A study of the vascular flora of the Middlesex Fells Reservation, a suburban forest reserve in greater Boston, was made over nine years from 2003 to 2011. We compiled a checklist, determining the frequency of each taxon and documenting all natural community types occurring in the reservation. We compared our findings to those made in the 1890s, and attempted to explain changes in species composition and frequency. Despite many impacts on the reservation in the last century, a high level of species richness was observed, with 868 vascular taxa extant, including 563 native taxa. There was little net change in the number of native taxa found, but a near tripling of non-native taxa from 110 to 305. Habitat destruction, fragmentation, forest succession, fire suppression, trends favoring mesophytic vegetation, climate change, and invasive species are all believed to be factors in the changes observed in the flora.

Juncus brachyphyllus is a plant of floodplains, prairie remnants, and glades in the Midwest, from Tennessee to Texas, north to Illinois and Nebraska. Disjunct plants called J. brachyphyllus from Idaho to California are described here as a new species, J. trilocularis. They are distinguished by smoother stems and longer styles, and frequently have longer anthers. Rare putative hybrids between J. confusus and J. trilocularis are discussed from Lassen County, California and Kittitas County, Washington. Another putative hybrid, between J. occidentalis and J. trilocularis, is reported from Butte County, California. The new species is assigned to Juncus section Steirochloa Griseb., and a sectional key is provided for western North America.