SHOOT ARCHITECTURE AND EVOLUTION OF DICENTRA-CUCULLARIA (PAPAVERACEAE, FUMARIOIDEAE)

Species of Dicentra have diverse shoot systems, including a group with subterranean shoots that share the evolution of tuberous diaspores. W e characterize the shoot architecture of D. cucullaria and compare it with related members of the genus. Ramets of D. cucullaria are sympodi al and, at the time when foliage leaves are aboveground, generally con sist of three orthotropic modules. The youngest of these three modules is the renewal module, the next oldest bears current foliage leaves a nd flowers, and the oldest flowered and had foliage leaves during the previous growing season. Renewal buds form 2 yr before their foliage l eaves and flowers extend aboveground. Each orthotropic module bears di morphic tuberous diaspores. We demonstrate that the tuberous diaspores of D. cucullaria are specialized leaf bases. Large tuberous bases are characteristic of foliage leaves and other nonfoliage leaves position ed on the axis distal to the foliage leaves. Smaller tuberous leaves w ith rudimentary, apiculate laminas are positioned on short branches th at form in the axils of scale leaves subjacent to the portion of the m odule axis where the foliage leaves are located. Both forms of tuberou s leaf bases bear multiple, epiphyllous buds. Although both forms of t uberous leaf bases may function in asexual reproduction if detached, o nly the small tuberous leaf bases borne on the short branches separate easily from the ramet. Some of the short branches that bear small tub erous leaves elongate distal to these leaf positions to form plagiotro pic rhizomes that produce new ramets. The shoot architecture of D. cuc ullaria is very similar to that of its hypothesized sister taxon, D. c anadensis. These two species appear to form a monophyletic group with D. pauciflora and D. uniflora based on their shared derivation of tube rous leaf bases. The relationship of this monophyletic group to other species of Dicentra is unclear.