accounted for 8-15% of the culms in each population. Lower nodes of decumbent culms have on average 4 rhizomes (maximum 13 per node and 23 per culm were observed), which are 0.1 to 7 cm long (mean 1 cm). Significant differences in the number of rhizomes per culm and the size distribution of rhizomes were found among three sampled populations. Rhizomatous specimens had open, exserted terminal panicles which flowered 2-3 weeks before the non-rhizomatous specimens, which have cleistogamous spikelets within the leaf sheaths and a variably exserted, closed terminal panicle. Rhizomes sprouted in the greenhouse, after cold treatment, demonstrating their perennial capacity. This is the first reported occurrence of rhizomes in the genus, and also is the first apparent example of a trade-off between annual/perennial life history and cleistogamous/chasmogamous reproduction. In addition to the implications for the evolution of plant life history characteristics and breeding systems,the finding has important implications for control strategies for this invasive plant species; current recommendations for its control will not be effective against perennial forms.