Unknown Plant

Unknown herbaceous perennial growing outdoors at Bellevue Botanical Gardens in Bellevue, Washington. Leaves are about 6 in / 15 cm long, stems are about 18 in / 45 cm to 36 in / 90 cm high. Growing in moist shade. Plant seems to spread slowly via underground stems. Stems are mildly jointed and somewhat brittle. Any ideas what this might be?

Done