[wikipedia] Description, Varieties: Juncus phaeocephalus is a grasslike perennial with stout, creeping rhizomes. It has flattened stems that are two-edged and can grow up to 1.5 feet (0.46 m) tall. Its leaves are shorter than its flowering stems. Flowers have a brownish color and appear in spherical clusters at the tops of the flowering stems. Brown-head Rush may be mistaken for sedges or irises because of its stems and leaves.[5] This plant produces many seeds. These ovoid seeds are about 0.6 mm in size.[6] Varieties Juncus phaeocephalus is a variable species in which several subspecific varieties have been characterized mainly on its branching patterns of the inflorescences. Named varieties include:[7] J. phaeocephalus var. phaeocephalus, plants with few, many-flowered heads. J. phaeocephalus var. paniculatus, plants with many, few-flowered heads. J. phaeocephalus var. glomeratus, plants with many, many-flowered heads. (link added by Mary Ann Machi)

[wikipedia] Poisonous Plant: Poisonous plant According to the tests made on the plants at the Chemistry Laboratory of the California Department of Food and Agriculture, Juncus phaeocephalus has as much as 30 ppm of hydrocyanic acid present in the plants. Due to its volatile nature, the concentration of this chemical might have been greater before the actual testing was made. One actual case of hydrocyanic acid poisoning from a common rush occurred in California. In December 1958, two dairy heifers were found dead on a farm land near Petaluma, Sonoma County. The heifers died due to consumption of Juncus phaeocephalus plants.[8] Juncus phaeocephalus grows in plant communities with Verbena spp., Mimulus guttatus, Eleocharis macrostachya and Agrostis densiflora.[9] (link added by Mary Ann Machi)